Lathe - Thread Cutting - General



Threading part I-II-III (Jul 13, 2001) Threading Questions (Feb 10, 2004)
Threading (Jul 16, 2001) Correct Thread Depths without Calculation (Feb 12, 2004)
Need a few tips (Feb 19, 2002) More Threading - Tapered Pipe Threads (Feb 15, 2004)
Thread Cutting problem on a 9A (May 20, 2002) Threading Primer anyone? (Mar 8, 2004)
Threads Feeds (Sep 28, 2002) Threading question (Apr 2, 2004)
Threading (Nov 3, 2002) First Threads (Apr 27, 2004)
Screw Thread Transposing Charts (Dec 15, 2002) Threads on a long rod (14 feet)? (Oct 25, 2004)
Threading? (Feb 9, 2003) Threading your bar stock (Oct 26, 2004)
Screw cutting at 25 degrees (Feb 13, 2003) Newbie trying to thread on a heavy 10 (Nov 17, 2004)
Threading question (Mar 28, 2003) 480 TPI (Dec 6, 2004)
Threading on 9 A (Apr 24, 2003) Threading with tailstock die holder (Dec 11, 2004)
Now that's what I call a fine thread (May 7, 2003) Cutting 27 tpi? (Dec 17, 2004)
Thread size (May 22, 2003) Thread pick-up troubles (Jan 19, 2005)
Threading question (Oct 3, 2003) Internal Threading Bars (Jan 24, 2005)
Cutting threads without a thread dial (Oct 20, 2003) 1 1/2-8 Threads (Feb 28, 2005)
Rough External Threads (Dec 23, 2003) Screwcutting with compound set parallel to bed (Mar 9, 2005)
Threading drill rod? (Dec 27, 2003) Looking for a source for a threading tool (Mar 18, 2005)
Can you cut finer than 160 TPI on a 9" C? (Jan 25, 2004)  
Threading part I-II-III
HOW TO CHASE THREADS ON ANY LATHE 1.SET-UP- Use a fishtail to grind your 60 degree tool bit. A slight top grind so the tip is higher then the back. Chuck the piece up and use a center to support the end in the tail stock. Next, position the compound in line with the cross-feed so the handles line up. Now, kick the compound over so your tool moves TO THE LEFT. Look at the degree markings on the side. You want 29 1/2 degrees from your starting point. I say it this way because each brand of lathe can be marked out differently. Tighten the 2 set-screws holding the compound in place. With the bit in its holder, square it to the work-piece using your fishtail threading gauge. It is very important that the ground POINT be square to the work. And just slightly below center. Do this by taking your 6" scale and place it gently between the work and the work-piece using slight pressure. This .025 thick scale will tilt towards the work if the tool is high; and tilt towards the operator if it is below the centerline. It is a very accurate way of setting any tool-bit in any lathe. Once you've got that squared away select your feed and speeds. Use a slow spindle speed. Double-check your work. Lets talk a moment about the chasing dial. Lathes differ in how the dial is set up. Many of the machines I have run will read: even threads any line, odd threads any number, multi lead threads...that is a whole 'nother world. Now you can be pretty safe in threading by going back to the SAME spot each time. In fact you can thread without a dial, just leave the half-nuts engaged. At the end of each cut, crank the tool out of the cut and reverse the lathe. Now it is a good idea to practice your indexing. Each lathe has a different 'feel'. The 'sweet-spot' for each dial must be found. ANTICIPATE the index. You will understand this when you work with it. Even the most worn-out dials can still do good work. OK it is time to set your dials. Start with the compound. Run the compound out, then run it back in until your tool-post is roughly centered over the center of the cross-feed. Set your dial to '0'.Now bring the cross-feed in until it barely touches the work. Set this at '0'. This will be your home-base. In fact, wipe the cross-feed casting and pencil a mark on it to come back to. END OF PART I Ron (1079)
THREADING ON A LATHE PART II RUNNING THE JOB - Your tool is set, gearing is set, spindle-speed set, appropriate sacrifice to the local gods done. Now it's time to run this turkey. Turn on the machine and take .005 on the tool-bit. You can engage the dial by moving the carriage until the nuts engage THEN turning the lathe on. At this point you are committed. DO NOT DISENGAGE THE GEAR-TRAIN FOR ANY REASON! That is, the head-stock and the thread gears should never be disengaged from one another. If you want to see the first pass clearly, paint on some layout-fluid on the work first. At the end of the cut pull the tool out at the same time you open the half-nuts. This can take a bit of time to learn, so practice this BEFORE DOING THE ACTUAL WORK. Almost any single-point thread has an 'escape ditch' at the end of each cut. Go back to your cross-feed 0 and take another .005 on the tool. Use some oil. Either black sulphur thread-cutting oil or 90Wt gear or Hyploid oil. As you progress into the cut, take spring cuts for every 2 in-feed cuts. This means go back over the work without advancing the tool. This will save you the embarrassment of having the tool dive into the work ruining it. When it looks like your getting near the finish-size, you may want to try the nut on the shaft your threading. When the last few passes are in sight advance the tool in using the CROSS-FEED DIAL ITSELF. Being sure to note where it comes back to. This will clear up both sides of the thread. IN GENERAL, that's about it. In a third article, I will cover some finer points. Like what do I do when the whole thing screws up, I broke the damn tool, and re-setting the tool in the thread. Ron (1080)
Before I get into today's subject I'd like to address tool forming for a minute. In most manuals much is said about the angle of the tool bit faces in relation to one another. In my years of being a machinist doing both proto-type and production work, I have used a very simple set-up for all my tool-bits. All I did was enlarge the tool-rest on my grinder and set it at a 4 degree angle. With the possible exception of a parting tool or square-thread, I leave it there. By replacing the stage that came with the bench grinder with a 3" piece of 2X2 angle iron, you increase the ease of tool sharpening. Tool rests on most grinders are only good for ruining your tool, your fingers, and your day! Slot the new stage and make a handle for it that doesn't require you to dive for that adjustable you keep in your hip pocket. I always start with the top. Four degrees is plenty of cutting angle. You only want to grind enough to get a clear dished land. Tip the tool so that the tip is the highest point of your bit. Next form the front. If your going to use it for turning a shaft TOWARDS the chuck, angle it slightly in that direction. When you get a full face STOP. Now for left-side clearance. The stage is still set for that 4 degrees. Lay the left side of the tool,(the leading edge) against the wheel. Just use firm pressure dipping it in water to keep your digits cool. When it has a clean face stop. Now, take a small stone, India stones are nice, diamond is better but expensive. Hold the stone by the ends in one hand and the tool bit in the other. Carefully stone a small radii at the point. I use a back and forth movement while slowly turning the tool.This actually gives your tool a longer life. NEVER leave a sharp point on a tool when working metal. It is the first thing to break. One reason I like this set-up is that I can rotate my tool against the wheel forming a small radii. Then I go back and hand stone it. This is very handy when your doing radius work for a shoulder. WOW! Didn't think I'd get this far a-field! I tend to 'run my gator' when I get on a favorite subject. But, this is a VERY short course in cutter-grinding. Now let's get back to work. INTERMISSION, TAKE A LEAK, PAT THE WIFE AND GET SOME COFFEE INTERNAL THREADING PART I 1.Start with your tool-bit. It is nothing more then a boring-bar that has a threading tip. V-threading is always done with a 60 degree point. The leading edge of most threading tools tilt away from the work as a compound angle. This double angle is what does the cutting. 2. Once your tool is ground tilt the compound 29 1/2 degrees to the RIGHT. I other words, in the opposite direction as your external threading operation. When you begin to cut the thread, you will be cranking the compound OUT instead of IN. Always feed the compound in the direction of the thread. When we get into left-hand threading, you will see this is still true. 3. As before, set your bit with a fishtail so that the V-form of the tool is 90 degrees to the work. If you grind your tool using a small protractor set to 30 degrees, it will help to keep your tool form square to the shank. This will help later when you are setting up the job. 4. Once this is all done ditch the job. Use a scale and find the back end of the cut. Mark the point on the bed with a magic marker. Now turn on the machine and use your cutting tool to under-cut the end of the thread. This is your 'foxhole'. Because it is near impossible to stop the cut and back out the tool all at once before you crash into the wall, you ditch it. About 3 threads long should do it. 5. Now for an indicator of some kind. Start by laying a very visible mark on the threading tool. Next you need to set up something a bit more reliable on the bed. A lathe-stop may only be trouble. A 1" travel indicator is ideal. Cheap ones for under $20 work well. If I had the extra shekels I'd go for a 2". These things are invaluable for lathe work. With them you can do VERY accurate shoulder and groove work. Barring that grab a magnet and a white strip of paper. Clean off the excess oil with a rag and place the magnet on the strip of paper where your ditch is. Why do this? It is a highly visible line to stop at that should you miss your ditch, won't do damage to the lathe...just your tool. As in your external threading it's a good idea to practice your moves BEFORE you do the cut. I do. As you come to the end of the cut, you only want to release the half-nuts, nothing more. Until you get the hang of it, this will be a bit nerve-wrecking. But, like a stone, it will pass. 6.Time for pucker-power. The gears are set, you have put a mark on the cross-slide as a rough 0 mark. Your dials have all been zeroed as before. Lay on some oil and courage and get cutting. Remember, since your cutting with a bar instead of a bit take no more then .005 at a time. Until you get good at it, do a spring-cut every other cut. Use back-gear. Remember you will be feeding the tool in by turning it to the LEFT on your compound. If you are using a dial, set it at .01 NOT 0! You want to see it coming so you can anticipate the end of cut. When you arrive in your ditch, the cross-feed should be dialed IN NOT OUT! 7. It is always a good idea to start the run by champhering the end of the piece with your tool. It looks professional and makes starting your male thread easier. Use oil, it's cheap. When your close to finishing, use the cross-feed to clean up both sides of the thread. IN GENERAL- Most guys I know tend to groan when they hear the subject of single-pointing internal threads. It is not all that bad. Doing things like using the largest diameter boring-bar you can stuff in the hole and sharp tools makes it much easier. A 1" hole should be threaded with a 5/8" bar. Just remember, you can use as big a bar as the total width of bar, cutter AND lee-way for getting out the ditch as you want. I don't like using thin flimsy boring-bars. They are nothing but trouble. One final point. Single-pointing internal threads will create a small amount of 'bell-mouthing'. This is a condition that results from the tool going back over the end of the work repeatedly. There is not much you can do about it. Ron (1101)
Great post Ron. Might I make a suggestion for internal threads? For years now, I have ground my tool bits backwards, so they cut on the back side, and run the machine in reverse. This lets you cut from your "ditch" to the open end. Solves two problems. No more bell mouthing as the tool starts to cut under load. And the big plus, you aren't courting disaster by cutting toward a blind shoulder. I haven't crashed a high dollar threading tool in 15 years! (1102)
Although I have not done internal threading this way, I found that my model C did not give me good results when cutting away from the spindle on a left hand thread. I wound up turning the tool upside down and running the spindle backwards. Since that worked out well I did not investigate this problem but obviously lash in the machine was causing the tool not to track consistently in this direction. Threading away from the spindle has definite advantages, but this may be a problem to look out for if you try it. Tom (1104)
Skip has touched on an idea I read about in a book written by an engineer that worked on the SR-71 program. In that chapter he recommends turning the parting-tool upside-down in order to avoid hogging in and breaking the tool. As a matter of fact he also urged the reader to run all work clock-wise using the tools upside-down. This has the advantage of better finishes and no hogging. Since the tool tends to spring in the opposite direction of force, it is pushed away from the stock. I always use this method when parting-off. It works very well on small lathes. HOWEVER, (there always seems to be one of those around!) many of the bench or precision lathes have RIGHT-HAND THREADS. It is possible to have your chucked-up work visit the Space Shuttle! The problem of course can be fixed by figuring a way to pin the chuck to the spindle. Just HOW to do this without ruining the threads I'm still thinking about. In the mean-time cutting left-hand threads are done using the same basic procedures as discussed in the first unit on threading. The exception being that you cut these threads by reversing the lead screw so that it rotates opposite to the work, with the cutting tool moving from left to right. As before in internal threading, a ditch for starting is necessary. One of the guys asked me about cutting a left-hand worm for another lathe. Ron (1105)
Tom and Ron have both touched on problems with my method of internal threading. I admit to never cutting an internal thread on my model C. I suspect the trouble Tom had was excessive end play in the spindle. The model C doesn't have a very stout thrust washer at the rear. It is, however, very easy to adjust. You should keep spindle play at an absolute minimum even when doing normal turning. Excessive play will result in rough finishes. I would NEVER try to cut off on a machine with a threaded spindle with the machine in reverse, even if you had fitted the chuck with a set screw. Doing so WILL eventually result in damage to things you never knew were damageable! Threading however, exerts far less cutting force and should be safe if you install your chuck tightly. The only time I had my chuck unscrew was with a heavy work piece mounted and the machine reversed before the spindle stopped. The damage was incredible and instantaneous! (1106)
Skip, You got me curious about that spindle end play so I checked it tonight-it's about .0015, almost too tight. I suspect the play is in the halfnut (had it apart, doesn't look the best) as I never have had problems with other operations. As far as running cutoff tools upside down, it's been done that way on turret lathes and screw machines almost forever and does have its advantages. I ran across somebody on the web who offers a T-slotted cross slide that allows for a rear tool post as in turret lathe practice. This has the advantages of mounting the tool upside down while running the spindle forward. Tom (1108)
The slotted cross slide is offered by Andy Lofquist at Metal Lathe Accessories http://www.sc-c.com/metallathe/ (1109)
Tom, my referral to not using a tool upside down was meant to say "don't run a threaded spindle machine in reverse when taking a heavy cut". Sorry if I confused you. (1112)
No confusion, Skip. I was referring to Ron's post wherein he made mention of the advantages of running cutoff tools upside down. The rear tool post just provides a safe way to do that on the South Bend. Tom (1126)
Need a few tips
I've been trying to turn a single point thread on my 10K and the pitch I need is 14 TPI. Now, I made sure I was on the "20" gear and set the left tumbler to the "A" position. The right tumbler all the way to the right (on the chart these settings line up with "14 TPI"). The thread that is cut is way too fine though, How can I be sure I have the right gear in place on the adjustable carrier? I only got the one on the lathe so I assumed it was original but this dilemma has me wondering. (3314)
The setup sounds correct. How fine is fine? You gotta make sure you're using the half-nuts not the clutch for the power long feed. Also, (at least on a 9") the 20 tooth gear goes on the outermost of the reverse tumbler. The 40 tooth should be stored on the QC gearbox input shaft above the 56(?) tooth gear. Attached is a picture of the gear train from my 9" model A. Any of that help? Paul R. (3315)
Paul, First off I was using the clutch (duh!). I fixed that and tried again. I posted the photos in the photo section under "single point problem". Now I'm getting 10 TPI when it's setup for 14. I'm closer, but no cigar, and I really like cigars! :-) Bill (3318)
Good pictures. Here's the deal. You've got the two gears on the QC input reversed. The outer gear (just riding along) should be the 40T, and the one that's engaged with the 80T idler should be the 56(?) tooth gear. Swap 'em. (40/56) * 14 = 10. Paul R. (3320)
Paul, I swapped that gear around and everything worked out great! I posted a pic it that same directory of the successful cut. Bill (3323)
Great, Bill, and I will never divulge how I knew about the power-long feed vs. the half nuts. Paul R. (3325)
Thread Cutting problem on a 9A
After making the first cut and checking it for accuracy I continue with successive passes using the thread dial for the proper starting point. For no apparent reason the tool will advance a half thread and start at the wrong point. I have checked the thread dial adjustment and everything is fine there. If you watch it you can see the saddle jump ahead when you close the half-nut at the point it goes bad and fowls up the thread. Clio (4261)
The thread dial has some backlash, as do the threading gears. And the leadscrew probably has some end play. This all means that the thread dial reading will only be meaningful when the leadscrew is engaged and has driven the carriage (in the correct direction) for a substantial fraction of a screw turn - which may be several spindle rotations depending on the thread pitch. Or did I miss understand - did you mean it jumps at a certain position on the leadscrew every time? That would suggest a damaged screw and probably nuts too. Chris (4262)
Basically you have it right. The leadscrew is turning and the threading dial is turning. When the mark comes up and I close the half-nut some times the carriage will jump ahead slightly and that is when the tool has advanced a 1/2 thread and ruined the work. GDS (4264)
Jerry, I think Chris is right. It sounds like the lead screw is moving back and forth in the gear box. When I did my C to A conversion, I had to use my old lead screw. The one I got with the gear box was for a shorter lathe. To fit the lead screw to the "new" gear box I trial fitted it and then cut down the flat where the gear seats until the lead screw had very little end play. You can do the same on your lathe. Just check how far the lead screw moves when you shove back and forth on the cross slide and add spacers or face off the gear seat to match. Glen (4265)
Jerry, Your description sounds as though you will find a problem somewhere in the feed system. As a starting point, I would check everything in the gear-train starting at the spindle and working my way to the QC box, then through the lead screw and the apron. Look for loose nuts and gears, sheared keys, etc. (Have you changed any gears lately?). I once had a job where one piece was required and it took 3 attempts because of an un-detected slip of one gear on its shaft. Raymond (4266)
Jerry, I purchased an old 13" SB with QCGB (c. 1922) which was not wired so I could not check for screw-cutting, power-feed, etc. When I finally got a motor and got it wired up and then tried to use the power-feed on a scrap piece of metal, I found that the carriage would move along normal for about 1/4 revolution and then, when it should have been cutting metal, it would rotate 'wildly' with no advance in lead-screw positioning. My friend Al, an excellent tool and die maker, helped me investigate and fix our problem. The clutch knob shaft (star-wheel shaped) was broken at the back end. It was prevented from falling off but, when pressure (in this case the engagement of the Automatic Feed Friction Clutch) was applied, the shaft would rotate but because it was broken, no advancement in feed was obtained. Although not exactly your problem, you might want to inspect for broken shafts, etc. BTW, Al made a new shaft out of a tough metal and there have been no further problems in this regard. Barry (4273)
Threads Feeds
Do some Southbend lathes list feed rates in TPI? I ask a seller what the feed rates of his lathe were and he tells me 4-224 TPI . I say that is the threads and he says yes threads and feeds. Did SouthBend ever make such a machine? It's a 13" machine made in 1959. What would typical feed rates be on a SouthBend of that size and age. Sangtipcoke (6481)
They are both listed in the same matrix bounded by the two gear levers and there various positions. There are two numbers in each matrix position. One for threading (TPI) and one for feed rate. Two levers on the apron are mutually exclusive, one for threading and one for feeding, longitudinally or crossfeed if the model supports crossfeed. The seller is correct in the thread range he quotes. As for feed rates they range fast to slow in direct correlation with the coarseness of the threads. Ask him to tell you the range of the floating point numbers. TPI are represented as integers and a couple like 7 1/2. On the 9" the range from 4 up to I think 7 1/2 require a different feed screw gear. From 8 on up the same gear is used. Jim (6483)
Hi Alan; On my top lever gearbox, there is a legend that fine feed is 4 times the tpi. The range on my old lathe is 2 to 112 TPI, for a finest feed of about 2.2 thou per revolution. Assuming 224 TPI on your gearbox, this works out to a finest feed of 0.001116 per revolution, or about 1.1 thou advance per spindle revolution. While my lathe is a '29 SB13, I think the ratio remains true when they went to double tumbler gearboxes, as the apron remained quite similar. Threading is done via direct engagement of the halfnuts, while fine feed is via a worm and wheel driving a gear train in the apron, giving the 1:4 reduction. Change gear lathes using half nuts for feed (Workshop C series) typically include some fairly large transposing gear ratios to get the fine feed down to a nice level. Stan (6486)
Alan It looks like the mid-1950's lathes larger than 10" used a ratio of 1:3, not 1:4 as Stan's older lathe did. My 1958 catalog has a print of the gearbox index chart for the 13" and larger lathes, and the ratios are very close to 3. Thus a thread setting of 80 TPI (equals a thread pitch of 1/80 or .0125") shows a feed rate of .0042"/Rev. when power feeds are used rather than the half-nuts, in this case a ratio of 1:2.97. Several other settings produce ratios slightly above 3. This comes from rounding the exact movement per spindle revolution to 4 decimal places. In the newer lathes the index chart shows both the TPI and the feed rate separately, so you don't need to do the above math each time. By the way, the power cross feeds are smaller for the same setting, by another factor of about 2.5. Thus in the above example, a setting of 80 TPI would provide a power cross feed of about .0017"/Rev. This isn't shown on the chart, you need to divide. Frank (6488)
I'm pretty new to this forum, but the few days I've been following have given me some hope with the problem cutting threads with my 9". Don't know what model to call it as its an A C combined. From what I know, it started out as a C with a quick change added. A "few" other unknown worn parts were supposedly changed. The problem is when cutting threads, after 2nd or 3rd thread it starts gaining and the nut or whatever will only travel these couple threads and stop. I've tried 6 or 8 comb and 13tpi is only one that will come close to cutting right. I have a SB parts book and apparently all gears are right. The bed s/n is 99834, but no idea on what the QC is. As you can see this is a pretty old lathe and it shows in places. The lead screw out of the QC has about 1/4 to 3/8 turn slack/slop, could this be some of the prob? Seems that i can hold the hand wheel on apron and keep this slop out, still gains on me. Was there a gear spec change somewhere through the years and maybe I've got to much age difference between added QC and orig bed, apron, headstock, etc? I've gotten used to this ole boy and can easily turn out the type work i do even with the wear, beside I like the dang thing! bill (6943)
I thought I had a similar problem but it turned out that the compound was walking allowing the threads to not cut as deep as where I started. Nut would bind before the male threads got to the back side of a nut when I tried to put a nut on the newly threaded shaft. Lew (6944)
Bill What gear pattern setup do you have on the end. what stud gear are you running? By the way, on the A conversion, did they also use a power crossfeed apron and carriage? Clint (6947)
You aren't describing how you are set up on threading. Set your compound to 29 1/2 degrees. Make sure the bit is centered. I take it you have a threading dial on your lathe. The marks there are for reference engagement. As a rule even threads on any mark. Odd threads (13 tpi) on even marks and 1/2 threads on only one mark (choose a mark say a number is best and keep the engagement only on this mark). For the first pass you can take about a .020 cut, then a .010 cut after that only .005 and .001-.002 on the last couple of passes. Use thread cutting oil. You need to set the zero on the cross feed dial at the start. Then make you advancements with the compound slide feed. Don't know if this is the problem or if with the machine as you indicate. Tom (6956)
Guess I was a little vague on describing thread cutting prob. Am following SBs procedure for cutting threads as laid out in their little booklet "How to run a lathe". (great little book!) And, yes, I do have a threading guide. I also check with thread gauge and there is where the gain/separation is really apparent after 2-3 turns. Gears on end are as shown in SBs parts booklet. 20 tooth stud and 42 tooth special for the double tumbler gear box. As for the apron/crossfeed, I don't know if changed from A model with QC, but suspect not, as "few" other parts changed were implied to be small. Were there diffs in A C aprons? bill (6963)
Bill, Not quite sure what you are asking, but just as a general refresher for all, here's the way the gears are supposed to be from the end of spindle to the Q/C gear box (see attached picture). From the reverse tumbler off the spindle we have a 20T (normally) or 40T (optionally) stud gear on the top of the stud gear. From that we go to the 80T idler gear. Finally we have the 56T gear-box input gear. The un-used stud gear (typically 40T) is stored on top of the 56T Q/C gear. Paul R. (6977)
I thought the 42 tooth screw gear was a special, to be used only for cutting 27 tpi [like for 1/8-27 pipe threads] Standard screw gear for a double-tumbler QC box on a 9 or 10K is 54 tooth. (6980)
Sorry guys, I'm having to many senior moments lately. The gear setup is right, 20-80-56. My computer is a long way from the shop, so I was reading straight out of SB book instead of looking at my actual gears. Also, if I would have paused for a moment I would have realized about the apron having clutch and power feed (mine does) with a QC box. Thanks for the nice pic Paul, that sure will take the mystery out of what its supposed to look like. (looks just like mine) Maybe I will finally get all the info gathered up and we can get an answer. Seems you guys are headed the way I've been leaning for the problem, a wrong gear somewhere! Like maybe just one tooth? I sure haven't found it, hope maybe someone will come up with the answer. bill (6983)
Bill, What do you mean by "it starts gaining"? Do you mean the threads are not equally spaced? If this is the case, then there is something in the drive train that is slipping or else you haven't taken up all of the leadscrew backlash before the cutting tool hits the work. This is the reason I asked if you were using the half nuts and not the clutch. It may sound silly but I remember a thread (pun intended, sorry) where someone was threading with the clutch and guess what, it slips when the load gets high. It also occurs to me that the tool could be slipping in its holder or even the chuck if it wasn't properly seated on the spindle. Glen (6984)
Screw Thread Transposing Charts
I'm looking for a transposing chart to cut inch threads from a South Bend lathe equipped with a metric QC box. Can anybody help? For those interested in such issues, I'm attaching the transposing chart to cut metric threads from an inch QC box. Anthony (8002)
I don't have the actual chart from the machine but I do have a picture in the 1939 catalog showing the chart with gear combinations for ENGLISH SCREW THREADS using metric pitch lead screw and English transposing gears, for the 9 inch models. Email me offlist if this will help you - I can shoot a photo and send it fairly easily - it is only about 1.5 in by 2.5 in. in the book so may not be suitable for a really large blowup. Can scan in higher resolution and send later but that will take a day or so. (8007)
I've received several scans of SB charts for lathes with 8 TPI lead screws, both with and without QC boxes, to cut metric threads. I've also received a chart for SB changegear lathes with a 3 mm lead screw to cut inch threads. What I'm looking for is a chart for SB, Boxford, Hercus, or similar lathes equipped with a metric lead screw and QC box to cut inch threads. Even though it wasn't what I was looking for, I want to thank those who sent me the "wrong" charts, your efforts to assist *are* appreciated. Anthony (8015)
If I understand you correctly, we already have it: http://groups.yahoo.com/group/southbendlathe/files/Techinfo/9inchmetricgearing.jpg  which includes the chart for cutting English threads with the metric leadscrew and 127/135 transposing gear and the opposite setup with 100/127 gear. The conversion math is simple: (mm thread setting on gearbox) * (127/135) * 25.4 = TPI. I think I wrote that right, but please somebody double-check me. Lurch (8023)
The formula at least needs an inversion, since metric threads are pitch in mm (i.e. mm/thread), while English are threads per inch. So the form has to be: mm thread setting on gearbox = (constant * 24.5 mm/inch)/(threads/inch) Having said that I can't make the ratio 127/135 (or 135/127) work out nicely to an inch thread for standard metric pitches, so this needs some more work. In any case the solution will need a range of stud gears, for the same reason that a range of stud gears are required going the other direction. Frank (8028)
These are for inch Model B C and for metric Model B C. And I have the chart to transpose inch Model A to metric. What I'm looking for is the chart to transpose metric Model A to inch threads. the conversion math is simple: (mm thread setting on gearbox) * (127/135) * 25.4 = TPI. I think I wrote that right, but please somebody double-check me. Actually you got that wrong, it's /25.4 instead of *25.4 and it equals pitch. You have to invert to get TPI. So let's try it: 3 mm x (127/135) /25.4 = .11111111 = 9 TPI (not bad). 2.5 mm x (127/135) /25.4 = .09259259 = 10.8 TPI (not very useful). 2 mm x (127/135) /25.4 = .074074 = 13.5 TPI (well 1 mm would give 27 TPI). Let's try for 24 TPI: 1.1 mm x (127/135) /25.4 = .0407407 = 24.5454545 TPI ?!? 1.2 mm x (127/135) /25.4 = .04444444444 = 22.5 (not much help). How about 20 TPI: 1.3 mm x (127/135) /25.4 = .0481481 = 20.76923 TPI 1.4 mm x (127/135) /25.4 = .05185185 = 19.285714 TPI So, you see, by accident you will run into a *very few* examples that will work, but basically you normally have to select a particular pitch, then, according to a chart, change either the screw gear (the input gear on the box) or the stud gear to get a precise and predictable inch pitch. While I haven't seen the metric A to inch pitch chart I assure you it exists. I've been told it's *very* hard to find. So far that's proving to be true. As I said in an earlier message, I appreciate the efforts that various people have made to assist me in this matter, even though on this point the efforts haven't paid off. It may be that in the long run I'll have to work out the chart myself which is complicated by the fact that, when in direct drive (8 TPI for inch or 3 mm for metric) the drive ratio through the gearbox is *not* 1:1. I was hoping to get a copy of "the official chart" because some people get nervous when you provide them a "non-official" solution. Anthony (8033)
You're right. It's apparently not an 8mm pitch leadscrew at all. This from Tony Griffiths' website: "Metric threading Model A lathes with a 6 mm pitch leadscrew and a screw cutting gearbox had a standard ex-factory drive train consisting of: 20t, 45t, 50t and an 80t idler. To convert this gearbox to cut English threads the following gears are needed: 18, 22, 26, 38, 54, 64, 88, 135/127 compound and a 48/24 compound." Oh, boy, is the math on this one going to be a !@#$^ with the possibility of two compound gears in the train at once. (8035)
I have a metric Boxford which is the UK version of the SB. I have a large plate on the base with lots of gears ratios for cutting imperial threads from very fine to real coarse pitches using the 127/135 compound. I'll copy the details and post if people would find it useful. David (8040)
That would be very useful. I think we've established one could drive themselves quite daffy trying to guess. Lurch (8042)
Frank writes: Having said that I can't make the ratio 127/135 (or 135/127) work out nicely to an inch thread for standard metric pitches, so this needs some more work. It's a mystery to me too, but if you take the metric Model B C chart and do the multiplication on several pitches it actually comes out precisely correct. Anthony (8052)
David writes: I have a metric Boxford which is the UK version of the SB. I have a large plate on the base with lots of gears ratios for cutting imperial threads from very fine to real coarse pitches using the 127/135 compound. I'll copy the details and post if people would find it useful. Yes Please!!! While you're at it, does your lathe have a 6mm, 3mm or other pitch on the lead screw? I noticed Tony's SB web site states the following: Metric threading Model A lathes with a 6 mm pitch leadscrew and a screwcutting gearbox had a standard ex-factory drive train consisting of: 20t, 45t, 50t and an 80t idler. To convert this gearbox to cut English threads the following gears are needed: 18, 22, 26, 38, 54, 64, 88, 135/127 compound and a 48/24 compound. Can you confirm these tooth counts on your Boxford? Thank you so much for your offer to assist. Anthony (8054)
Lurch and Anthony I think that starting with the lead screw pitch for a lathe with a QC gearbox only confuses things. Without any gear changes, a lathe with metric leadscrew and QC gearbox choices will cut the following TPI: TPI = (25.4 mm/in)/(pitch setting in mm on the QC box) This is just turning mm into inches, and inches/thread into threads per inch. Those aren't real interesting TPI values for most of the standard metric pitches (like .75 mm, .8mm, 1 mm, etc) Adding a 135 driven gear coupled to a 127 driving gear in the gear chain gets us: TPI = (25.4 * 135/127)/(pitch setting in mm) = 27/(pitch setting in mm) This almost has to be the way the 135/127 gear is used, since 127 is conveniently 5 * 25.4. So 1 mm pitch gives us 27 TPI, and none of the other reasonably standard pitches give us anything useful. If we use a stud gear other than 40, we get: TPI = 27*(40/stud-gear)/(pitch setting in mm) This still doesn't help a lot, since 27 = 3*3*3, so almost nothing cancels. By any chance did the metric leadscrew lathe come with something other than a 40 (or sometimes 20) tooth stud gear? It sure looks like things would be easier with a 140/127 transposing set (yielding TPI = 28/pitch, with the standard stud gear, and lots of useful combinations). We may be forced to wait and see how South Bend actually did it. Frank (8059)
The standard setup on South Bend and Boxford metric Model A lathes used either a 20 or 50 on the stud and a 45 on the gearbox. (80 idler but anything that fills the space will do.) I believe the above also applies to Hercus and other South Bend clones but I haven't verified that. Apparently South Bend metric Model As used a 6 mm lead screw, Boxford, Hercus, and probably other SB clones used a 3 mm lead screw. Anthony (8085)
My model "C" is up and running. I have turned a few test pieces and checked them. Everything seems to be in good working order. I turned down a piece of stock to.492" (matching a 1/2" bolt I had laying around), put on the 32 and 52 gears, per the chart, and started in. First pass was good. My question is, how do you return to where you started to make the next pass? My lathe has no threading dial ( if I am correct in assuming that is what I am missing), so how do you index with one , if you have one? What do I need to do threading correctly? Rich (9174)
Rich, Without a threading dial, you have to leave the half-nuts engaged. What you do is to make your pass; withdraw the threading tool and stop the motor; reverse the motor and let the tool back-up to the beginning of the cut; then set the tool for the next pass. While doing all this, the half-nuts stay engaged all the time. As you can see, this is a slower process and is harder on your half-nuts. Also, it makes threading to a shoulder a real challenge! I would get a threading dial when you can. It will save a lot (including your sanity). Webb (9177)
Rich If you d like to make a threading dial there s an article in the files section with plans. Very handy item to have but tend to be pricey; even on eBay. Lew(9179)
Rich You can also stop the spindle by releasing the belt tension. This typically causes the spindle to stop faster (less inertia). Once the spindle has stopped you can retract the cutting tool and reverse the motor at your leisure. Keep track of how far in you got by the horizontal feed dial or compound feed dial (set at 29 degrees), so you can feed a deterministic further amount on the next cut. Using the belt tension release you can in fact thread to a shoulder (the thread dial doesn't make this any easier). Frank (9180)
Rich, if you do not care what type of threading dial you have, I bought one off e-bay for $5 fits a 6" atlas which also has an 8 TPI leadscrew. I was not going to pay big bucks just to have an original southbend part as my lathe never came with one anyways. Scott (9181)
I assume you are referring to a "real Atlas Atlas" not a Craftsman or an AA109 which are frequently called Atlases. I could definitely use a threading gauge for my SB 9" C and have several 6" Craftsman lathes but the tpi on them is not the same as the SB. (9186)
Rich, It could have been from a larger atlas, but it is definitely from an atlas, if you want a picture just let me know. Scott(9193)
Frank writes: Using the belt tension release you can in fact thread to a shoulder (the thread dial doesn't make this any easier). Actually, with some provisos, it does. If it's acceptable to have a run out groove, and if you can reliably open the half nuts at precisely the same point of traverse, when you open the half nuts without retracting the cutting tool you will simply cut out a relief groove at the end of travel, the groove having the same form as the thread but without a helical advance which is what turns the groove into a thread. To look at it from another perspective, the run out groove would be a screw thread of zero pitch. Can this be done? Of course!! Hardinge, Monarch, Pratt Whitney, and many other lathe makers depended on a variation of this concept. Hendey did it a century ago. In their cases they disengaged a clutch in the screw cutting gear train to stop the advance of the cutting tool. I know this appears to go against everything you've been told (never disengage the gear train) but they used a forward-neutral-reverse-mechanism in the screw cutting train that ensured picking up any pitch thread, no matter if it was in the same system as the leadscrew (let's suppose inch) or any other (let's suppose metric). If you can reliably pick up the thread you can afford to "break" the gear train or open the half nuts. The above concept is superior to opening the half nuts because it allows picking up any thread, independent of its type, but as long as you stay within type (inch-inch, metric-metric, etc.) opening the half nuts at a precise point in the traverse will serve as well. All you're really interested in is stopping the carriage traverse at a precise point and being able to pick up the thread for the next cutting pass. The threading dial, which was the starting point of this monologue, enables you to pick up the thread after opening the half nuts. If you want more information on the subject read "Screwcutting in the Lathe" by Martin Cleeve. And there have been articles on knock out mechanisms for the half nuts in ME and some other home machining magazines. Anthony (9202)
Scott writes: if you do not care what type of threading dial you have, I bought one off e-bay for $5 fits a 6" atlas which also has an 8 TPI leadscrew. Incorrect, the 6" Atlas (as well as the 6" AA) use a 16 TPI leadscrew. The gear on the 16 TPI threading dial has half the pitch required for the South Bend leadscrew. Anthony (9203)
Screw cutting at 25 degrees
I've noticed that the majority of users use 27 1/2 or 29 degree setting for the top slide when screw cutting. After reading George Thomas's excellent book 'The Model Engineers Workshop Manual' I followed his recommendations of using a 25 degree setting. He noticed that sometimes the trailing flank was scored. The reasons were found to be that on some materials the trailing edge was scored by the springy chip being deflected into the trailing flank, as there is no further cut on that flank the scoring remains. By changing the angle to 25 degrees in addition to the main cut there is also a shaving cut of the trailing flank. As an additional bonus instead of the depthing having a multiplier of 1.127D ( approx 1 1/8) the new multiplier is 1.1. Thus a depthing that say requires a 0.08 actual now requires a movement of 0.088 on the top-slide. Bernard (9282)
Bernard; Was this for Whitworth (55 degree) threads? The 29 degree setting does make a shaving cut on the trailing flank for 60 degree thread forms, but would be completely clear of the trailing flank in the case of a 55 degree thread form. Stan (9285)
Good point Stan. It would vary from thread types as per the angle of the thread. Divide the thread angle by 2 then subtract a 1/2 a degree or 1 degree. So for the 60 degree American thread is 60/2 = 30. 30-1/2 = 29.5. I personally don't think this is the problem. I've cut threads with a straight in feed. You have to do this on multi-lead threads. At least how I set it up. The threads looked ok. Since he's cutting cold rolled (probably 1018) its not as much of a factor. Still, he should set the compound correctly, just to minimize the possibilities. I think the main problem is with the cutting tool. Frank, I got your address. I might check tonight to see if I have a threading tool to spare. What size of shank do you use? I might be able to spare a HSS. Tom (9286)
One more thing, Frank, check the tool over hang. You want this as short as possible. Especially with threading. Now being a beginner, you might ask 'what is tool over hang? Well its the length from the tool post to the tip of the cutting tool. Hope its clear and do this with all tooling. Are you using cutting oil? Get some from the local hardware store. It does help. Tom (9287)
Stan, You're quite correct, this setting is for Whit threads. I keep forgetting that UNx threads had a different form factor.  (9288)
Threading question
Lacking a thread dial for my 9"C, is it possible to reverse the motor and back the tool out of the thread it has just cut to index for another pass? I have a reversible motor I can mount to my countershaft that I thought about using if this is possible. Rich (9938)
Rich, Reversing the motor to set up for the next cut is the one thing that ALWAYS works. Glen (9941)
That is the basic procedure in "how to run a lathe". (9943)
Rich Yes, but DO retract the tool from the cut first as the slack in the halfnuts will shift the tool over on reverse and destroy the good thread. Also, threading to a shoulder is nearly impossible as the motor and drive will take a few extra revs to stop before it's ok to reverse. Working close to the chuck is out of the question. You really ought to plan on getting the threading dial. Learn to use the topslide (compound) set to 29 degrees so that the cross-slide is always set to zero for each cut. The topslide is then only used to set the infeed cut. Also easy to remember the last setting. When you get good at threading, stopping a cut at a given point by whipping the tool out of the cut before stopping will make you shine. RichD (9946)
Rich, use the belt release to stop the spindle. Without the angular momentum of the 1750 RPM motor, the spindle will stop quite quickly, especially at a low backgear speed. The spindle/leadscrew relationship is maintained, so this works fine for threading. This works without a threading dial (stop the spindle with the belt release, reverse the motor at your leisure, re-engage the belt). It is also a good way to stop at a shoulder even of you have a threading dial. Frank (9949)
Rich; No problem doing it this way, without a threading dial or for certain weird threads that don't map to the threading dial it's a standard way to do things. Just be sure the lathe stops all the way before reversing and your speed is low enough the chuck isn't inclined to unscrew. Done threads this way quite a few times. Stan (9951)
I've done it that way at that day job many times. On most lathes it's the only way to cut a metric thread, and usually easier then dealing with the transposing gears to get the exact pitch. we have an Italian lath at work and it's set up with an American lead screw and ratios so when we do metric threads for the Japanese injection mold machines we have, that's how we do it. Kerry (9967)
Threading on 9 A
My " How to run a lathe " does not say. Do you use your back gears to thread? I've tried everything I could think of and is still not coming out right. Have read all kinds of books, and none of them say. Could anyone give me i.g. on this machine to try? Used thread dial, and will not cut in the same place. Rob (10413)
Rob, A few things that can mess you up: Have the apron feed selector lever in the middle position. This disables the power long- and cross-feed and allows the half-nuts to engage. Use the threading dial if you have one, else leave the half-nuts engaged and just stop, back out the cross, and reverse the motor to get back beyond the starting point. When threading, you are using the HALF- NUTS lever (pull up to engage), not the power-feed star-knob! Don't ask me how I know ;-). Make sure your lead-screw and half-nuts are in okay condition. At this point you should be able to chase the same thread. If not there is slipping between the spindle and the lead-screw. After you are chasing threads, you should be able to verify the TPI by lightly cutting the surface and then inspect it with a fish-tail thread gage. Paul R. (10415)
Yes, use your back gears. Run real slow. On brass and aluminum (which is mostly what I use) I use slowest speed and lots of cutting oil on brass and kerosene on aluminum. Feed with the compound properly set. Frank (10416)
Like Frank said, use the back gears. This is especially crucial on coarse threads. The back gears have nothing to do with the rate of feed per revolution of the spindle, it just makes it easier to start and stop at the right place when the spindle is turning slower. It is also helpful to use the belt tensioner to stop as you don't have the rotational momentum of the motor and pulleys to keep the spindle turning. Unless I am making a very long thread, I always reverse the motor to start a new cut. I learned to make threads on a Sherline with no half nuts or thread dial. I guess I just haven't learned to trust 'em yet. Glen (10417)
Gentlemen Half the battle with threading and thread dial indicators is visualizing WTHIGO. Many years ago I was given the following exercise which helped a lot:- 1) Set up the lathe so the cutting tool runs away from the chuck. 2) Use a bed stop to fix the start (chuck) end of the thread. 3) Fix a piece of paper firmly around a reasonable size mandrel and mount in chuck. (Make sure the paper can't slip and rotate round the carrier) 4) Replace cutting tool with a sharp pencil. 5) Put a temporary rotation position mark on the chuck (use tape, spirt pen, wax stick or whatever you have) 6) Set-up to cut a thread of the same tpi as the leadscrew and lowest backgear speed. 7) Experiment taking care always to start "threading" with the saddle hard up against the stop. Replace paper and sharpen pencil as required. Marking the chuck and always starting from the same point on the bed makes it easy to see how the thread dial "calculates" the relative positions of chuck (rotating) and tool (longitudinal). The pencil marks make it much easier to see what happens when the half-nuts are engaged in the wrong position. Cutting away from the chuck means that you don't have to worry about dropping the nuts before a smash-up. Once you have got things straight using a fixed starting point, try starting a bit further down the bed watching the rotational position of the chuck and the thread dial position at the half-nut engagement points. It should soon become clear how the thread dial automatically compensates for saddle offset allowing the chuck to turn further so that the tool is still in register with the thread despite starting off further down the bed. See if you can use different dial graduations and still get the right engagement point. When the thread tpi matches the leadscrew there is plenty of choice! Now try it with different threads (hint:- the relative multiple between leadscrew tpi and thread selected has an effect on which combinations of graduations it is safe to use). An hour or so of playing should make clear what is going on understanding the mechanics is then quite simple. If you really get stuck (I did!) drop the belts and turn the chuck slowly by hand which should make it really clear how the dial graduations select the correct tool to thread registration when the half-nuts are engaged. Clive (10419)
Clive Absolutely excellent explanation of how to do it for good results. Now here is one that belongs in the FAQ. JWE (10421)
This is exactly why I most often reverse the motor to start the next cut. I assure you that I am not stupid but I choose to think hard on those problems which require my intellect and not those on which the flipping of a switch will make go away. Glen (10434)
Rob, As I re-read your question, it dealt specifically with the back gear. The normal gearing is set so the motor spins the jackshaft and then that in turn spins he lathe spindle which in turn spins the gear train. with the back gear disengaged, the lathe is running full speed or high gear. the gear train starts on the back of the spindle and runs through some different gears. on a Model C or Workshop, you must manually change the gear ratio to get the thread correct. the label on the gear cover would indicate what the proper gears to be used are. The back gear comes into play as regards to lathe speed. I call it low gear. the motor spins the jackshaft which spins the step pulley which spins the back-gear which spins the spindle. everything is in slow motion, but all the thread and feed ratios are unchanged. Of course you need the stack of gears to know change them. Also as was pointed out, the half nuts are the ones to use, not the feed lever. And regards the thread dial, always start at 1 regardless where you need to put the carriage or thread pitch and you will find it doesn't matter for the rest of the thread pitches, or leave the half nuts engaged and feed the carriage back and forth by reversing the motor. Dave (10443)
Now that's what I call a fine thread
I had always considered the ultra fine thread tpi settings on my Heavy 10 gearbox (max tpi is 480) a pure side effect of the fine feed provision and merely marked up for the sake of completeness and possible satisfaction of some obscure American humorous imperative. Not anymore though. In the April issue of Laser Focus World Azeer Enterprises are offering 200 tpi adjustment screws and micrometer heads. That's 5 thou per rev. And the thread depth is probably less. How do you cut a thread that fine and for that matter manage to start the nut without cross-threading the beast. I've known machinists who would consider that an acceptable finish for non precision work! I presume that no one has screw cut a matching nut and stud at 480 tpi. Or have they? Clive (10869)
I think that first, I would consider rolling said thread, and I would definitely put in a land to allow the parts to align before the threads engage. I am impressed with a 0.005 " feed per rev. that means the thread width must be less than half of that or 0.0025" and that thread depth is probably also less then 0.005" one bad thing would be to have a dull cutter and try to run it a second time to clean it up ! Dave (10878)
My SB9 has always been set up with the following: A 105 tooth turning gear, engaging a 2:1 reduction gear, engaging a 6:1 reduction gear, driven off the spindle (24 tooth). This gives a feed of 0.0024" per turn of the spindle. I use this for feeding not threading. Jim B. (10880)
Thread size
What thread type would have been used for the tapped holes in a 1944 10in heavy. Being an Englishman in his 30s I've only ever known metric. (11309)
Your best bet is to order the parts manual from Rose at LeBlond. Immediately after that go to the group site and print off the SB publication that gives the common fastener size by SB part number used on the machine. I think most have a common English size equivalent, it was most helpful to me. At one time the screws and bolts originally on the machine were hardened and, I think, blued. Is non-metric hardware even available in most UK hardware stores these days? Bill (11399)
I've heard of metric threads, but am not sure how they differ. Being an American manufacture of the pre-metric days, I would be quite sure they are standard SAE screws. Measure the OD and convert to inches and then count how many threads there are in one inch. the shopswarf index lists the different threads so you can look up the sizes. in the States, we use the outer diameter of the major diameter (converted to a fraction or an inch) for the first number. 0.5 inches is 1/2 inch. then the number of threads per inch as the second. if there were 13 threads per inch the bolt would be 1/2-13 then the length of the thread diameter. so if the bolt were 2 inches long, the head would add another 1/4 or so to the overall length. so a 2" long bolt would really be about 2.25 or so long. Not sure if that if any great help, but if you run into American threads often, look for a thread gauge. probably less than 20 pounds. Looks kinda like a set of feeler gauges, but with teeth. Dave (11400)
Threading question
How do you consistently stop at the same place for internal threading? I don't like to machine a 'finish slot' at the end of the internal thread for reasons of integrity; if the wall thickness is thin to begin with, I figure having the slot there will make it weaker. I've been getting by with just idling the threading bit at the end of the cut, and trying to bring it to a stop at more or less exactly the same place... but noticed that if I mistimed the feed disengage by a little bit, the tip of the fragile carbide threading bit will get broken off as it hits the 'fresh' uncut tube section. At first I tried watching the cutting bit, as you do on the outside cuts; but it's too difficult leaning into and over the ways since my machine is large and thick and the ways are right around elbow height... now I just set the carriage stop on the ways at the end of the cut, but don't lock it down; it's only there as an indicator to tell me when to disengage. I use super low speed to allow me time to disengage quickly; maybe 25rpm or so. Any other ideas? Or am I completely off base? Also, I've noticed that when using the normal tables, for instance the Atlas Manual of Lathe Operation, Table I, Depth and Double Depth of Thread for National Form and Vee Form tools... my numbers don't seem to be anywhere near what the manual indicates. For instance, at 32tpi, the depth of the compound feed (set at 29 degrees) according to this manual should be .027" for a Vee Form tool... but when I true up a cylinder and do an actual cut, I've noticed that I have to feed the compound something closer to 0.85" to get a complete "V" cut (not a 75% finished NF semi V)... why such a huge difference?? I've indicated my compound and it's turning in the proper amount, so my actual figures aren't off. (14259)
Actually, the part should be stronger with the slot cut into it. Threads are a big time stress raiser. If the material is too thin for an under cut, then its way to thin with threads. The thread depth isn't much less than the undercut. Also put a 45 degree internal chamfer. It helps keep burrs on the inside from happening. Tom (14261)
You don't just stop the thread hard. You can do a few things. You can use a hand crank on the spindle and when about 1/8 turn from the end of the thread move out of the cut. You could run the lathe in reverse and cut out into open space. You could use a tap :-) or make a piloted tap if this is a special application. The run out area isn't going to weaken the tube much more than the threading will, provided you make sure you radius the corners to avoid stress risers. Stopping the V thread abruptly is going to give you the worst combination of stress risers, with two sharp corners plus a sharp point where the other two risers meet. You can reinforce the area where the internal threads end by leaving a bit of material turned to minor diameter of the threads on the piece that screws in. If it fits well within the tube, this will move the bending into the part of the tube that is full thickness. As to depth of cut: Sounds like you are not accounting for a few things: The depth of cut will be equal to the indicated depth on the compound times the sin of the compound angle. Add in the variation from sharp to NF form and you get pretty close, assuming that "0.85" is a typo, and that this number should be "0.085" 0.085 inches * .485 = 0.041 inches 0.0412 inches * 0.75 = 0.031 inches. The remaining 4 thou is probably thread roughness, backlash, tool spring, variables in how you measure the cut thread, the usual shop gremlins. Stan (14262)
I cut inside threads on the back side of the part with the tool held upside down. You can see what you are doing without leaning over the lathe and getting caught in moving parts. Glen (14263)
Stan, those are excellent suggestions. Thanks. I didn't really think of reversing the lathe, but I have a gear drive and at that speed it sort of comes to a stop very slowly; I don't like reversing while it's still moving and although there is a large handle for disengaging and braking the spindle, I haven't yet tried this in connection with any threading operation as I tend to not want to move anything until I'm satisfied the thread's complete. I'm sure you know the feeling. I'll experiment and see what happens. I do use a chamfer, but I've tended to use a 60 degree included angle instead of 45 degrees (makes it 30 actual degrees) as it's convenient... it's the same angle as on the indexable cutting bits. Is 45 significant for some reason? With respect to my odd numbers, you're right; it was a typo, supposed to be 0.085" ...but the sine portion is off. I took that into account, as the Atlas table has a normal column for referencing the pure cross feed number, and another column for use with the cross feed when set at the normal 29 degrees, which takes into account the angle. I know what you mean by slop, but this goes way beyond and I still can't figure it out. walt (14264)
Or cut them on the back side with the spindle in reverse. You need a reversed threading bit to do this. Ed (14265)
And preferably a *NON* threaded spindle nose (i.e.. D-Series, A-Series or L-series). Scott Logan (14266)
I always make the bottom relief groove, only as deep as the thread. Set up an indicator on the bed to follow carriage movement and set to zero at the beginning point in the slot. Yes, you will have to run in reverse as the tool has to be at the rear side of the cut to get a RH thread from in to out. Release the belt tension before starting the motor and ease the spindle into motion for a cut. Or use a front facing tool and slow speed watching the indicator for when to kick out the half nuts. Still with a good bottom groove to stop in. The depth of cut is highly dependant on the width of the tool tip. Getting this exactly right is not practical, so I always use a gauge piece to test the "class of fit" I want. RichD (14267)
Cutting threads without a thread dial
How do you cut threads without a thread dial? I've seen this come up a few times lately. Here's a trick an old-timer taught me years ago. Set the thread at the q/c box or install change gears for the required number of threads, set compound at 30 degrees, "zero" the crosslide, all like you would with any thread. Now move the carriage stop to the tailstock side of the carriage (if cutting right hand threads). With the stop in contact with the carriage, lock it down. Now engage the halfnut and make the first pass, disengage the half nut and pullout at the end of cut. Return the carriage to contact the stop, reset the crosslide to zero and set depth at the compound for the next cut. Engage the halfnut again and it will connect to the leadscrew at the exact location as the first cut, continue this until the threads are complete. Try this, it really works. Rick (14510)
Hey thanks, dude when I get my compound set up and a toolpost to where I can try that I surely will. (14511)
Rick, that only works for threads that are devisable by the leadscrew pitch and the stop is not necessary, just convenient. Set the top slide to 29 deg. for a better finish. I single point thread thread often, inside out, L R hand. RichD (14516)
Rich The stop is more than convenient, it sets up a relationship between the halfnut and the leadscrew. If you have a thread dial, try my method and it will only let you catch the leadscrew on one graduation on dial 1, 3 ect. This way you don't have to worry about if the thread is a multiple of the lead screw thread. 29 degrees works great the tool just rubs on one side and cuts on the other. My method would work on left hand or right hand, you would have to put the stop on the appropriate side. Rick (14527)
Its fairly obvious that this particular method is not infallible for all possible thread pitches but I don't know whether any of the pitches for which it fails correspond to practical threads that are actually used for anything. Personally I'd be suspicious of any pitches divisible by three but, without working it out, that may be pure "off-the-cuff" prejudice. What will make it infallible is to put some sort of witness mark, e.g a paint splash or piece of tape, on the chuck and only engage the half-nuts as the mark comes towards you past a suitable reference. Were I to do it I'd set things so I engaged the half-nuts as the mark comes up to the bearing cap bolt. This manner of working fixes both the chuck rotation angle and tool point longitudinal position at the moment of half nut engagement. Effectively doing this is the same as using the old Exe lathe with its single point dog clutch to engage the lead-screw which, I am given to understand, is infallible at all pitches. Marking the position of number 1 jaw on a three jaw SC chuck is a good idea anyway. If you have to replace work in the chuck its more likely to go back concentric if you align it with the same jaws and use the same pinion to tighten up the chuck so a ficidary mark is a great help. If the chuck is well past the first flush of youth using different pinions for tightening can make a big difference. I had one that would co-operate only when number 2 pinion was used. Some lucky folks have the jaw numbers stamped on the outside face but mine have all been numbered inside the jaw slots. Clive (14542)
I don't see what the big deal is. There are plans to make a thread dial in the files section of this site. The methods sound a little like the "mousetrap" game my daughter had years ago. I use a thread dial from a Sheldon lathe I picked up very reasonably. JP (14553)
Rough External Threads
Why? I'm following all the directions (I think)! Doc (15900)
This is a case where a picture is worth a thousand words I think, you got a digital camera? I'm no expert, in fact I never tried to cut threads yet with my lathes, might be able to help though. (15902)
Doc, are you closing your half nut at the same place on each cut? Do you have a thread dial on your apron? If so start each cut on a line or number on the thread dial. If you are not doing this it could be what is causing your problem. Duane (15903)
My first try at threading was not my best either. Most failures are due to inattention or accumulated error. Start with a sharp tool. Be sure it is on or a touch below center. Three degree rake. Be sure your not going to fast, put her in grandma, (back-gear). Use light cuts with oil. Each cut should be no more then .005 per pass. Every 3rd pass is a spring cut. Toward the end of the job dial straight in .005. This cleans up both sides of the thread at the same time. Makes the threads look professional. I leave my threads a bit tight and lap them to an accurate polished fit. This is easily done with a strip of 600 silicon carbide wrapped around a 3-cornered file. This way the nut or mating part has a light drag for a fit. Nut'in 2 it! Another way to lap threads to a high finish is to take a nut the right size and split it. Add some 600 clover-leaf and place a clamp on the lapping nut. As you go over the threading job put a slight tension on the nut. It's a cheap shot but it works. As for making shims, I'd get a sheet of .001 S.S. shim stock, cut it in strips and glue them together with some kind of wood glue. Put a 5lb. weight on them for 3 hours. You should be able to peel them back as needed. Experiment with different glue for best results. Finally, a word about the Order of the Great Iron. We are preservationists plain and simple. It is our passion to save these wonderful machines. They are a living history in a world of virtual nothing. We sweat and swear and sometimes bleed as we fix and use them. BUT THEY ARE REAL. As real as the loss we sense each day we go to work and watch the world go to hell on a Pentium chip. Our fathers are dying a thousand a day. That's the rate of death among WW II veterans. Machinists of our kind are not far behind. We have now become nostalgia. Real magic is not a computer. It is what happens when someone runs these machines and makes steam engines, watches or telescopes. We are wizards that dare to dream about how it was. Ron (15904)
Doc: What material are you using? Ron (15905)
I found that if I was running the spindle too slow I got crappy threads. Had much better luck running at pretty much the same speed I'd run if I were doing normal turning. Now Ron has stated to put it in backgear, and it sounds like he has 'a bit' more experience than me (like in I've cut threads all of 3 times, whoop-de doo) so take my advice for what it is - just another thing to try. It also seems to me that after running a nut back and forth on the piece a few times, the thread 'cleans up' a bit. Keep at it, it is very satisfying when it works. John (15907)
Make sure the compound is set at 29 to the right. Use sharp tool, correctly ground, or a formed threading tool. Cutting tool at center height. Feed with the compound, leaving the crossfeed at the same setting for each cut. Use the back gears - slow speed. (very slow for stainless) Engage half nuts at the same number on the threading dial. (Any mark for even threads, numbered mark for odd threads.) Use a good thread cutting fluid. You may make the first couple cuts at about .010, but then reduce the amount you feed the compound. You may be increasing the depth only .001 to .003 for the final cuts. Make your last two cuts at the same setting for clean-up. Jim (15908)
Doc, Crossfeed set at 29.5 deg? Advance cut with the compound not cross feed. Object is to cut one side of the thread not both sides at a time. Larry (15910)
Thanks for all the tips I will retry and recheck everything. I never bothered to understand the gradations of the thread dial and just always engage at a real number not a line regardless of the thread count. The roughness is the same in steel or 6061 I'm using a 60 degree point on a insert tool on a Phase I quick change and using back gears (14 tpi requires the leadscrew run too fast for my reflexes at a regular speed) (15913)
Robert If you are using the chamfering bit that comes with most tool sets it will always make rough threads because it is not designed for threading. The style E tool despite being advertised for threading is not usable for threads finer than about 8tpi. The specific ER and EL cutters will produce fine threads every time. JWE (15915)
Thanks. If you use the ER or EL do you still sent the compound to 29.5 ? (15916)
Robert Yes, or 29 or 30 degrees using a machinists protractor. The most important is the form of the tool that forms/cuts the thread. The E style tool when measured as a threading tool is a 120 degree tool not a 60 degree tool and that is why it cuts lousy threads. JWE (15918)
The ER took care of the persistent rough threads. Thanks (15924)
Threading drill rod?
Can anyone tell me how to thread oil hardening drill rod w/1/2" die? I tried it as is, and I tried heating it to a red heat and slow cooling it but all the die does is grind the end off. It was a good die when I started but don't know about it anymore. (15985)
O1 is a bugger to thread with a die, try putting a chamfer on the rod first and use a name brand, "USA made" sharp, adjustable threading die. Some dies are for rethreading or thread chasing. They are generally non adjustable. Some Asian made dies are made from an indeterminate grade of steel. J (15987)
Thanks JP. I'll try chamfering the end but I don't hold out much hope. I used a craftsman die and it has never failed me before. Not adjustable though. Next time I'll use some other material! (15992)
I forgot to mention the end of the rod should be turned square first, not just cut and the chamfer can be small, 1/2 thread width will do. For 1/2-20 a .025" chamfer will work. The A1 and W1 material is worse, leaded steel like 12L14 works out nicely, for stainless 304 isn't too bad to thread. JP (15997)
Can you cut finer than 160 TPI on a 9" C?
I'm interested in making very fine finishing cuts and would like to "trick" the lathe into moving the carriage at 200, 300, or even 400 TPI. Is this possible with a model "C"? If so, how? Best regards, Keith (16819)
Keith, Really, you need to learn about radiused tool tips. The normal fine feeds should be adequate. If anybody is fussy about tooling marks, that's me. Anything finer requires grinding and polishing. RichD (16820)
You need to keep your eyes open for compound gears and the largest "turning" gear you can find. They do show up on e-bay. I have a 2: 1 and a 7:1 and a 105 tooth turning gear. (These are the old 20 DP however) I have seen similar ones on e-bay. Starting from a 24 tooth gear (the spindle) then you get 105/24*2*7 = 61 turns of the spindle for every turn of the lead screw or 0.002 movement of the tool fro every turn of the spindle. With 18 DP gears (standard for SB-9 after 1936) you could put a 16 tooth gear on the reverse gear drive shaft. However the diameters of the gears are bigger. For the reduction you want you would need to go to a triple compound. You could probably get one more reduction if you picked the steps right. You would then have something like 105/16*2*5*5 = 328. I am just guessing at the 5:1 I am not sure that its available I haven't paid much attention to the compounds on e-bay. I just felt that you might need some room to get the third compound gear in the train. A alternative is to use Boston Gears 20 DP. They sell adapters to make compound gears, see page 16 of the open gearing catalogue. (Remember the spindle and the three gears on the reversing gear assembly are 20 DP only the gear you bolt on the stub shaft of the reversing gear assembly and the drive and idler gears are 18 DP. With the Boston Gear compound assemblies you would need to make new bushings to mount them to the spider. The bushing has a standard ID of 0.4375. Od is 0.625 Could be bored out a bit but I doubt 0.5625 is achievable. Also you would need to adapt the drive gear. Your lead screw is 0.5625 the Boston gear Gears are 0.625. Still if you want all that reduction its worth consideration. My 9" is older and did use 20 DP. I still use them for turning. I am trying to adapt to 18 DP for thread cutting. Jim B (16821)
This brings to mind another question. Has anyone ever cut matching 460 TPI threads? What is the finest matching threads someone here has cut, even if just for the heck of it? JP (16824)
JP, I have single point cut steel .200mm x 120 TPI threads for screws for a model. I still have them. I case you ask, it was not done on a SBL. RichD (16827)
I just went down an looked at the possibility of a third compound. I was able to get the 5:1 ( I said 7:1 its actually 5:1) to drive off the reverse gear assembly. In one position it drives off the button of the 3 gears in another off the middle. I was able to also get the 2:1 on the top arm of the spider to engage the 105 tooth gear without locking the 5;1. That leaves room for a third compound, hung off the bottom spider, but on an extension arm, to give you additional reduction. You would need to rig up an additional to allow the small gear of second 5:1 (or whatever) to engage the big gear on the first 5:1 and simultaneously have the big gear engage the 2:1. Also I think you might need the 20 DP's to fit. Jim B. (16829)
The fine finishing cut is done with HSS and a polished bit. Take the grinding marks off with a hard stone or soft wheel and polishing compound. View the bit under magnification and you will see the grind marks clearly. A polished round nose HSS bit will do it. JP (16830)
My model C chart goes down to feeds of .0021 which unless my math is faulty translates out to 480 threads per inch. That is with at 16 tooth stud gear, 80 tooth screw gear and both the 54x18 and 72x18 compounds. Also available are 200, 240 and 320 tpi. This is with the standard set of gears for a C. Note that the B does not have the necessary gears in its standard set it is missing the 54x18 compound. Actually I have had my C setup in this range for years but I agree that a rounded tool bit is required for really fine finishes. (16834)
The threading chart at the bottom of this page http://www.lathes.co.uk/southbend9-inch/page6.html shows .0021 being 160 TPI with the gear setup you just described (fig. 4). Keith (16841)
The 0.021 feed is through the worm gear and friction clutch in the apron of an A or B model. This doesn't apply to a C model. Glen (16844)
Consider a shaper with a spiral cutting attachment. JP (16859)
You are absolutely correct. I calculated the pitch wrong. (I should not calculate after a glass of wine. There is no need for the triple reduction the double does it fine. Jim B. (16861)
Can anyone give me the parameters for the fine finish tool. i.e., angle of the "V", radius for the front, and the two relief angles behind and below the cutting point. I am assuming this thing goes in perpendicular (with the uncut part of the tool parallel to the bed) at center height on very slow feed (how fast can you get away with with a .005" finish cut), with good chatter free support. I am a newbie who has just learned to do fair roughing cuts. Good at honing tools from woodwork. Steve (16865)
Steve, Depends on the material. For all materials, front and side clearance angles of around 5 to 7 degrees. For brass top rake of zero degrees. For steel top rake of 5 to 7 degrees. For aluminum, top rake of 12 to 15 degrees. A good starting point for tip radius would be 1/16 inch. You can increase this up to the point you start to get chatter. Stan (16867)
Stan has contributed an EXCELLENT write up on tool grinding a few years ago, the info hasn't changed. it's located in the files section for the group. Its definitely a good read. I recommend it as a reference. dennis (16868)
Ah shucks :-) Glad you found it useful, and thanks for the kind words! Stan  (16871)
That is a Model B chart which takes the reduction gearing on the apron into consideration. The C has a different chart as it only has the half nuts to drive the carriage. Therefore the extra compound gear that I mentioned. (16873)
Proper surface speed is also important to a good finish. There are charts in HTRAL and the machinery handbook covering surface speeds for various materials. Finish cuts are typically .001" to .002". For insuring chatter free operation you should have the most rigid tool holder and largest tool bit you can use for the job. JP (16877)
Those turning gears are good, I have a 116 tooth turning gear for my B model. It will put a satin finish on steel even with a regular tool. RC (16885)
Posted today on E-Bay are the following, 2592963342 1:6 108/18 tooth compound gear 2592958249 116 tooth turning gear. Jim B. (16964)
Threading Questions
Is there a quick and easy method of determining the thread depth of different diameters and threads per inch? This is a bit lost to me. I can cut the thread, but don't know when the thread is at the right depth (minor diameter). When using a threading dial on the lathe, if I remove the part I'm threading and decide to go back and thread some more using the same thread I've already started, can it be done? I'm not sure if I'm stating these questions properly. Dave (17135)
If you can get the exact same location as you had you can do it. A very small position error shows dramatically. That is why the short answer is, No. A thread gauge is good for this problem. For common threads you can use a matching nut. Another method is with 3 wires and a mic or caliper. Wires of known sizes are placed into the threads and the overall OD is measured. Its similar to the "rods in the dovetail" and is in the machinery handbook. JP (17136)
Dave, There are different ways to measure threads. The cheapest and curdest is as mentioned with a common hardware nut. A similar approach is with a thread gauge of a go-no go type. Gauges are used for Pipe threads though, but I think you are referring to standard straight threads. Threading micrometers are made to measure OD threads. For ID threads I'd probably use a gauge. They do make ID measuring units, which I haven't used. They are expensive. The micrometer attachments to measure ID threads, haven't worked for me. As far as OD threading mics, they make fixed anvils and replaceable anvils. The fix type are good for a specific thread range, say 0-1 inch diameter and 18-24 tpi. Just as an example. If your needed thread is 3/4-20 (just for example) then said mic would work. The replaceable type, you have a mic of say 0-1 inch or 1-2 inch etc. capacity and you change the anvils to suite your needed threads per inch (TPI). They cost initially more. You would save in the long run as the anils will cost less than buying a bunch of threading mics for various thread sizes. I think there are some sets made in Poland of the interchangeable mics. Should be of very good quality and reasonable price. $169 sticks in my mind, but don't quote me on that. You have to adjust or calibrate the mic each time you change the anvils. If you are only doing one type of thread, then the fixed type should be the way to go. Now if you take out the part you were threading, for whatever reason, you can pick back up the threads. Its really not very difficult. First setup as you would for threading, i.e. feed rate for the specific thread, the threading tool set up to cut. Keep the threading tool on a plane (this is hard to explain) or larger diameter than the threads. Turn on the lathe and take basically a false cut. I.E. start at a distance before the threads, engage the threading lever. Then when the threading bit is near the part, stop the lathe (turn it off). The lathe will still turn a bit and advance the threading tool. After the lathe has stopped, use the cross feed and the compound (set for threading angle ie 29-30 degrees for a60 degree thread), and move it into match the thread groove. Set the dials on the crossfeed and compound feed to zero. Back out the cross feed. Take the tool to the beginning to where you will start your cut and resume to cut threads as usual. I would turn in the cross feed back to the zero point an take a cut and not try and feed in more of a cut on the initial pass. Hope this is clear. Tom (17139)
I thought there was some kind of mathematical formula that would take into account the diameter and the tpi and would give you the depth of cut. I have a thread gauge that I've used, and also have used a nut. Dave (17142)
For "full depth" 60 degree threads you feed into the work a distance 1/2 the pitch. If the thread is 20 TPI, the pitch would be 1/20 or .050 inch per thread. The thread depth would be half that or 0.025. Most of the time threads are not cut "full depth", I think 75% is common, but the depth still should be proportional to the pitch. Glen (17143)
Dave Further to the previous excellent advice don't forget that the theoretical thread depths do assume that you have managed to grind the thread cutting tool to the right profile with the correct width flat on the end. Most mortals, like moi, end up with near enough rather than just right. I find that cutting theoretical full depth turns out about 80% depth which usually works out just fine. Don't forget the spring cuts (successive cuts with the same tool setting). Frequently you will need two or three extra runs to clear right down to the size you have set. This often makes the difference between too tight and too loose! If you are not sure about the thread dial its well worth doing some mock cuts with paper wrapped round a suitable round bar and a pencil substituted for the tool. Then you can see what is happening. Good practice for if you ever do need to pick up a thread again. Clive (17145)
Dave, Just the tpi is all you need. (1/tpi)*.5 = cutting depth Take a 1/4-20 thread and look up the tap drill needed, .201" Ok, so 1/20 = .050" to lathe cut the thread its half of that. Offset your compound to 29 degrees, 61 from the axis of rotation and then its .025"/.875 (sine of 61 degrees or the cosine of 29 degrees) the depth on the compound dial is .029" Take a spring cut or add a bit to make up for tool pressure. JP (17148)
Is there a quick and easy method of determining the thread depth of different diameters and threads per inch? This is a bit lost to me. I can cut the thread, but don't know when the thread is at the right depth (minor diameter). When using a threading dial on the lathe, if I remove the part I'm threading and decide to go back and thread some more using the same thread I've already started, can it be done The book that came with my lathe (Atlas/Craftsman) has tables to show the reading of the cross slide for standard threads, both the absolute measure and the compound reading when the compound is set at 29.7 degrees. And yes you can pick up a thread after removing the stock from your chuck. Get the tool resting in the thread and work from there. That is one advantage of the old type lantern tool post as you can slide the post along the T slot in the angled compound to pick up the thread. John (17151)
Dave, There is. It is small dia=O.D. -(1.299/Threads per inch). Rick (17152)
Correct formula for depth of threads is: .6495 divided by N (number of threads per inch)= Single Depth Of Threads Single Depth of Threads X 2= Double Depth Of Threads Single Depth Of Threads X .5773= Single Feed Depth with Compound set at 30 Degrees I am a machinist by Trade and we cut all Unified National threads with compound angle set at 30 Degrees and tool ground to 60 degree included angle. Ron (17170)
Ron, So to cut a regular set of coarse/fine threads, using your formula's could you tell me what I would do with the formulas to get my total depth of cut. I don't understand the "single depth of threads, double depth of threads, and the single feed depth with compound set at 30 degrees. I apologize for my ignorance. I can do the math, just don't know which formula(s) to use. Dave (17176)
Seems to be much fear expressed by members about chasing an old, used or incomplete thread. Here's what you do in a nutshell. There are two slightly different methods both with the same results. First Method (This is the one I use most often) 1--Set compound parallel to workpiece. 2--Set threading tool using thread gauge or "fishtail" as some people call them perpendicular to workpiece 3--Set Thread gearing for correct pitch, start lathe with cutting tool some distance away from actual cutting surface and engage thread lever at proper spot on thread dial 4--Let machine start to work its way down thread BUT at a distance away from actually cutting. 5--Stop lathe WITH thread lever still engaged( Hint--let lathe coast to a stop and do not stop by trying to reverse spindle as doing that will allow backlash in screw and nut to come into play) 6--Using a combination of compound and crosslide bring threading tool into thread groove until it is touching on all sides (hint--use a piece of white paper underneath thread and threading tool where you are trying to see if tool is touching both sides) 7--Zero Crossfeed dial 8--Zero Compound Dial 9--Withdraw toolbit from thread one complete turn and disengage Split-Nut 10--Reset tool one turn in to Zero Crossfeed setting . 12--You are now ready to start to chase thread at this setting. Depth is increased by turning in Crossfeed dial a few thous at a time until thread is to complete depth or damaged thread has been cleaned up. With this compound setting you will cut on all sides of tool not one side as when compound is set to 30 Degrees. Second Method Basically follow all steps the same as in first method except compound is now set at 30 Degrees. 1--Follow steps 1 through 10 Depth is now increased by moving in Compound Dial a few thous at a time until thread is to depth or damaged thread has been cleaned up PIECE OF CAKE! Ron (17192)
Ron, I don't understand the third statement (single depth of threads X .5773 etc.). Please explain. I am also a machinist by trade ( 22 yrs. so far ), and I'm always up for learning something new. Jim (17194)
That is the amount you feed compound in at 30 degree angle. You would then feed compound in that many thousands of an inch. DO NOT 1/2 that figure as you would thinking that you are taking for example .010 per side for a total of .020. This is Single Depth Of Thread. If you double single depth of thread you obviously have Double Depth Of Thread a figure you will need when doing an Internal Thread to calculate proper bore size. Since my computer skills are so poor I will ask my better half if she will set up a spread sheet with all this info and the calculated figures for threads from 2 to 40 TPI. I will have to do some major whining to get this accomplished. I will post to both this and the Atlas-Craftsman Groups Files if I can figure out how to do that also. Ron (17197)
Dave: Single Depth of Thread is the amount you feed toolbit in measured with compound set parallel with workpiece. Most inexperienced people do not thread this way. They set compound at 30 Degrees. I have cut most of my threads at the parallel setup. Double depth would really be the Minor Diameter of the thread. The other formula with the .5773 multiplier is the amount you would move compound in when threading at the 30 Degree Angle. There is a trig factor involved here so that is where the .5773 comes from. When threading just use the Single Depth of Thread figure or Single Depth of Thread Compound at 30 Degrees. Use The Double Depth of Thread figure to calculate bore for internal thread. Hope this makes sense. Been doing this all my adult life but it is hard to put on paper. Ron (17198)
Dave, Do you have a fishtail gauge, center gauge? Mine has a double depth chart on it. JP (17204)
Ron-- Be assured that I understand all of what you're saying except the .5773 multiplier. The distance the compound travels along the 30 degree angle will be a larger number than if run in parallel with the crossfeed. If the thread depth is multiplied by .5773, you will end up with a smaller number than the thread depth. If thread depth is .032 as in 20 pitch, then the compound travel is .032 / .875 or .037. .875 is a trig function of 29 degrees and is easy to remember as it is the decimal for 7/8ths. I thread with the compound at 29 degrees for threads courser than 12 pitch. For finer than 12, I do the same as you and feed in with the crossfeed, if the material isn't to tough, as some stainless is. I cut some 3", 4 pitch stub acme, 20"s long the other day and there's no way our old machines will stand crossfeed straight in for that. We also cut quite a bit of "mystery metal" in repairing threads in oil field and mining equipment. A work hardened 4140 heat treated drill string tool joint thread can be quite a chore. These are usually 4 or 5 pitch and cut on a taper. Jim (17206)
Ron, I was trying to figure out where you came up with the .5773 number and the only thing I can find is in the use of the 3 wire pitch diameter measurement. Take the pitch length times .5773 and that is the diameter of wire that will rest in the thread and touch the pitch diameter. It is the optimum size wire to use in the measurement. Its also the cosine of 54.7 degrees. What am I missing here, I can't figure out where that number comes from for cutting an SAE thread? JP (17211)
You lost sight of the whole formula though. Tool movement at 30 Degrees is Double Depth X .57773 which will be a larger # than Single Depth. .6495 = S.D. X 2=D.D X.57773= FEED DEPTH at 30 Degrees TPI Ron (17212)
You are correct-- I did not read "double depth" in your original post. The light came on in my head after I went to bed last night about how you stated the formula. Jim (17215)
So you are adding 15% for the compound movement, got it, thanks. The explanation got a bit confusing. JP (17219)
SD= 0.6495/TPI or SD=Pitch X 0.6495. REMEMBER that this only works if the tool bit used is ground with the proper width of flat on its tip. This can be found with the formula Width of Tip = Pitch x (1/8) for Ex. 16 TPI equals a pitch of 1/16 or 0.0625; thus Width of tip = .0625 x (1/8) = .0078" When the compound is set to 30 degrees your tool bit must travel along a longer path. It is easy to calculate a constant for this. Assuming again an American Standard Thread with Pitch = 1" we can start with our SD of 0.6495". To find our new distance use simple trig. ; We have a known side (0.6495) and a know angle (30 degrees). If we sketch a right triangle our known distance is the side adjacent to our angle and our unknown is the hypotenuse of the triangle. We can use the following formula: cos of angle = adj/hyp ; or hyp = adj/cos of angle thus hyp = 0.6495/cos 30 = 0.750 Again since we used a pitch of 1" to find this we can use this as a constant for finding the amount the COMPOUND must travel for a given number of TPI. Distance = 0.750 / TPI or Distance = 0.750 x Pitch. Ron's constant of 0.5773 is a ratio of of the above calculated constant (.750) to the double depth of an American Standard thread with a pitch = 1". Constant = 0.750/1.299 = .5774 EX. American Standard Thread with 16 tpi. What is SD for Compound parallel?; what distance does compound slide when set at 30 degrees? 1) Compound parallel SD = 0.6495 /tpi = 0.6495 /16 = 0.0406" 2) Compound at 30 degrees Compound Travel = 0.750 / tpi = 0.750 / 16 = 0.0469" or with Ron's formula DD=SD x 2 = (0.6495/16) x 2 = 0.0812" Compound Travel = DD x 0.5774 = 0.0812 x 0.5774 = 0.0469" both work but I like using the first better as DD does not have to be calculated and the constant 0.750 is easy to remember. You can also calculate constants for finding SD when using a sharp V tool for American Standard Threads (i.e. not ground to correct profile with flat tip). If any one is interested just let me know. I apologize for the length of this post, but I really got into this. Russ (17228)
Russ: Excellent explanation!!! You put to paper nicely what I could not. Like I said, I wish you could all come over and we could thread together and you would be surprised at how easy it really is. BTW: In previous post when I said I do most of my threading with cross-slide Parallel with workpiece and feed in with cross-slide I left out one other little tip for those that might like to try threading this way. As you near finishing Single Depth of thread take the compound and move a couple of thous forward so tool only cuts on front side of toolbit and test for fit. If tight then take tool back towards tailstock a couple of thous so tool cuts only on back. Test for fit again. If tight then repeat procedure again after taking another thou or so in on crossfeed depth. This method will also work to help take chatter and or burrs or "rags" out of a thread which you will sometimes get when threading with my method. Ron (17229)
That's all very interesting Russ. However, I feel I should point out that the American Standard Thread Form is archaic. It was replaced many many decades ago by the Unified Thread Standard. There are important differences between the two in regards to thread depth. Ed (17266)
Ed, you're absolutely right. Being an avid collector and reader of older reference material I sometimes find myself using information that is somewhat dated. However, the mathematical concepts remain valid and it was with regards to the math I was writing. An examination of newer thread profile data such as that found in Machinery's Handbook 26th ed. will yield the material necessary to find constants that are "up to date". As far as thread depth goes, it appears that the Unified thread form is slightly shallower. Instead of a constant of 0.6495 being used it might be more appropriate to use 0.5413 found by multiplying 0.86603 by 0.6250 (revised depth compared to a standard V-thread). Other factors such as class of fit, etc. may need to be taken into account. Thread cutting tool profiles would have to be adjusted accordingly as per modern standards. According to Machinery's Handbook, threads cut to the American National Standards that were previously discussed are fully interchangeable with the Unified standards. I apologize for the confusion. Although I'm relatively young, much of the material that I have educated myself with has a lot of years on it. Then again some of my machinery dates from the 19th century, so the two (my library and my machinery) seem two go hand in hand. Russ (17301)
I agree that 0.86603 times the pitch is the depth for a sharp V thread. And I agree that 0.6495 times the pitch is the depth for a American National Thread form. But my text book ("Machine Tool Practices" 4th edition) says 0.6134 not 0.5413 times the pitch for external Unified Thread form depth. That is based on a flat at the top and bottom with a width of 1/8 times the pitch. It gives 0.5413 times the pitch as the depth for an internal Unified thread. So we are close! Ed (17308)
ED, Machinery's Handbook 26th edition in table 1 "American Standard Unified Inch Screw Thread Form Data" lists both internal and external UN thread forms in the same column. It gives thread depth as 0.54127 X pitch for both. So...., I looked the same table up in Machinery's handbook 21st. ed. and here the data is listed separately for internal and external threads. Internal is 0.54127 x pitch and external is 0.61343 x pitch ... the same as you're reference lists. Correspondingly, the illustrations for thread profiles are also slightly different. 21st. ed. uses standards revised in 1974 and the 26th. ed uses standards revised in 1989. As I understand it most of these changes have been made to correct problems with maintaining tolerances in some production activities. Threads manufactured to the newer standards are also suppose to be interchangeable with those made using the older standards. I do not know how true that is, but I've never had any problems with fits when using data from older references. Of course I am not doing production runs either! Russ (17325)
That's interesting Russ. My text book is dated 1991 so it should of had the 1989 standards. I have a copy of the 25th edition of Machinery Handbook (1996) and it also shows a single column with 0.54127 x pitch. Oh well, I guess I'll stick with that. Also, keep in mind that they are *increasing* the minor diameter since they are decreasing the depth from 0.61343 x P to 0.54127 x P. Well... wait a minute. They may have kept the minor diameter the same and decreased the major diameter. Can't tell since I do not have the earlier standard. Perhaps you can tell. Ed (17344)
I am finding out there is a lot I do not know about thread standards! Comparing different texts it looks like they are increasing minor diameter. Reviewing MH 21st.ed. again revealed that the constant 0.6134 appears to have been derived by including an allowance for the optional rounded root. This amounted to 0.08333H, or in our case an addition of 0.07217, being added to the basic constant 0.54127... which is of course equal to 0.61344 The radius is listed as .14434 x pitch. Sides were to be straight beyond the apex of the radius. The width at this point corresponds to 0.25 x pitch, which is the width of the root for the basic profile of the UN thread. It would seem that in order to use the constant 0.6134 a tool bit with proper radius would need to be used. If a tool with a point .25 x pitch were used at thread depths found with this constant, the flanks of the thread would be wider apart at the pitch line than the standard calls for. Also, the resulting flat at the peak of the thread would be narrower than the standard .125 x pitch. In MH 26th ed. the same profile diagrams show some changes. First the radius of the optional rounded root has changed. It is now 0.108 x pitch. The constant used for depth is derived from .625 x H or in our case = 0.5413. No allowance for a rounded root is added "except" for the diagram for the actual UNR thread profile. Even this number has been changed. Using 0.5413 with a tool bit ground with a flat of 0.25 x pitch should give the proper depth and resulting profile. BTW the old standards that were originally discussed used a flat of .125 x pitch for both root and peak. I also noticed that in the thread tables such as Table 4a in MH 26th. ed., the numbers given for minor diameters are based on the UNR form and include the additional depth for the tool radius. I guess what formula or chart you use depends to a great extent on what kind of threading tool you use and what its profile is. I am guessing that older thread tool grinding gauges may not give the correct geometry if using the latest threading data. I just realized we haven't even touched on thread Classes and fits! It might be easier to buy my threaded products at the hardware store! Russ (17360)
Thanks for the information Russ. It is complicated. I use an Aloris tool post with their HSS cutting tool. When it came it had a sharp V on it and I stoned it down until it "looked" right. I'll have to check it. To be "right" I would have to use a different cutting tool with a different width flat for each pitch! I'll just stone it for a mid-range pitch. There is an easy adjustment for the helix angle which I use. Also, I'll use the latest depth specifications as a guide. Usually, like most people, I cut a thread until the part I'm mating to fits properly. Ed (17384)
Correct Thread Depths without Calculation
There is an easy method of getting the depth of cut correct when threading without arcane mathematics. It also gives the correct results when the top slide set-over is not exactly half the thread angle. The lathe does all the maths for you. Here is the method for external threads, 'tis faster to do than to read! 1) Set the top slide over to half the thread angle (ie 30 degrees for American threads) or about a degree less which will give a cleaner result especially on difficult materials like phosphor bronze. 2) Set the tool correctly relative to the work in the usual way. 3) Wind the top slide in or out to a convenient part of its travel. 4) Use the cross slide to bring the tool point almost up to the work piece and feed the top slide until it touches being careful to ensure that all the backlash has been worked out. 5) Set the cross slide dial index to zero. 6) Set the top slide dial index to zero. 7) Move the saddle so that the tool is clear of the work. 8) Feed in the cross slide to the correct thread depth as given in your preferred reference book (most of us Brits seem to use a thing called the Zeus book). 9) Set the cross slide dial index back to zero. 10) Wind the top slide back to clear the work and move the saddle up to the thread cutting starting point. 11) Move the top slide in and take the first cut. 12) At the end of the cut withdraw the tool using the cross slide and take the saddle back to the starting point. 13) Return the cross slide to the zero setting. 14) Put the feed for the next cut on the top slide. 15) Make cut and repeat procedure until the top slide dial reads zero. Result one thread cut to the correct depth as set by the cross slide feed in step 8 an no mathematical head aches. Its a lot easier if you have the proper South Bend thread cutting stop because that provides a positive stop for the cross slide in feed prior to each cut, you don't have to move to a carefully read dial zero setting. If you set the cross slide over to slightly less than the thread half angle a tiny shaving cut will be taken by the trailing flank of the tool. The chips coming off the stock can score the trailing flank, tough materials like phosphor bronze can be a particular problem, leaving a sporadically rough finish to the thread. The trailing edge shave removes this. Thanks are due to the late Eric Hopekirk for teaching me this and to Geo. H. Thomas for explaining WTHIGO. Clive (17230)
Clive, I really like your method. I'm going to try it ASAP. I still like knowing how to calculate Single Depths, etc. as I do not always have a chart or handbook with me. BTW your technique is obviously valid whether you get your thread depth from a book or from an "arcane" mathematical formula. Russ (17231)
Clive, Your post and Russ's post are what I like about this site. I've worked in a machine job shop for 22 years and I've not heard of this method. Sounds so easy, I've got to try it. Thanks to both of you. Jim (17232)
Jim, Clive, Russ et al, I have followed this thread with interest and I have used the mathless kink myself for some years. i was a little surprised that no one related the 0.5773 coefficient to tan 30 deg or 0.5/0.866. it is helpful to know and understand the math while using the mathless method. using the math can get you in trouble if a digit falls thru the cracks un-noticed while understanding both methods helps to notice the un-noticed. another useful formula is that for the thread helix angle which is the arctan (pitch/circumference). For example: the helix angle of a 1 1/2" x 8 thread would be the angle whose tangent is 0.125/(1.5*pi) or 0.27. this angle should be added to the relief of the forward cutting edge of the tool bit while a slight relief on the trailing edge will enable the 30 degree setting of the compound to effect a much cleaner cut. It should go without saying that the cutting edges should be finely honed also. If I have muddied the waters that others have worked to clear, I apologize.  joe (17235)
Joe, By using the tan of the angle you are controlling the width of the thread rather than the depth of cut, correct? JP (17236)
No one has mentioned the problem I had with my first thread. Started on a piece of scrap to cut some 1/2 X 20 threads. When I was done I had created what I kept around for a few years calling it my "Universal thread sample" I don't think I could find any nut in the shop that somewhere along that shaft that the nut would not fit. This was because no where in the detailed instructions I had read up about cutting threads no one had told me "NEVER DISENGAGE THE TUMBLER GEARS! (17244)
JP, the width of thread and depth of cut is the same if feeding with the compound and my reference was to Ron's response which I paste here to refresh memories. Degrees is Double Depth X .57773 which will be a larger # than Single Depth. thus the feed on the compound is 2*tan(1/2 thread angle)*SD. this is the amount you will have fed the compound in if you backed off the cross-slide an amount equal to the SD in Clive's method. Arcane math a scientific calculator can be very handy if you don't have Clive's favorite book handy or your own fave book or Ron's now generously posted spreadsheet. i love spreadsheets but hate Microsoft so will have to generate my own in quattro pro. joe (17256)
I think I will stay with .75/tpi JP (17259)
Clive I made some 1-1/2 6 thd. x 15" bolts for a customer Friday and tried your method. Works slick. Jim (17284)
More Threading - Tapered Pipe Threads
I'm looking to build an improved stand for my new (yet to arrive) 4x6 bandsaw that I've bought off E-bay. I'm looking at George Carlson's web page http://www.homemetalshopclub.org/projects/sawstand/sawstand.html and am looking to build something similar. I'm going to try to build the coolant nozzle as shown in the plans http://www.homemetalshopclub.org/projects/sawstand/sawstand.pdf  and am going over the process for cutting the 1/4" pipe thread mentioned in the Machinery Handbook (thanks John!). I'd like to go over what I understand will be the process. My taper attachment will be set for .75" per foot. I'll turn the scrap brass I have down to .540" (for the threaded portion as the upper portion of the nozzle will be .5625"). I'll set the qc gears to 18 tpi. and the threading tool will be 60 degrees set square to the pipe verses to the taper. The maximum depth of thread will be .04444". I plan to use aluminum instead of brass as I have a pretty good selection of aluminum and a very small supply of brass. The total length of threads will be about .5946". Does this all sound right, or am I mistaken/missing something? Dave (17290)
I've already found a mistake with my plan. The narrow end of the nozzle will be .500" and the large end .5946". So I guess I'll have to turn the large end down to .540" for the threads. Dave (17292)
David, Unless you are really determined to cut pipe threads, then I'd just use a tap and die. You can straight thread the parts to the pipe threads maximum diameter and then chase the taper form of the threads with the die or tap. Now if you are determined to cut pipe threads on the lathe, make sure you have a fairly positive way of returning the carriage to zero at a certain point. I would use dial indicators. And remember to turn the dial in (or out) to take up slack depending on ID or OD threads. Tom (17309)
Threading Primer anyone?
I've been cutting threads now for a little while, and I've picked up some really invaluable and time saving tips on this group; thanks, all... short of standing next to one of you old timers and watching, I don't know of a more versatile resource. Question: last night I was working with some rather hard stainless (700 series) and some really hard high carbon steel. Threading both of these yielded the same mediocre results: I can't seem to get a good cut when incrementally feeding the compound (29 degrees for external threading) in at a thousandth at a time. After a cut, I have to advance it about 5 thousands at a time or nothing happens... if advanced one or two thousands, the bit slides into the old cut and no chips peel off... after about 4 passes of this (one thousandth at a time), then it will take one rather heavy cut; the chip that comes off is not the shiny, thin ribbon I like to see but a rather thick, flat color that cracks and twists and breaks without pattern. I suspected looseness in the setup so checked everything I could but it appears to be fine, no play that I could detect; mic'd the height of the cutting bit and it's fine as well, vert height is within a thousand or two of actual center of turning piece. I am beginning to suspect the carbide bit is dull, will change it tonight to see; any other suggestions? Or is this just a fact of life with hard materials? (17633)
You have two things working against you in this setup. Carbide tools are difficult to thread with on an engine lathe because they require great rigidity and adequate speed to "work" the carbide. Threading with carbide works better on a large industrial CNC where sufficient speed and rigidity are present. I only use high speed steel thread tools on a small engine lathe. The materials you are using are very demanding, especially the stainless steel. Stainless tends to work harden. Light cuts on stainless tend to rub on the surface rather than penetrating smoothly. This rubbing results in work hardening which is similar to hardening due to heat treatment. When you feed deeper, you break below the hardened surface, but you are probably incurring large forces on the tool and lathe. You might try a high speed thread tool run very slowly and use a good cutting oil. (17637)
Thanks for the tips, Tinman and Ron. I checked with Enco and they don't seem to have any HSS bits pre-ground to 60 deg. I could grind down my HSS cutoff tool and use that, but I'm afraid that all my bits are carbide since they seem to last longer than HSS in the (mostly) difficult stuff I like to cut. I used to remember seeing a 'snail' looking tool that was already ground to 60deg included, and all you had to do was grind off a bit of the top of the helix and you'd have a sharp threading tool. Who carries these now? (17649)
Kaipo The threading problem you describe convinces me that your tool is just a hair above the centerline. Try lowering it just .010" and see what happens. If it improves, try lowering it again. You don't say what typical diameter you're trying to thread, but that's relevant, too. I thread stainless and lots of Rc35 stuff with carbide tools every day with no problem. Do not make a threading tool out of a parting tool. Too flexible in the left-right direction, and the clearance on the bottom must slope to accommodate the spiral of the threads, which will be hard to do on the parting tool. Grind adequate back clearance on the tool. Often, folks grind carbides with almost no back clearance. A green wheel is just fine to sharpen carbides. Buy a 1/2" wide green wheel. Wider is of no use for sharpening bits and costs more. Somebody asked what maximum horsepower can be safely used on a 10". You can put 20 HP on if you want, but you're only going to get what the belt can deliver, to the spindle. One HP (single phase) should meet all your needs on a big 10. (3/4 HP 3 phase is more than enough). When the belt slips, that's your limit, not the motor size. Like big motors in cars, it all comes down to what you can deliver where the rubber meets the road. Harold (17662)
Threading question
Is there a listing somewhere of the standard size and pitch for threads used in optical mounts? JP (18134)
JP, What kind of optical mounts are you talking about? Fred (18136)
The threaded lens holders with the threaded retaining rings. JP (18141)
What diameter lenses are you talking about? Frank (18144)
To mount lenses or mirrors into and to mount an lens assembly to a system like an objective lens assembly to a stero microscope base. I have a Bauch and Lomb stero zoom 4 with no objective lens for 1 and I am tinkering around with building a spectroscope using a spherical mirror in the collimator etc. So keeping things standard and knowing what to order would be good. JP (18149)
If you are talking about the thread for supplementary lens for the B L stereozoom, I recently made an adapter for the StereoZoom 7 which was 38mm x 1.0mm pitch. Ted (18151)
Would this be the single lens that comes in 1x, etc? IF so, would you have anymore of these or know where to get one? (18154)
Measure the threads on the B L nosepiece that is missing the objective. You will need to mount your new objective lens in a cell that can be threaded into the B L nosepiece. With mirrors it also depends uppon the size. With larger mirrors one rarely uses threaded cells. Frank (18155)
I have an AO and an Olympus stereo microscopes and the lenses for them are quite cheap if you find a second-hand microscope or lab supply dealer. Objectives that cost thousands of dollars (for example a high NA Zeiss 40X dry is really quite cheap in the second-hand market. Frank (18157)
JP, I have the following from Nikon lens specification guide. 52mm is 0.75mm pitch 72mm is 0.75mm 86mm is 1.0mm 122mm is 1.0mm These are industry standards for filters, retaining rings and lens hoods. I only have published specs for the above filter sizes. Somewhere between 72 and 86mm the pitch obviously changes from 0.75 to 1.0. Ted (18158)
I'm speaking of the one/single 1x or 2x large lens that goes over the objective lenses. It's about 40mm in diameter and fits a BandL stereoscope. (18159)
In the case of the StereoZoom that I am familiar with, you should have two objective lenses which are mounted up inside the nosepiece and the nosepiece is internally threaded as 38mm x 1.0mm pitch. I could not find any adapters or lenses of that type so I made an adapter from a piece of pvc pipe that I threaded as 38mm x 1.0 epoxy glued it to a 52mm camera lens stepup adapter. This arrangement allows me to use 52mm filters, polarizers, and supplementary lenses like 2 to 10 diopters. This is a very handy adapter for the StereoZoom and B L used to sell supplementary 2x to 5x lenses that attached to the 38mm threaded nosepiece. Ted (18160)
Very neat solution! The stereozoom is a nice microscope and that is certainly a slick attachment! Frank (18163)
Thanks for all of the info, I think I will build the adapter. JP (18175)
Depending on the size of the optics, barrel mount or shutter in which the optics are mounted the sizes mostly(in my experience) range from .50 mm for rear mount and also on front mount threads on smaller optics to .75mm, and 1.00mm for many lens retaining rings, front mounts filter rings and up to 1.50 mm for lenses usually larger than 75 to 100mm or larger diameter. These thread sizes have nothing to do with focal length just the diameter of the optics. I have never seen threads other than metric used on lenses, even US lenses like Kodak's ektars. There may be others used but I'm not aware of any. Curiously, the threads for mounting cameras to tripods etc. has been universally standardized to be 1/4-20 for most cameras and 3/8-16 for larger cameras. 3/8-16 was used on many older cameras but 1/4-20 seems to now be used more. (18196)
First Threads
I just had to send this in to the group for a laugh if nothing else. I finally was feeling well enough and brave enough to try threading on my old Heavy Ten. I re-read the letters that were flying around several weeks back and gave it a whirl. Well the first try was a 3/4x10 in steel. I set the compound at the suggested 29* and tried to zero things up on the calibration rings. First problem, my compound slide ring wouldn't stop turning as I turned the handle. I discovered it was missing some type of washer between it and the compound. I made up one out of some HMW plastic and solved that problem ok. It works very smooth now. I started to cut the thread and found it looked very odd. I kept at it for a while but things just got stranger. I took a break and thought it thru again. I found I had dialed in 59* in relation to the work instead of the required 29* .It's an easy newbie error due to the way my compound is marked, it really is trust me Anyway after that I tried another thread operation this time with 1/2x13(metal was getting smaller). This time things went very nicely and I'm feeling way better:-).It was rather easy really and I no longer feel nervous about threading at all. Oh, one other thing. In the discussions everyone reached a formula to find depth of cut for the final setting of the compound and I followed the directions to the letter. It turned out to be only 1/2 the final depth of cut on my lathe so I had to double the input on my compound slide. Not a big deal but it did confuse me for a while, not hard to do anymore for me since I got sick. I finally thought it all out and am confident with doing any size external thread. Had a lot of fun for three hours and am keeping the finished product for posterity. Now about those INTERNAL threads. Hope I didn't bore everyone but this is a rank newbie's type of adventure and you pros probably forgot what it was like the first time round . BTW thanks for all the help, I couldn't have done in even three hours without the folks here in the group. Tom (18641)
Opps, That should read, my calibration ring wouldn't turn at all when the slack was taken up turning the handle inward, obviously missing some kind of washer. I can't even write about these things properly let alone doing them on my lathe. It does get annoying though, I wasn't always like this folks I also forgot to say this hobby is very "therapeutic" and a great for me Keeps the mind running. Tom (18642)
Congratulations Tom!! Now try the method in message 17230. For the thread depth use the chart on your thread gauge or as some call it, the 'fishtail' gauge. The list of numbers is the double depth of thread so use half of the listed number. This way you won't need a book or calculator or spreadsheet. Do it once or twice and you will never forget the method. When you are ready let me know, I have a need for a few special bolts g JP (18667)
Thanks JP that is the message I have in my saved massages(#17230) it worked great and became intuitive after using the method. I still will have to try an internal thread and it seems to be a bit different g another week or so to get up the nerve and figure that one out g fishtail gauge doesn't have any depth of cut markings or numbers, must be a cheapo. Tom (18678)
Tom, I've copied the Double Depth Of Cut from my center gage. I'm going to cut and paste/print and post next to my lathe. The numbers on the gage are so small, and my eyes aren't what they used to be... Dave TPI - Double Depth Of Cut 3.5 - .371" 4 - .325" 4.5 - .289" 5 - .260" 6 - .217" 7 - .186" 8 - .162" 9 - .144" 10 - .130" 11 - .118" 12 - .108" 13 - .100" 14 - .093" 16 - .081" 18 - .072" 20 - .065" 24 - .054" 28 - .046" (18681)
Threads on a long rod (14 feet)?
I need to put threads on the ends of 9/16 dia round stock 14 feet long. One end needs only about 1" threaded the other end should have 2 or three inch thread. I'm looking for advise on how to put the threads on. I have a 9 inch model A but I'm unsure about how successful it will be to build a couple of supports for the almost 14feet of rod sticking out of the lathe? What depth of cut do you use when threading steel - I get an OK finish when I take .005/pass but it's really lousy at .010 or above, and at .005 it will take quite a few passes to get a full thread (threading can be course or fine). Has anyone ever done this? Is it better to cut the threads on the lathe with a bit or get the appropriate die from McMaster? Any other options? I know I could have a threaded section welded on or make a collar which would be pinned to the rod on one end and threaded on the other. But I think these would be more trouble and cost more. The purpose of these rods is to replace the collar ties on a workshop/garage/barn I had built. Paul (21526)
A buddy did almost exactly this. He used one or two supports that he made up that were a couple bearings side by side so that the rod sat in the middle (and had a screw height adjuster). Worked fine, no drama at all. Mark (21529)
Cutting that on a lathe would probably be more trouble than its worth. I would weld a threaded section or a bolt to the end of the rod. Second thought is to weld a short piece of angle iron to the end of the rod and drill a hole in the perpendicular flange. Second option would be to use a die and thread it by hand. Third option is to make a long holder out of a piece of 1/2 in schedule 40 pipe. The ID is a little bigger than 9/16". This would probably be more trouble than both of the first two options combined. If you really want the easy way out, use a piece of chain and a turnbuckle. JP (21531)
I would simply thread them by hand using a die, stock and cutting oil. No machine required. Ted (21533)
Paul, I am not sure of the quality of threads you need. Threading on a machine, usually you can take .020 on the first pass then .010 on the next two. Then .005 till you need to finish the threads up. The .001 for a few passes. I have usually found when threading with a die, the larger the thread the worst the quality. 1/2 is usually the dividing point. Other may have different experiences. If you need good threads on the 9/16 rod, I'd get an adjustable die. Cut the threads oversized initially. Then adjust the die to proper size for finishing. Beaver use to make (and may still) a power threader for pipe threads etc. I used one a couple of times. Real nice, cut good threads and had replaceable threading dies. Still, 9/16 threads should be OK to do manually. Use a new die. An old die might have been part of the problem with some of the threading I did. You could even do it on your lathe, to start the threads square. Just put in the stock thru the headstock. Use the tailstock to put pressure on the die into the workpiece. IE the quill pushed the die/die holder into the rod. Turn the chuck with the chuck key. Don't need as much supports for the stock as you are not turning under power. Still some would help or even a table to rest the rod(s) on. Tom (21535)
This tends to add to the difficulty of getting a good thread. If your using CRS the only problem may be hard spots in the metal. A die is much easier, if you can use a standard thread. I would think a bit on whether a collar tie even needs threads there a turnbuckle or something that requires a thread be provided. RC (21536)
My thoughts exactly. You could thread both ends by the time the lathe set up is ready to do one end :D BTW What was/is wrong with the original collar ties??? They usually last the life of the house - (at least the timber ones we use in Western Australia do) -- Peter  (21537)
I also would think that using a die would be the best solution but some means must be provided to keep the thread straight or centered. I have been surprised at how much a die will drift off center if not guided. Perhaps you can come up with some piece of counter bored tube that would hold the die square and guide on the rod. marty (21540)
Paul, If you want to thread in the lathe, the supports do NOT have to be very sophisticated - a 2X4 with a hole in it clamped to anything to hold it upright will work like a charm. (21541)
Paul- you will probably want to chuck up the piece and turn the threaded end down to the right OD for your dies. that way, it will cut nice and clean. I can not remember what the percentage is, but you should be able to look it up in a machinist's handbook. put up a simple support on the outboard end. does not have to be perfect or perfectly inline. a 9/16 hole in a 2x and some grease clamped to some kind of support. you may want one in the middle too. use the lathe and backgears to drive the stock into the die. are you using a turnbuckle? then you will want LH threads on there too. (21542)
Threading your bar stock
Some jobs require a sense of humor just reading the directions! I like the JP mind-set, "What do you really need to happen?" If it can work quick and dirty, but still have strength, weld that sucker. No welder? no problem! Use the die-stock idea. Look, all we need here are some wrinkles that won't fail when your mother-in-law visits. Nobody wants a shingle to land in her new 'do! The problem is alignment of the die. Go get a 2-piece die the right size with die-stock to match, (these are adjustable). Now either find a thick-wall pipe or make a seating gage. All this has to be is a bushing with a large flange on one end. The tube hole just has to be a slip-fit. Take a side-grinder to the end of your rod, (OK quit wincing guys!) while a friend turns it. You now have prepped the tie-rod. Slip the bush over the end of the rod and hold it up to the dies-stock. Actually your partner can hold the bush while you press against it, (I'm gonna get banned for this one!) As you turn the stock, feeding on to the rod, keep it tight on the bush. All your doing is to keep the die square to your rod. Once the dies have some thread behind them, the bush can be discarded. Do NOT use your lathe for this work. This is first-class shade tree engineering. A stump and some pipe wrenches should hold your rod while you work on it. Fourteen feet huh? This is about as basic as it gets. And it'll work. Which just goes to show that there are times when a half fast bush is better then welding your other foot to the floor. Keep the cooler well-stocked...with cutting oil of course! This message was approved by my wife who is NOT running for anything, but is getting out of ground zero! Ron (21543)
Sound like the medication just kicked in, but I like this answer. JP (21544)
Ron that is the best laugh I have had in a long time keep up the good writing. I take my hat off to you! Thomas (21554)
110% well said! Collar ties are not precision fasteners :D I especially like the bit about the side grinder :D We call them angle grinders here in Oz. Peter (21555)
Since some people seemed to want to know why I am replacing collar ties... The shop/garage area is 24 x 36 2 stories. for finishing the second floor the collar ties break up the roof line - almost forcing putting in a ceiling at the ties. What I want is the visuals of a cathedral ceiling. 9/16 steel rods will not visually break up the space like 2x10's. Yes I also know that if I had realized this when I had the building built I could have constructed it so collar ties were unnecessary. As for threading them I know I don't need a precision fit and as long as things are not to short you can take up extra space with spacers. Also need a real threading die not a rethreading die. On turnbuckles - I originally wanted to use wire rope. But the local building inspector insisted on solid steel rod so that is what I am stuck with. I got stock long enough so I don't need turnbuckles in the middle and that minimizes the number of fasteners I need to attach. Paul (21586)
Newbie trying to thread on a heavy 10
I've tried my hand at threading on my 10L without a thread dial. As a newbie I haven't a clue how to start but was able to produce a 3/16 by 32 tpi screw with a nice knurled head for the compound feed dial. I started by turning a bolt to .187 and the final diameter was .157 so I lost about .020 in the process. Next I tries leaving the diameter heavy about .207 and threaded until I reached the final diameter. The trick is starting at the same point on each pass. Any suggestions how to achieve that? I set the cross feed to zero at the end of the pass, back off one turn, return the carriage to the start position and bring the tool back to zero on the cross feed, then turn the compound for the next depth of cut. I keep micing the diameter to try not to cut it too small. I tried turning both between centers and from the free end of a collet. (22032)
As long as you use thread pitches that are an even multiple of the lead screw pitch (8, 16, 24, 32, 40, TPI etc) the thread dial is not needed. Also, the half nuts can be disengaged and engaged to retract and start and new cut. To begin, set both feed dials to zero on the stock surface. Use the top slide (compound) for setting the cut amount only. At the end of the cut retract the crossfeed only and disengage the nuts. Return to the start (off the stock), set the crossfeed to zero again, set in more cut on the compound and close the nuts. The motor is always running. All this happens faster than you can read about it. Thread at dead slow speed in back gear until you get used to it. Stopping the cut is a matter of opening the nuts and the crossfeed instantly at the correct place. Also, a stopping groove cut at the end of the thread cut to thread depth will allow you to stop by disengaging the nuts without retracting at the same time. RichD (22045)
If you are only doing short threads seriously consider making up a handle and turning the lathe spindle by hand. Up to say 20 ish turns its effectively as quick, for the non-expert, as power feed, especially when you have no dial. Advantage is that you are totally in control instead of chasing the lathe. You can stop the cut exactly where you want each time and use hard stops clamped to the bed without risking a smash up. You also get to feel exactly what is going on, a great help when you are just starting. Under power a slightly mis-set or inadequately sharp tool will just be ploughed through the work leaving you wondering why the job is rough. By hand you can easily feel the difference a "just right" tool makes. I used to do virtually all my threading by hand on the S-B 9". Making a mandrel handle for the Heavy 10 has been on my Round-tuit list for ages, just need to do an expander to fit the back end of the bore. Keeping track of cuts can be a problem. My personal preference is the top slide angular in-feed method 'cos you do all the thinking and setting before you start the job. (Hopefully I'm not the only one around here whose normal metal state during screw cutting is only a few thou on the controlled side of panic) Just need to remember that the job is finished when both dials get back to zero. I think the step by step instructions are in the FAQ section. (22062)
480 TPI
I have a very good friend who has worked w/ a lot of lathes over the years and he has said that he has never seen this. There is a G pin hole on the quick change gear box and the TPI plate goes up to 480 tpi. Has anybody ever seen this on a Heavy 10 . Vinnie (22590)
Mine also has the 48 tpi setting. (22591)
Verne: First thanks for the quick response. Secondly do you know what these lathes were made for. I don't think that they were used for threading as where would one use such a thread cut. Also how uncommon are they. Vinnie (22593)
The dual tumbler gear box goes to that. I had asked on this list some time back if anyone attempted this fine of a thread. What I got back was 120 tpi was the finest matching thread someone here has made, at least with the people who answered then. Let us know how your 480 tpi nut and bolt turn out g (22596)
The lathes were made for tool rooms and schools. They give you a very fine feed when your are doing crosslide work. (22601)
The wide range gear box on the tool room heavy ten I guess they call it is very useful in some trades. I think the 480 is a joke part for some, myself included but the fine turning is ok. What we find useful is something most dont notice, below there, it cuts like 27 tpi and 30 tpi. Very useful in our line of work, I started refusing to buy lathes that did not have the box years ago because Winchester and some others like to put 30 on some of there guns we work on. Also a plus, is the more variety they offer makes cheating to get some of the metric threads done easier. Grumpy (22607)
Grumpy makes a good point about the wide range gear box. Also, I believe that the wide range gear box doesn't require changing the stud gear to get the courser pitch threads like the standard gear box does (another plus). Both standard and wide range gear boxes were available in double tumbler configurations. I have only seen single tumbler gear boxes in standard range configuration. Webb (22609)
Vinnie writes: I have a very good friend who has worked w/ a lot of lathes over the years and he has said that he has never seen this. There is a G pin hole on the quick change gear box and the TPI plate goes up to 480 tpi. Has anybody ever seen this on a Heavy 10. I see there have been several responses to your question with some useful information. It might be interesting to look at the historical development of the QC gearboxes applied to SB lathes. The following is to the best of my knowledge. Earliest version is what is now known as the single lever gearbox. What this actually means is there is one tumbler selector at the bottom of the gearbox which can select between 8 different gear ratios for fine division choice of pitch. On this gearbox there is an additional lever at the top of the box which controls a sliding gear inside the box to select between 3 range ratios. As 24 ratios in 3 ranges was considered insufficient they added a sliding gear mechanism in the change gear train to select between high and low "super-range". So now you have 8 ratios times 3 ranges times 2 super-ranges giving a total of 48 pitches covering 4 TPI thru 224 TPI and also 48 related longitudinal feeds and 48 related cross feeds. (The feeds are not identical to the threads because there is additional gearing inside the apron which results in additional reduction.) Probably for convenience of operation, they decided to get rid of the sliding gear in the change gear train and expand the number of ranges selectable directly at the front of the gearbox. This required a complete redesign of the gearbox. They deleted the sliding gear selected by the top lever and added a whole new section at the left end of the gearbox to select between 5 ranges. For some reason they decided at that time that having more than 5 ranges directly selectable wasn't practical but they didn't like giving up the other 8 pitches so they allowed the option of changing to a larger stud gear for the coarsest pitches. So now you still have 48 pitches, 40 directly selectable plus 8 available by changing the stud gear. And, of course, you also have the 48 longitudinal and 48 cross feeds. Some people were unhappy with the fine feeds not being fine enough. Some were unhappy with having to change the stud gear for coarse pitches (and having to change it back for the more usual requirements). And some thought the fine pitch selection was inadequate, specifically the lack of 27 TPI, and the lack of 30 TPI and its multiples. So the redesigned the gearbox again. This was actually a less radical change than the change from single lever to two lever 48 pitch. The new design expanded the right end of the previous box to add to selections on the cone, and expanded the left end to add two additional ranges, one coarser to eliminate the need for changing the stud gear, and one finer to extend the fine feeds to an even finer pitch. (For reasons of gear train geometry it happens to be convenient to add two ranges at a time. By adjusting other details of the change gear train the additional ranges can be coarser or finer. In this case they expanded the ranges at both ends of the scale.) This gearbox gives 10 ratios directly selectable by the right lever time 7 ranges directly selectable with the left lever for a total of 70 pitches from 4 TPI thru 480 TPI. And, of course, it gives 70 longitudinal and 70 cross feeds. This has hardly been an exhaustive dissertation but I thought some of the members might be interested in how we got from "there" to "here". Anthony (22614)
Threading with tailstock die holder
Could someone tell me where to find the step by step procedure for using a tailstock die holder for threading? It seems that it would be pretty simple, yet I've tried a few times and end up with no thread at all. So I need to know what I'm doing wrong. Joe (22834)
A small chamfer on your stock might help. (22836)
I haven't had a problem with mine. First I assume you have the correct side of the die facing the work? The as below a small chamfer will help. I don't have my tailstock bolted down when I do the next step. Just snug enough so the tailstock will still slide on the ways. There is quite a bit of force on the tailstock when using a die. I just push the just barely loose tailstock against the work and the die will begin to cut and feed on its own. I do this in the lowest speed possible - no hurry here. Have your other hand on the switch to shut off the lathe when you reach the depth of your cut or something goes wrong. Shut it off, let the spindle stop then switch into reverse to back out the die. Don't forget the oil! Alex (22837)
Joe, I had this problem once. Bad die. Thread the die only onto a long screw. Check the die for squareness with the screw. A die holder will force the die faces to stay square regardless of the actual die thread angle causing it to strip the thread. RichD(22838)
No Take a test part and cut the OD as needed for the thread, then cut an OD of the minor diameter for at least 2 threads, and then cut a diameter midway between. Put a catch pan for the cutting oil under the part and oil vigorously. on pipe cutting machines, they will have a pump that flood oils the cutter. Loosen the tailstock and with hand pressure push it into the metal and start feeding as soon as you get contact. just light enough to allow the tailstock to remain stationary. The first OD will align, the second will allow a bite and the major diameter of the threads will get your threads cut properly. If your throat is not deep enough, just make a small mid OD section. My guess would be that you are locking the tailstock and not letting it ride freely ? Dave (22844)
Joe, I've learned when using a die holder or tapping from the tailstock it is not done under power. The tailstock is locked to the bed and the chuck is turned by hand while maintaining pressure on the die/tap while turning the tailstock spindle handwheel. You can use your chuck wrench for extra leverage while turning the chuck. Russ (22845)
To be clear, I just feed the entire tailstock assembly and not use the hand wheel. I'll go give that a try. Joe (22851)
I agree with a lot of the info the guys have given you. However, you can do yourself a huge favor by converting your tailstock to a lever operated one. It will make drilling holes much easier and threading with tap or die a dream. Not to mention it is a nice project and not too difficult. Bruce (22856)
Great idea. I have wanted to do a quick lock mod to mine. The lever action would also act as it the tailstock was not locked. That free movement is to me at least, the most important part about threading on the lathe. The tap guides for drill presses use a sleeve to hold the tap on axis, but also use a spring to allow the threads to determine where the cutter will move. Dave (22857)
I find that while cutting threads (tap or die) the cutter needs to float. with the hand wheel being cranked and the tailstock not locked, that just makes the cutter movement easier. once the a few full threads are cut, the threads take over and you are not required to feed, but I do anyway. On some harder materials, I will lock the tailstock and crank the feed until I see/feel the threads cutting. then release the tailstock lock. That allows any momentary pause to not mess up the threads. Dave (22858)
Best way to use a thread die on a lathe is to use a tailstock die holder using a hand held (hand held to keep from rotating only) die holder which slides on a straight shank mounted in the tailstock. With your lathe in back gear and at the slowest speed you push the die on the stock (with a tapered end for easy starting) When you reach the appropriate thread length you just release your grip on the die holder and it rotates with the spindle. Then, at your leisure, you reverse the spindle rotation and the die backs off as you again hold the die holder with your hand. Plans for making are in "The Shop Wisdom of Frank McLean'" by The Village Press, publishers of Home Shop Machinist, p. 122, and the same article is also in "Machinists Workshop," Oct/Nov 2000, p.46. A similar die/tap holder, by Michael F. Hoff, Jr. is in Home Shop Machinists "Projects Three," p. 52. Because it is in Projects Three would indicate the article was in one of the early issues of Home Shop Machinists but, I don't know which one. I made a unit like Mr. Hoff's, making a tap holder which utilizes the hardened tap collets from my Hand Tapper (comes with nine collets for small taps) to grip the tap on the shank square. I now easily tap small, up to 3/8 threads on my lathe and using a die, easily thread up to 3/8 or so with this hand held arrangement. As Frank McLean says in the first sentence of his construction article, "A tailstock die holder should be among the first accessories amateur makes for his lathe, since threading with a hand-held die stock is seldom satisfactory." I couldn't agree more. Neil Butterfield Threading with tailstock die holder. (22860)
Cutting 27 tpi?
Tim: The stud gear is your 20 tooth. Change the 56 gear box gear with a 42. Use your 80 that is on the machine. Lever on QC box should be C- 2 I hope this helps. David (23157)
What David says is correct. But I always wondered why one couldn't replace the 56T gear on the input to the gearbox with a 54T gear and set the gear box for 28tpi? If my math is correct, (54T / 56T x 28tpi = 27tpi) this should work also. Any comments? (23158)
According to my spread sheet you can find on the South Bend Lathe Pix file group, your set up will work as well. If you wanted to cut 53 TPI, you would just need a 53T gear, replace the 56T gear with the 5T gear and setup the gear box to 56 TPI. As 54 is a multiple of 27, setting up the gear box to 28 will produce 27 TPI. Guy (23161)
The spread sheet by Guy also does the following. Use your 20 tooth stud gear. Then remove the 80 tooth and use a compound 54/18 to your 56 on the gear box. Put QC lever at A-2 for 27 TPI. I found on e- bay a 54/18 and 72/18 gear for $15.00 each. I have never seen a 42 for sale but one new will run over $100.00. Guy has done a great service to all with his spread sheet. Dave (23165)
Thread pick-up troubles
I have a SB heavy 10 and have been having screw cutting problems. Using the same mark on the indicator it seems to randomly pick up at a different point on the lead screw, so instead of a nice progressive cut it looks as if its trying to cut a new thread at full depth... There are two marks, 2 4, that seem to be the main problem. I've had the lathe for a couple of years now and have noticed it as an oddity before, but I'm doing a lot more screw cutting now and it's becoming a real nuisance. I haven't stripped the apron down so I don't know the state of the pick up gear or half nuts. Suggestions/possible cure? Bernard (24113)
Are you using the half nuts and not the clutch? Are you cutting an "even" thread pitch? If you are cutting a fractional pitch (7-1/3 TPI) or a metric pitch that might explain the problem. Scott S. Logan (24114)
Steve, I respond to your queries below. Yes I'm using the half nuts. The thread that just got screwed, pun intended, was 26 TPI, too much trouble to try and cut metric threads on an inch leadscrew for me. (24117)
Is the thread dial missing any teeth or slipping somehow? (24118)
The gear on the bottom of the indicator is held in place with a set screw. It could be loose. (24119)
I took the TDI off and examined it, the teeth are are bit worn but they're all there. The bottom half of the teeth don't engage at all so it would be possible to machine off the worn portions, I guess? I gear wheel is held by a grub screw and that's tight, no play between the dial and gear. Bernard (24121)
Have had a similar problem. I put a dial indicator (magnetic) on the tailstock end of the ways and move the cross slide back, always, to the same spot, far enough away from the thread to remove all the backlash in the lead screw and cross feed. But always the same spot, Then use the same mark on the thread indicator. This seemed to eliminate the problem. Jim B. (24122)
Interesting. Not quite as bad as the full reversal method and it gets the job done. Bernard (24135)
It might be time to look inside the apron and clean out the half nuts and insure that they are tight in their mounts. I had to use a pick to clean out the half nuts on my lathe when I got it. Oil oxidizes over the years and builds up a hard shellac that has to be scraped out. Also clean out the thread on the lead screw with kerosene soaked masons twine, use a sawing motion with the screw turning. When cutting a thread, make sure that the TDI gear is held snugly against the lead screw and start at the same number each pass, it may help. JP (24136)
Following JP's advice I cleaned the leadscrew with a cord and kerosene, amazing what came out of there, in checking L/S engagement afterwards the big noticeable difference is while the pick-up engages more smoothly the disengage is much more difficult. I guess I'll just have to bite the bullet and strip down the apron and clean the half-nuts.. sigh JP (24219)
Bernie, Pick up some 1.8" felt rope F1, you may need it when you open the apron up. Its cheap and there is no sense in opening it up twice. The upper oiler on the right pass oil into the half nuts and you can externally oil the screw with way oil. This may help some until you get the half nuts cleaned and adjusted. The apron takes spindle oil in the well. JP (24223)
Internal Threading Bars
Does anyone have a source for a good RH internal threading bar? Or plans to make one? Kevin(24235)
I made a threading - boring bar from 1/2" x 1 CR flat bar. I used it in my lantern tool post until I made a tool block. I just drilled the flat bar to keep to top of a 1/4" HSS bit on the center line. Grind the bit to suit. My bit is double ended 60 deg threading on one end and boring on the other. Not pretty but FREE. There are more pics in my SB10K group. Link at the page bottom or click my profile. Bob (24236)
Boy, can this be a can of worms. I say this after having purchased a whole bunch of different sized internal threading bars with matching carbide inserts, spending a zillion dollars doing so. You have to purchase a whole bunch because the ones small enough to cut a 1/4" dia. thread won't go deep enough to cut a decent length 1/2 " thread, and the ones long enough to cut a decent length of 1/2 thread can't thread anything really coarse, and so on. (There's a reason why they make all those different sized inserts) Then you find that to use carbide inserts, you REALLY have to have the machine running fast (just like everyone told you but you never really believed) because you get really lousy threads if you don't; the tool tears instead of cuts. If it at all works for you (micro-diameter being the only reason it wouldn't), I would seriously consider using an old-fashioned boring tool with a 1/4 HSS toolbit, ground to 60 degrees and held at 90 degrees by a setscrew. Here's Harbor Fright's version, $16.00 http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=2456 Spend some time making a nice jig to grind the cutters to precisely 60 degrees and you'll be a happy guy, with lots of cash left over for some single-malt. Alan (24237)
Bob- That looks pretty good. My current project requires a .5" hole to be threaded though - so that may be a little big. I may try to make a cross between yours and something like this: http://images.amazon.com/images/P/B0000DD5Z7.01-A3TQ3OIW6NTQKL._SCLZZZZZZZ_.jpg Maybe a rod with a slit cut in in for a 1/4" bit ground down to 1/8" or so - then held in place with a setscrew. What do you think? (24248)
You can also use a small broken tap for a piece of round HSS or you can buy small round dia HSS bits. www.grizzly.com has them. I bored some grooves once thru a 3/16" hole using a HSS bit ground with a hook nose to suit. Just using 2 dial indicators for my "vision" into the hole...Bob(24250)
My set of standard double ended boring bars uses round 3/32" tooling for the 3/8 and 1/2" bars. Ground HSS bits work fine in these and have the added advantage that you can put some rake on them whereas the standard 60 deg brazed tools are flat topped. Really depends on your sharpening skills/setup, I made a tinker which makes it easy for these. Bernard (24254)
Kevin I threaded a 1/2 hole using a 3/8" boring bar. My bar uses 1/8" square HSS held in place with a set screw set in the end of the bar. It was a tight fit and I did have to grind a bit on backside of the bar to get enough clearance. If you use the round HSS tools it is easy to make your own bar by just drilling a hole crosswise through it. Drill and tap a hole in the end for a set screw. Has anyone tried making a forged bar out of a HSS tool. I read recently that they can be heated up and bent into shape. They are then hardened by heating to a white heat and quenching. No tempering is required. I'm thinking about giving it a try with a piece of 1/8" HSS. John (24268)
Bernard How does a tinker help to grind a threading bit? I thought it was for endmills and horizontal cutters. I'm considering one to sharpen the cutters for my Burke horizontal so any comments are welcome. I don't have the drawings, so I'm making one based on the pictures I've seen. Castings are done in Aluminum rather than CI. Thanks for any info, offline would be fine. John (24269)
John, One of the heads has a little turntable mounted on the end. It starts life as 1" barstock, one end is tapered 2MT the other is milled to a flat. A 1 3/4" turnbable is centered on the flat with a slotted bar screwed to it to hold lathe tools. I graduated the turntable 360, an exercise to test my CNC rotary table. In practice it works extremely well, as the grinding forces as very light, and will do until I finish my Quorn. Bernard (24270)
Do you think a piece of 12L14 would be sturdy enough for this? I would like to turn it down on one end to fit in my boring bar holder, then turn the other end down even more, flatten the top and bottom, then drill the hole for the HSS cutter similar to yours. I wasn't sure if 12L14 would flex too much or not. Kevin(24318)
Kevin, That's what mine is made from. I wouldn't turn it down any farther than needed. As already said by other members you will need different sizes. Bob (24319)
Bob I'll start with the size I need for now. I have several bars of 12L14 so once I finish this, maybe I'll make a set. thanks again, Kevin (24320)
A 3/8 boring bar from Enco is $4.75 and 6" long and has the broached holes for HSS tools. There are sets of many different types and sizes and lengths, and they are low cost. I would buy the bar, then make a fixture to grind the 60 deg cutter. My biggest problem was that the smaller bars used round bits not square, and I didn't have a means to cut the bits to length easily. Dave (24321)
Just a thought. Aren't most drill bits HSS? Might give me something to try instead of pitching ones that aren't suitable for re-sharpening. (24322)
Dave an easy way to cut the bits is buy a cheap $20 4 1/2" grinder either from HF or your local farm store and put on a cutoff wheel either 1/16 or 1/8th thick. And please use a vice when cutting. Don't be a Bob. Bob (24323)
Yes they are bit they get softer at the other end...Bob (24324)
Yes, but you can always heat treat them. Bernard (24325)
If you grind a ring around the bit where you want to cut it, then wrap a piece of cloth around the bit, fix it in the vise with the end protruding and hit it with a hammer. Bernard (24326)
I finished my threading bar - I haven't tried it yet so the results are unknown. I made it out of a 12L14 bar so it would fit in the quick change boring bar holder. I attached some pictures if anyone wants to critique it. Kevin (24416)
Kevin: Fine looking job!!!! Now you need to make one with the toolbit sitting at 45 degree angle and you can bore right to a shoulder. Ron (24417)
Ron! I didn't even think about threading internally to a shoulder! I'll have to give that some thought. Maybe the next one will be able to alternate between 90 degrees and 45 degrees. Kevin (24418)
1 1/2-8 Threads
I tried going to cut some 1 1/2-8 threads tonight and had all kinda of trouble with the gear train jumping out of gear. The fewest number of tpi I had cut before was 11-1/2 TPI and I did not have any trouble with those. I know that the fewer TPI the more strain is placed on the gear train. After having the trouble, I set the quick change gear box to 28 TPI and did not have any problems: it ran just fine. Has anyone had trouble cutting 8 TPI? Has anyone found cutting 8 TPI easy? Does anyone have any suggestions? Gary P. (25638)
Try slowest speed on spindle and lighter cuts. (25639)
For the major stock removal, try running a thin parting blade in at a 30 degree angle, first from the left, then from the right, or vice-versa, so as to hog out most of the thread and use the threading tool for the cleanup cuts down each face--this way is not to have to take the whole width of the thread face in one pass. But before all that, you do have the compound set to 29 degrees, right? (25640)
Piece of cake, with a lot of practice. I made 30 test parts before i made the cut I wanted. Now my back gear used to jump out I just snugged the right hand bolt on the rear of the headstock on the eccentric. I have lots of pics in my SB10k group. Bob (25641)
Gary, Not sure of which model you have but the 10L has an adjusting set screw on the headstock beneath each backgear eccentric. The one closest to the spindle is a friction lock and the one furthest away is the gear seating depth. First, check for any crud in the gear teeth and clean them if needed. Then with the motor off, engage the backgear and adjust the depth so it is just off the bottom of the gear. Next, tighten the friction stop. This should snug enough that it doesn't jump out of gear during a cut, probably needs to be tighter than it is right now. The 9 and 10K adjustment should be similar. Use a sharp thread cutting tool and only cut .005" each pass. JP (25643)
Are you using a HSS bit or an indexable carbide bit? Also, set your compound to 29.5 degrees (for a 60 degree thread form). Zero the cross feed and feed in with the compound. I usually take .020 the first pass then .010 the next, then .005 till the final couple of passes. Then its .002 to .001. I would run the same setting for the final couple of passes. Make sure your tool is at center. Use a thread cutting lube. Run in back gears at a slow speed. Still, sounds more like machine adjustment. Tom (25644)
Gary, Just wondered what location was it that jumped out of gear??? I needed a knockoff nut to protect the spindle threads on my 10K. Priced it from Leblond about 2 years ago and if I remember (that's a question at my age) the quote was $75. I found a scrap of 2 inch round in my scrap box and it already had the OD knurled!! I had a copy of the spindle threads on a short piece of AL which I used to test the threads as I slowly cut the ID threads of the nut. The one mistake was I cut the threads about 0.010 inch too deep but the register fits well and the nut is just for protection, so It works fine. I had NO trouble with the quick change and associated gear drive. Darrell (25665)
Darrell I had trouble with the back gears jumping out of gear, The forward reverse level on the gear train jumping out of gear, and even the drive gear in the banjo jumped out of gear once. I think I need to adjust my back gear engagement. I think my other problem is dirty gears. I flushed them out with Supper lube and they are working better but I need to clean them some more. The fewer number of threads per inch is cut the more stress that is put on the gear train. 11 1/2TPI is the fewest I had ever cut before. Most of the time I have cut 20 or more tpi and because there is less stress on the gear train they have worked just fine. Those gears in the gear box may have been cleaner because of more use. My lathe is 65 years old and I have owned it for 26 years but I bet no one has ever cut 8 TPI with it. Maybe the gears could use a little break in time. Gary P. (25666)
Screwcutting with compound set parallel to bed
For the past several years I have followed a method recommended by Martin Cleeve in his book 'Screwcutting in the Lathe'. Instead of setting the compound to 29 degrees I set it parallel to the bed and advance the cut by the cross-slide, at the same time move the compound by 1/2 the cross feed advance. To be precise the compound movement should be 0.57735 times the cross feed for 60 degree threads (tan 30 degrees is 0.57735), but for all practical purposes 1/2 is fine. Using this method I do not have to calculate the compound angle adjustment, and find it easy to independently clean up either the leading or trailing flanks without having to increase depthing. Bernard R (25885)
I've cut threads "manually" for many years on my sixty-year old 10-inch SB, with neither a thread indicator nor a reversing motor. (Truth is, the motor does reverse, but only by loosening some bolts and turning the motor end cap and brushes forward or back a few degrees!) Thankfully the lathe does have a single lever screw cutting gearbox. This screw cutting method is very old (it dates from before screw cutting indicators were widespread), and it's not as convenient as using an indicator, but it does work, and its definitely not rocket science. But I have no other choices with this lathe. The technique depends on keeping the three-way relationship between lead screw, lathe mandrel/spindle, and the lathe carriage/tool point. 1) My SB has a keyway along the lead screw, so I use that as a "marker" and engage the half nuts only when the keyway is clearly on top, at 12.00 o'clock, as closely as I can judge. 2) I mark the spindle or chuck and index this against a point on the headstock casting, a spot of paint or a felt pen mark on each will do the job. Again I use 12.00 as my reference point, but any convenient position will do. And the half nuts are engaged only when the spindle is in this position -- keeping its relationship with the lead screw, so both are set at 12.00. 3) The extra trick that makes this work is always to set the carriage moving at the same point along the lathe bed when the half nuts are engaged. To do this -- before cutting, and with the lead screw's keyway at 12.00, I move the carriage to a convenient place where the half nuts will engage easily (NO FORCING). And to ensure this position is used for the next cut, I put a 12-inch bar across the bed in contact with the carriage, bring up the tailstock to the bar, and lock the tailstock in position. When cutting a thread my procedure is to set things up like this, with back gears engaged so everything happens slowly enough for me to stay in control. A) The half nuts are engaged, the clutch is dropped, and I take the first cut. B) At the end of the cut I heave on the clutch, retract the cross slide, disengage the half nuts, and wind the carriage back along the bed with the handwheel until it contacts the 12-inch bar. C) Then I set the next cut, slip the clutch gently or turn over the lathe by hand until the spindle is at 12.00, and the leadscrew is at 12.00 -- at this point the half nuts engage sweetly. D) Drop the clutch into full contact and take another cut. E) At the end of the cut I'm back at stage (B), and the procedure starts all over again. As I said, its not as convenient as a screw cutting indicator, but it does achieve an accurate relationship between spindle, leadscrew, and carriage/tool point. Just don't force the half nuts into engagement -- the leadscrew and spindle must be set so that half nut / leadscrew clearance allows easy engagement. This takes as long to describe as to cut a thread. It's repetitious work, so I shut the workshop door while its going on, but there is nothing complex in the operation. With very worn and sloppy half nuts this method may not be able to work -- perhaps someone else's experience can say what the practicable limits are? Alan (25899)
Alan: Great post, I will have to try that. The funny think about a number of people posting that using the lathe's gearing to reverse while threading is, (If I remember right!) I have done it and it worked. (May be I was lucky) I bought a thread dial gear from one of out list members last year but have not gotten around to building the rest of the threading dial. So I just leave the half nuts engaged while threading, and run the motor in reverse. Your method may be faster. Gary P. (25900)
I don't quite understand your use of the clutch while cutting threads. An interlock prevents the half-nuts and the longitudinal power feed (through the clutch) from being engaged at the same time. What am I missing here regarding your method below? Arne (25902)
Alan, I've read about this method, it was referred to as 'repeat pickup from chalk marks', the problem the author found with it was that he had to manually turn the chuck or spindle to check that the spindle and lead screw marks were the correct combination. Do you manage to do this under power? Bernard R (25903)
Alan, Thanks for the advice. I have made a copy of your instructions and will give it a try. Paul (25904)
Paul, return your cross-slide to same position and advance your compound a few thous, and start a new cut. I have a cross slide stop for my SB to make sure the cross slide returns to the same place every time. If you are off a couple of thous. ether way on the cross slide return it will screw everything up. Make all adjustments with the compound. Duane (25905)
Bernard, I admire anybody who can keep their concentration engaged well enough to make that method work for normal screw-cutting. About the only time I ever risk anything like it is when trimming an ACME thread to fit a worn nut. An operation only risked on good days when I'm feeling exceptionally serene, carried out with the workshop door firmly locked and the big Don't Disturb sign out. For normal purposes I prefer to use angular in-feed with zero-zero collar setting as advocated by, among others, George Thomas. The great advantage of this method is that no in-feed or set-up calculations are needed, just flank angle, thread depth and TPI. All straight out of the ZEUS book. The method starts with the top-slide set at an angle of a couple of degrees less than the thread flank angle so that a shaving cut comes off the trailing edge even though the leading edge of the tool does most of the work. Then manipulate the cross and top slides so as to bring the tool tip up onto the work and set both feed indicating collars to zero. Wind the saddle down the bed to get the tool clear of the work and move the top-slide forwards by the specified thread depth. Set the top-slide collar to zero. Wind the top-slide back far enough to clear the work-piece and bring the tool up to the start of the thread. Ensure that the cross-slide is still set to zero and apply a suitable first cut to the top-slide. Use the cross-slide to withdraw the tool for clearance to run back at the end of each cut, apply a suitable in feed to the top-slide and return the cross-slide to the zero setting before the next cut. At the end of the job the collars on both slides will read zero. Its even easier if you have a positive stop for the cross-slide, like the factory doobie on my Heavy 10, as then you don't have to watch the dial when resetting the cross-slide for the next cut. (25907)
Bernard Nope, not under power. I try not to poke my fingers into a lathe under power! Aligning the spindle and leadscrew marks and setting the carriage start position are something I do by waggling things around by hand -- this could be a lot harder with a big lathe, old oil on the ways, cold oil in the headstock, etc. Like I said, it's a method that works, but it also makes you realize why they don't build lathes like today. Alan (25908)
Arne Apologies for misleading you with my use of the word "clutch". I simply let the flat belt drive go slack and allow it to slip so I can gently turn over the lathe -- its a cheap substitute for a clutch between the motor and spindle. Alan (25909)
Looking for a source for a threading tool
I need to single point some I.D threads. In the past I used a tool that had a piece of carbide brazed to the end of a 1/2 shank. Do you know where I can get these threading tools. I tried MSC and Enco but all I see is insert tooling. Barry (26198)
I recently needed the same thing. I just made one out of a piece of 12L14 I had laying around and a ground down 1/4" HSS bit. Here's what I did (the pictures are lousy, I know). Kevin (26199)
Have you checked J L Industrial? The picture looks like a Bokum tool. Check with Bokum. -Bruno (26200)

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