Lathe - Thread Cutting - Metric



Metric threading info (May 16, 2001) Metric threads (Mar 25, 2003)
Metric Thread Questions (Jul 25, 2001) Cutting metric thread with a 2 lever QC gearbox (Jun 2, 2003)
Metric threads for 9" SB w/ QC gearbox chart (Oct 24, 2001) Metric Transposing gears on English screw thread SB (Sep 21, 2003)
Metric gearing charts (Oct 26, 2001) Metric Threading Question (Dec 27, 2003)
Cutting metric threads without metric gears? (Mar 3, 2002) Simple Metric Threading (Feb 26, 2004)
13" SBL metric thread chart (Aug 6, 2002) Metric threading (Feb 12, 2005)
Cutting Metric Threads (Aug 26, 2002) DP and Metric Module Threads (Jan 30, 2005)
Metric Thread Cutting (Feb 1, 2003) Threading Gurus (Metric) (Feb 9, 2005)
Metric threading info
A thread ran last week on this list about metric threading on 10" SB heavy-10. I will eventually get around to posting a gear combination vs. pitch list as shown on the placard of my metric transposing gear kit. Until then, the info on this website may satisfy your immediate needs: http://lathe.com/metric_threading.htm Mark (647)
Metric Thread Questions
I was wondering if there are some metric threads equivalent to US standard threads? Are there any web sites that that have this information? I'd like to see a "side by side" chart or table if possible. I have a 9" SBL Model A and will have the opportunity to cut some metric threads on it in the near future. At this point I don't know the thread requirements. According to the reading I've done, it will take zillions of transposing gears to cut metric threads on an "inch" lathe. Well, maybe not quite a zillion, but quite a few. Jim (1183)
Some metric threads may be close to an inch-based thread, but never exact. Keep in mind also that metric threads are denoted by their LEAD (advance per turn), while imperial threads are denoted by the inverse of the lead (number of turns required to advance one inch). We might also want to review some terms. LEAD is the distance a screw thread will advance in one revolution of the screw. PITCH is the distance between crests on a screw thread. The value of these two items will be the same for a single start thread, but not for multiple start (double, triple, quadruple etc.) threads. As to the gears required, it may not be as bad as you fear, especially if you do not have a long thread engagement, or some other reason to EXACTLY duplicate the lead. Often, using other gears, you can come VERY close to the required lead, within a couple of 100ths of a percent lead error. This mathematical error may be less than the error in your lead screw. Here is some information for cutting metric threads on Logan Lathes (similar to the South Bend): http://lathe.com/metric_threading.htm  http://loganact.com/tips/met-thd.htm  I'm sure others will have more suggestions, but this should get you into plenty of trouble while you wait. Scott Logan (1184)
Scott, Thanks for the very informative reply and links. Will take me a while to "digest" it all! Jim (1186)
To determine the pitch of a metric thread in inches: mm/25.4 To determine the pitch of an inch thread in mm: inches x 25.4 To convert between inch pitch and TPI: 1/inches = TPI, or 1/TPI = inches. This leads to: 25.4/TPI = mm. 25.4/mm = TPI If you don't find a ready made chart listing the pitches in sequence you can certainly generate your own, especially for the pitches in which you are most interested. I have a 9" SBL Model A and will have the opportunity to cut some metric threads on it in the near future. At this point I don't know the thread requirements. According to the reading I've done, it will take zillions of transposing gears to cut metric threads on an "inch" lathe. Well, maybe not quite a zillion, but quite a few. You will certainly need the transposing gears, which I believe are usually a combined 120/127 gear. This has the effect of making the screwcutting train treat the 8 TPI leadscrew as if it were a 3 mm. pitch. It's not clear to me whether you need additional gears, "How to Run a Lathe" doesn't appear to cover cutting metric threads on an inch lathe with a QC gearbox. The Atlas manual does do so for Atlas lathes. Some participant of this group may have a chart telling you the gear train required and the QC box setting for various metric pitches. Any volunteers? Also, if you were to tell us the metric pitches in which you are most interested we might be able to work out the appropriate setups. In this regard, I need to know the existing setup on the stud, intermediate, and gearbox input gears. Anthony (1188)
Anthony, Being a newbie to lathe work, transposing gears and metric threads is a bit overwhelming, but an interesting challenge! The first thread I will have to deal with looks to be 37/64's in diameter and nearly fits a 24 TPI gauge. Right handed thread. I've been studying the metric screw threads chart (p.64, How to Run a Lathe), with MAGNIFYING GLASS IN HAND, and it appears that several of the metric threads can be done if I obtain 127T and 100T gears. The current gearing I have is: 20T stud, 40T stud (extra for lower TPI's) 80T idler 56T on gear box If I add 127 and 100 gears to the mix, what the heck is the affect on the QC gear box settings? How do you know which setting to use? Might be simpler to just buy a metric lathe! :-)) Jim (1190)
It would appear you are cutting a 1mm thread (25.4 TPI, pretty close to 24 TPI). Leave the 20T gear in the stud gear position, driving the 127T gear. This should be on the same stud as a 100T gear, which will drive the 56T gear on your gearbox. Take a look at http://lathe.com/metric_threading.htm#Diagram Set the gearbox to 20TPI, and you should be set correctly. TAKE A TEST CUT ON A PIECE OF SCRAP FIRST! You can also use a 37T and 47T gear in place of the 100T and 127T gears. The resulting lead error is approximately 0.003" per foot.  Scott Logan (1191)
I have no immediate requirement for metric or odd-ball threads, but I'm looking forward to making some extra gears for my model A in order to do just that. You never know when you might need to cut 1mm or 27 TPI. I recently picked up a 16DP gear cutter (#3) and when I get my dividing head going (making a replacement crank arm and lock-pin), I think I'll try making some special gears. Anybody know if aluminum would be strong enough for infrequent use or will I need to use steel? Since the cutter is for 35-53 teeth (or something like that) any gears that deviate from that range will be improperly formed unless I resort to a single-point form tool. With aluminum, I wouldn't worry too much about the fit for this application, but it has to be strong enough for operation. Paul R. (1193)
Paul 6061 or 7075 to T6 will work very well. I made a replacement gear for one of our grinders to replace a phenolic original about 4 years ago and it has shown no wear at all in use 16 hrs. a day 6 days a week use. And I think we should give Scott a big thank you for coming in with very good information that would be very hard to find with out his help. JWE (1194)
Paul, I have been using 6061 for special gears for years. It stands up very well. Be sure you keep them lubed well, they will wear out a steel gear they are meshed with if you don't. (1195)
Scott, I've been trying to digest as much of it as possible. Now for the big question (in my mind anyway)...how did you arrive at the 20TPI gearbox setting? With this configuration: 20T stud 127T 100T 56T (on QC gearbox) What is the pricing for your 37T and 47T gears? I think I could live with .003" per foot! Jim (1196)
Jim M wrote: If I add 127 and 100 gears to the mix, what the heck is the affect on the QC gear box settings? How do you know which setting to use? The lathe will treat the 8 TPI leadscrew as if it were 2.5 mm. lead. To understand what's going on here, the formula for the conversion is: Drivers/Driven x inch pitch x 25.4 = mm. pitch. The simplest example is (40/127) x .125 x 25.4 = 1.0 mm. This can also be written (40 x .125 x 25.4)/127 = 1.0 mm. Alternatively, (40 x 25.4)/(127 x 8) = 1.0 mm., where 8 = TPI of leadscrew. If you want to know the effect of substituting any other gear for the 40 divide new gear by 40 ( y/40 = mm. ). So, 100/40 = 2.5, 120/40 = 3, etc. Obviously, if you use a leadscrew other than 8 TPI this formula needs to be adjusted. I see that Scott Logan has already dealt with the 1.0 mm thread which it appears is you're first metric problem. Using his example, where the gear train looks like: A | C--B | D-------E with A = Stud Gear, B = Driven on intermediate stud, C = Driver on intermediate stud, D = Driven on Gear Box, and E = Gear Box setting, Scott's suggestion was 20, 127, 100, 56, and 20, respectively in the A, B, C, D, and E positions. Using his alternative 37/47 gears the sequence would be 20, 47, 37, 56, and 20. In fact any setup A, 127, 100, 56, E, or A, 47, 37, 56, E, where the values for the tooth count of A and the TPI setting of E are equal would work for you. You can also set it up as 20, 127, 120, 56, and 24, and there will be many other solutions. I have no argument with Scott's suggestion, I'm just trying to illustrate that there are many ways this problem can be solved. I hope this isn't too confusing for you. My position is, the better you understand the mechanism, the easier it will be to come up with your own solutions. Anthony (1197)
Anthony, at the risk of confusing myself and possibly others, I'll ask a couple of probably stupid questions. By the way, thanks a lot for trying to explain all this. Questions for your "simplest" example below using the conversion formula: 1)What is the source of the "40"? Is that the 40T extra stud gear in my gearing setup? 2)Is the ".125" a constant when using the standard 8TPI lead screw? 3)When substituting "drivers/driven" gears in the formula, are ALL drivers and driven gears included? Is this a decimal number adding all driver gears DIVIDED by all driven gears? Might be easier to purchase a die and do it manually! But then, there wouldn't be much satisfaction in that! Jim (1200)
There have been a couple of requests for prices for our change gears. With the indulgence of the list owner, I can provide the following information. First, before ordering any change gears from us, please check the following page to compare dimensions. Please be sure to compare the "DP" or Diametral Pitch. http://lathe.com/Change_Gears/index.htm  If you have any other questions, feel free to contact me privately. Scott Logan (1201)
Jim M wrote: Questions for your "simplest" example below using the conversion formula: 1)What is the source of the "40"? Is that the 40T extra stud gear in my gearing setup? It's part of a simple mathematical ratio between .125" and 1.0 mm. The fact that one of the standard gears provided by SB happens to be a 40 is a coincidence. I used the 40/127 ratio only because it should be simpler for you (or anyone) to figure what alternative gear would be appropriate for a different metric pitch when starting from 1.0 mm. rather than 2.5 or 3.0 mm. 2)Is the ".125" a constant when using the standard 8TPI lead screw? Yes. If you had a 16 TPI leadscrew the value would be .0625, 6 TPI would require .16666666 A x B x C --------- = X D x E x F where A, B, and C are drivers, and D, E, and F are driven gears. This can be extended as far as is necessary. Anthony (1204)
Answering Jim M.'s question: Questions for your "simplest" example below using the conversion formula: 1)What is the source of the "40"? Is that the 40T extra stud gear in my gearing setup? I wrote: It's part of a simple mathematical ratio between .125" and 1.0 mm. The fact that one of the standard gears provided by SB happens to be a 40 is a coincidence. I used the 40/127 ratio only because it should be simpler for you (or anyone) to figure what alternative gear would be appropriate for a different metric pitch when starting from 1.0 mm. rather than 2.5 or 3.0 mm. Thinking about this today I realized that the response was probably not clear enough. I can only plead that I had not previously gone through the entire derivation, even for myself. As there are 25.4 mm. in one inch, in order to calculate the inch equivalent of 1.0 mm. you must divide 1 inch by 25.4 (1.0"/25.4 = 0.039370078 5 x 8 x .125 40 x .125 40 ------------------ = ---------------- = ----- x .125 = 0.039370078----" 127 127 127 which equals 1.0 mm. (Hope this doesn't get scrambled.) Anthony (1218)
Metric threads for 9" SB w/ QC gearbox chart
I have asked in the past about a metric gear setup for 9" SB lathes with a quickchange gearbox to no avail. SB's How to run a lathe has the setup for a non quickchange lathe. Here is the answer that only involves changing the stud gear ( you have to have 7 for the whole range) and a 56 tooth gear you don't change, that is plus the 100/127 combo gears that stay fixed. I would think it wise to fabricate another banjo to easily change from standard to metric. Anyway the chart that shows this is on pg 4 of the e-bay # 1647456759 that ended oct 14 at $314. I can probably make a copy of the chart if its gone. Now if you DYI guys wanted to make your own set, you can get the 18 DP-14-1/2 degree PA from the 2001 Wholesale Tool catalog (the cutters are not on the internet). Some sizes are discounted from about $23 by 30% and 40%. You only need # 2,3 4 that should run about $60. But for 1/6 the price above you gotta have gear blanks and alotta time. I would be tempted to do this but acquired a large set of 20DP Boston Gears from 20-120 teeth. So I only have to get one #7 cutter and cut my blank into a 127 tooth gear. 20 DP gears are not quite as strong as 18s but are more easily available. Boston Gear and MSC has 20s but not 18s. Walt (1960)
Walt, If it's possible, may I have a pic of the chart of the gear settings for the metric quickchange SB9? Jordan (1961)
Jordan asked for the chart for above subject. Go to www.ebay.com and click on search, then click on search by number. Type in 1647456759. Print out page 4 for the chart labeled Metric Transposing gear chart. Worked for me. Walt (1964)
Walt writes: X (stud gear, read from chart, 40 or 20 for inch) | 100--127 (compound metric or idler gear) | 20--56 (QC box) In this setup the 100 and the 20 are just spacers. The process to convert from inch to metric is: 1. Slack the bolt that holds the banjo in position and swing it out of engagement with the stud gear. 2. Slack the nut on the idler stud and slide the 127 out of engagement with the 56. 3. Dismantle the 20--56 from the QC box, reverse their positions (thus 56--20), and reinstall them on the QC box. 4. Slide the 100 on the idler stud into engagement with the 56 and retighten the nut on the idler stud. 5. Install whatever "stud gear" is called out on the metric chart for the thread you want to cut. 6. Swing the banjo up so that the 127 engages with whatever stud gear is now in place and retighten the banjo clamp bolt. You're now ready to cut metric gears. The conversion back from metric to inch should be self evident but if requested I will write it out in the same manner as the inch to metric conversion procedure above. Having a second banjo will accomplish virtually nothing. You'll still have to remove and reverse the 20--56 QC gears, you'll have to remove the "inch banjo" and replace it with the "metric banjo", you'll have to change the stud gear to whatever is called out on the chart, and you'll have to re-mesh the gears. It doesn't appear to me that you will have saved anything. Anthony (1969)
Metric gearing charts
I've uploaded to the techinfo section, all the metric gearing charts I have including the one for English threads on a metric-leadscrew lathe. It seems the 127t/100t transposing gear is common to all lathes with an 8TPI leadscrew. metricchangegear2.jpg is the odd one out, dunno what lathe it came off of. (1977)
Having looked at all these charts ( and some others) It looks like all of the charts show change-gear type setups to get the metric threads. What is the procedure and settings for getting metric threads with a quick change gearbox - Does anybody know what setting for the box is used with the gear changes, and are any of the other gearbox settings useful for metric threads not attainable with the gear changes shown? Do any of the quick-change model books or manuals indicate for the later models what settings to place the gearbox into for use with the metric transposing gears? (1978)
It has always been my understanding that metric transposing gears are designed to alter the lead screw pitch first to a specific metric pitch and then the additional gear inserted in the train on the banjo gives you the actual metric pitch to a very small error. Thus with a QC gearbox and a 8tpi lead screw you would set your QC to 8tpi and the transposing gears will give you the metric thread. If I am wrong maybe Scott Logan will jump in with more detailed info as he has been of much help in getting correct information posted in the past. JWE (1979)
Machinery Handbook in later years ( I think it was # 42) had a several page description how to set up lathes to cut any thread with the right gear changes. Walt (1989)
This one shows the settings for an inch QC box with the gear train subbed for metric threads: http://groups.yahoo.com/group/southbendlathe/files/Techinfo/metricgearchart.jpg  This one shows the settings for a change gear (non-QC box) machine having an inch-pitch leadscrew being used to cut metric threads: http://groups.yahoo.com/group/southbendlathe/files/Techinfo/metricgear2.jpg  In this JPG, the chart on the right I believe is identical to the one in metricgear2.jpg. The chart on the left, which unfortunately did not scan well and is too fuzzy for me to read, is for a change gear (non-QC box) machine having a metric-pitch leadscrew being used to cut inch threads: http://groups.yahoo.com/group/southbendlathe/files/Techinfo/9-inchmetricgearing.jpg Anthony (1993)
I'm not Scott but I thought I'd try to contribute to understanding of the mechanism. In essence the transposing gears make the lathe respond to the inch pitch leadscrew as if it were a metric pitch leadscrew. In the case of a 100 driver and a 127 driven gear, if the 100 turns through one revolution while it is meshed wit the 127, the latter will turn through 100/127 of a revolution. On a .125" pitch leadscrew (8 TPI) if the leadscrew were rotated one full revolution it would move the carriage, via the engaged split nuts, .125". If the leadscrew is rotated only 100/127 it will drive the carriage .125" x 100/127 = .098425---" which, if multiplied by 25.4 to get the equivalent in millimeters, = 2.5. Therefore, the 100/127 transposing gears, when used with an 8 TPI leadscrew, give the effect of a 2.5 mm leadscrew. If you try the same procedure with 120/127 gears you will get 3 mm, 80/127 will give 2mm, 50/ 127 will give 1.25 mm, 40/127 will give 1mm, and so on. You can select the transposing gears to come up with whatever apparent metric pitch is convenient for your purposes. Going on to the second part of your statement, if you were to do this (set the QC box equal to the pitch of the leadscrew, then reset the gear train for each metric thread you wished to cut) you would be using the lathe as a pure change gear machine for metric threading purposes. While it's possible to do this it's inefficient. If you look at the inch to metric chart for QC box you'll notice that besides changing the stud gear the third column tells you to change the position of the left lever between positions A, B, C, D, and E. This controls the range, like the difference between cutting 8, 16 or 32 TPI. The fourth column mostly uses the number 1 hole (8 TPI) but in some cases uses the number 3 hole (10 TPI). This means the gears inside the QC box are being used for additional compounding to provide additional metric threads that would otherwise be difficult to get because of the relatively simple gear train used by most lathes intended for amateur or light industrial use. So while you commonly only think about changing the exposed gears in reality you have to consider all the gears in the train between the spindle and the leadscrew as well as the pitch of the leadscrew itself. Change any element in that sequence and you change the result or you have to change another element to cancel the first. To illustrate, on a non-QC box lathe with an 8 TPI leadscrew, this setup: 24 | 80 | 72-----leadscrew will result in a 24 TPI thread. So will: 24 | 36--54 | 48---------leadscrew The point being there's often more than one way to achieve the desired result. I do not by any means pretend that I know as much on the subject as Scott and am not trying to step on his toes. In fact I'd welcome any input he has on the subject. Sometimes different people state the same thing in different ways and sometimes those differences can help to clarify the situation. Anthony (1994)
Cutting metric threads without metric gears?
I've been watching eBay in hopes of finding a set of metric transposing gears for my 10k, but having no luck. (Anybody have suggestions of other places to look for used? I'm trying to avoid paying the full new price from South Bend but may just have to bite that bullet.) Meanwhile, I have run into a couple of items that I need to make metric threads for. The first was a 1.25mm thread that I was able to fake by using 20tpi. Given that the part only needs to engage 8-10 threads, the pitch was close enough and the part is now in service. The same solution will not work for the next part, because it's a 1mm pitch. I made a test piece at 26tpi just to see, and the lock nut works fine (only 5 threads) but the main part needs to engage ~20 threads and the thread mismatch binds before it gets anywhere close. Now to the question: I remember reading, either here on the list or possibly in Home Shop Machinist magazine, a process for using a metric tap in place of a lathe bit to cut threads but I can't find the article -- how would I control the cross feed speed to make this work? I think I remember something about the tool self-feeding after the initial cut, so maybe the tap riding in the thread just *pulls* the cross feed? Tim (3497)
I have cut dozens of metric threads without any metric gears by calculating a close match using standard change gears. I normally use my craftsman/atlas 6inch lathe for this task, only because I spent a day about 15years ago figuring out all of the possible gear combinations that could be used on my lathe and what the lead movement (how many millimeters/revolution) was. I made a little chart with all of the common metric thread leads, 1.0, 1.25, 1.5 etc and what change gears to use to get the closest cut. Most are only off a few percent and I have never cut one that did not work. The only drawback is once you start cutting you have to leave the half nuts engaged, stop the motor withdraw the tool and back the carriage up using the motor in reverse before making the next cut. This is not a big deal but it does take a little more time. If I were cutting metrics every day I might do something different, but making one every month or two does not justify spending a lot of money for me. Dallas (3513)
Are there gear/threading combinations that you can make with change gears that you can't make with a QC gearbox? Would you please post some of the combos you came up with that are close equivalents? I am curious about making equivalent metric threads. However, I don't feel it merits my buying the metric transposing gear set. Jon (3521)
At least on my Atlas with the loose change gears there are more combinations then on the QC models. The Atlas manual has tables for close approximations of metric threads as well as gearing for winding wire coils and other strange uses. I am not sure if the Southbend is the same but would expect it to be similar. John (3523)
Dallas, I was looking at Tony's lathe website from the UK, and found an interesting downloadable program to calculate threading pitches for a variety of change gears: http://www.lathes.co.uk/latheparts/page6.html The program is towards the bottom of the page. Jon (3565)
13" SBL metric thread chart
The 13" has a 6 tpi leadscrew whereas the 10L has an 8 tpi. So things are a little different. Rather than the 56 tooth idler gear (I think that is what they call it on the 10L 13??) the 13" uses a 64 T gear along with the 127/100 T gear. You change out the stud gear. For a short time I have posted some pics of the 13" metric threading gear chart that I recently sold on ebay at my webspace. Actually should be same for all 6 tpi leadscrew SB lathes-I think? (5615)
Has anyone found these gears on the open market like at Boston Gear? Jim (5622)
Jim The real issue in terms of gear availability is the diametral pitch (DP) of the gears (that is, the tooth size) in your standard lathe configuration. The new 127 and 100 tooth gears need to mesh with the existing stud and gearbox input gears, and that means they need to be the same DP. I don't see any clues on DP for the 13" in my 10"/13"/14.5"/16" parts list. At least one of your stud gear choices is I believe 48 tooth. If so and it is 16 DP (the size Boston Gear sells), the OD (over the ends of the teeth) will be very close to 3.125". If my guess is wrong on tooth count, measure any gear you can find, divide 16 into the number of teeth (count them) and add .125". If that is the OD (or very close) the gears are 16 DP and you can buy compatible 127 and 100 tooth versions from Boston Gear. If anything your gears will be larger tooth gears (i.e. smaller DP) than the 16 DP gears in the heavy 10". Boston Gear does sell change gears in larger sizes (but the next bigger size may be 12 DP), and I don't know if they have 127 and 100 tooth in that DP. On the topic of using my approach, the general approach (but not the specific answers) should work for any standard stud and input gears, and any lead screw TPI. You need to start back at the "pitch = 20/TPI setting" equation (which includes the combination of the standard stud and input gears as well as the lead screw thread, with the 127/100 combination added) and then do variations caused by different stud and input gears relative to the standard ones. I expect you will get a different set than I did for the 10L, and I can't tell if just 2 additional loose gears will allow cutting most metric pitches (as worked out for the 10L). Frank (5631)
Frank, It's a real pleasure reading your postings which are like lessons! I save them all! One of these days I want to start cutting gears using my 7" SBL Shaper. Back about 20 years ago I had a 10K that I bought at an auction that had a few teeth missing on the small gear that was part of the spindle assembly itself. I found a Boston Gear that was a perfect match and I machined the gear off of the spindle and also off of the ID of the Boston Gear. I made it a press fit using Loctite RC-35 on the shoulder and it ran quiet and to my knowledge is still running today. I remember that the DP was the same. If you ever get a chance I'd like a copy of your revised Excel spreadsheet you made up regarding the metric gears. Looking forward to your next posting. Jim(5632)
Cutting Metric Threads
I have to cut a 15x1.5MM external thread on my 9"SB lathe. I have cut many threads before, but never metric. I have the transposing gears and the chart for metric threads. My question is this, on what line do I start the thread on my threading dial? Joe (6016)
It doesn't matter where you start on the threading dial. When cutting metric threads using conversion gears, you can't disengage the half-nuts at all. You need to make a thread cut, then back out the cross-feed, reverse the lathe to return to the beginning of the cut, then advance the cross-feed a bit further and make another cut, etc. Frank (6017)
Suggest you do not disengage the halfnuts from the leadscrew until you have finished cutting the thread. Phil (6022)
The dial wont work on metric threading. There are metric dials, but they are complicated. If you only have one thread to make, the reversing method will suffice. If you are making more parts you may want to remove your thread dial and put the carriage stop on the right side. It must be set an integral number of threads (leadscrew) from your stopping point. There was an article in HSM recently that described the technique. The distance must be divisible by both the metric and us dimension. I will look for it tonight when I get home. RC (6024)
Metric Thread Cutting
Having spent many months lurking and trying to digest all the great information generously supplied by JWE and others I have a question that I have been unable to find an answer to. ( I have many others!) Some months ago I purchased a Boxford AUD lathe which is a Southbend Clone. It has a 3mm Metric leadscrew and Norton quick change gearbox. The manual states that the "Metric Thread Dial indicator uses two gears in order to assist cutting 20 of the most popular ISO metric pitches. An adaptor block is provided to give the correct position for meshing either of the gears as indicated on the chart supplied." It then goes on to say ....."The first cut should be taken with the dial in the A position and then subsequent cuts at any of three positions as indicated on the chart." (A is common to all pitches and there are 4 other positions marked B, C, D and E) The problem I have is that I do not have that chart and I have been unable to find it on the net. Until now I have had to survive with trial and error. Can anyone please point me in the right direction as to where I may be able to get hold of this chart? Gordon (9021)
Gordon The South Bend book "How to Run a Lathe" has a description of the SB metric thread dial, including a rendition of the associated chart (or at least my 1954 edition does- I didn't check any others). It appears to have 4 letter choices A, B, C, and D, where your Boxford has 5. The SB metric thread dial also has 4 different gears on the bottom (selectable as to which runs against the leadscrew for the pitch to be cut). This seems to differ from your Boxford description, which you say has 2 gear choices. However it looks like the SB version covers 46 different thread pitches, where you say the Boxford covers 20, so perhaps the Boxford's 2 gears are a subset of the SB's 4 gears. However, that doesn't get us past the 4 versus 5 letters. I don't know if a copy of the SB info would be much help or not. I don't have a scanner to get a copy of that page to you, but perhaps someone in New Zealand has a copy of "How to Run a Lathe", from whom you could get a copy, or someone in the US with a scanner may be able scan the page if you think it might help. It also looks like the Boxford is a close relative of the SB, but perhaps not quite a "clone". Frank (9024)
Frank, this Boxford was manufactured about 1978 so maybe that has something to do with the difference in reference marks on thread dial indicator. Gordon (9040)
Gordon, I just purchased a Boxford VSL 500 3 weeks ago. Its a metric machine. I have not even hooked it up to power yet. (It was under power and I ran it before I bought it) If I can help (9065)
If I can help ,mine has a thread chart, it has a Boxford gear box. Later, Dave (9066)
Dave With a bit of luck you will have the same gearbox and leadscrew as me. I have the chart which shows all the the pitches from the various gear combinations (this is attached to the face of the gearbox) what I don't have is the chart which relates to the thread dial indicator. Gordon (9068)
I contacted Boxford in the U.K. and they very kindly sent me the Thread Dial Indicator Chart. At some stage I will try and upload a couple of photos for comparison with the Southbend. Although it is a comparatively late model I'm sure most of you will recognize it. Gordon (9086)
Metric threads
There's been a lot of discussion re gears for metric threads - I admit I haven't followed it but now suddenly need to turn a 0.6 pitch metric thread on my 10K with quick change box and English lead screw. The chart shows I need a 24 tooth stud gear and a 100 tooth screw gear. Can anybody confirm that this is correct gearing for a 0.6 pitch metric? Practically, could I substitute a 40 or 44 tpi thread and have it work? Also, does anybody have these for sale? Frank (9874)
Valley chain and gear in southern CA 760 744 4200 should be less then $100 for both as long as it's a 20 or 16 DP. Kerry (9878)
You haven't given us the complete story. If I tell you to install a 40 stud and a 56 screw gear on your QC lathe, what pitch will it cut? Nothing unless you engage the gearbox and if you do engage the gearbox the pitch will be dependent on what settings you select on the gearbox. The SB metric transposing chart I have shows 48 stud driving 127 on the conversion gear with the 100 on the conversion gear driving a 56 screw gear on the gearbox. Then you select the C3 position on the gearbox which I believe is the 40 TPI position. The setup you gave (24-idler-100) should give 0.6096 mm if you were to engage 10 TPI on the gearbox, equal to 1.016 times your desired pitch. Only you can decide whether this is acceptable to you. Practicaly, could I substitute a 40 or 44 tpi thread and have it work? Using the standard SB setup for the gearbox (40-idler-56) 40 TPI = .635 mm or 1.058333 times your desired pitch, 44 TPI = .572727 mm or .6921212 times your desired pitch (3.937% short). Again, only you can decide whether either of these is acceptable. Regarding the acceptability of a thread close to but not equal to your desired pitch it would help a great deal if we had an idea of the application. As a leadscrew or feed screw, none of the above would seem to be acceptable. To engage 20 pitches of an existing nut would probably also make them unacceptable. If you want to engage 3 pitches of a lightly loaded non precision device they might be okay. Just keep cutting the thread a little deeper until it will engage with the nut. Care to give us a little more insight on your problem? Anthony (9886)
I said: The SB metric transposing chart I have shows 48 stud driving 127 on the conversion gear with the 100 on the conversion gear driving a 56 screw gear on the gearbox. Then you select the C3 position on the gearbox which I believe is the 40 TPI position. I should have said select the D3 position. Sorry for the confusion. Anthony (9887)
Cutting metric thread with a 2 lever QC gearbox
Having here a SB9 A with a normal 2 lever QC gearbox also having now a 127 tooth gear, if I understand correctly, I have to make a Compound Gear from the new 127T and a 100T gear that is no problem, the problem is which pos. of the levers creates which metric threads ? sorry for the bad English. Bert (11692)
Bert, Others may have sent you the information. If so, here's another copy. Anthony (11705)
Bert As you can see from Anthony's post you need some extra gears as well as the 100/ 127 to get the full range of metric pitches. If you just need standard bolt pitches to "nail" something together you can get near- enough approximations for most of the pitches by selecting selecting an appropriate TPI and driving the gearbox either via the standard idler or via the 100/127. Assuming the spreadsheet I hacked out years ago for this very purpose is right and defining near enough as less than 1% error the only pitches used on bolts between 2 and 22 which cannot be approximated are 1.75, 1.5, 0.75. This is 12 mm, 10 mm and 4,5 mm in ISO metric coarse and 12 to 22, 6 7 in fine. Less than ideal but useful in emergencies. I can send you the spreadsheet if you like but it needs checking 'cos I never actually used the data myself. Clive (11725)
Clive Could you send me the spreadsheet also? Some day I'm gonna try metric threads and it would come in handy. I am all Mac so will have to download on a friend's computer, but that'll be OK If you could, I would be grateful. Frank (11727)
Metric Transposing gears on English screw thread SB
I have a South Bend 10K Model A machine. Originally this machine was ordered with the accessory Transposing Gear set. I do not have the set, but fastened inside the left hand head stock gear cover is a plate titled: Metric Transposing Gear Chart Metric Threads*English Lead Screw*8 Threads Per Inch This chart has a part number of PT 1543NR2. The chart has four vertical columns of info: MM/PITCH (shows a pitch range from 6.00 to 0.20) STUD GEAR (lists gears 26T thru 48T) PLUNGER HOLE (lists A thru E) PLUNGER HOLE (this column lists either a 1 or 3) THIS IS THE ITEM THAT I NEED HELP ON. WHAT IS MEANT BY PLUNGER HOLE 1 or PLUNGER HOLE 3? On the far right-hand side of the plate is a single gear diagram showing the stud gear, the 127T/100T gear and the screw gear as a 56T. This chart is not shown anywhere in my South Bend literature or catalogs, only on the machine. My lathe was mfg. in 1967 according to the SB factory. Perry (14108)
The plunger hole refers to the position of the levers on the gear box. If you look at the gearbox plate you will see the letters and numbers. (14113)
Thanks for the comeback on the metric info Steve. Yes, I understand the A thru E positions on the gearbox because the gearplate is so marked, but my gearplate has no reference to numbers at all. I used to own a 9in Model A and it was the same as my current 10K, ie, A thru E denoted but no ref. to numbered holes or slots. So, I am still wondering about the #1 or #3 hole position. Perry (14114)
I am pretty sure that the numbers refer to the right hand lever on the gearbox. It makes sense as that is the only other plunger hole that would be involved. (14116)
Perry Column 1 is in fact the farthest left position of the right hand lever on the QC gearbox (i.e. the column for 4,8,16,32, etc TPI) and column 3 is the 3rd from the left (containing 5, 10, 20 etc TPI). It is not hard to show that with a 100/127 tooth transposition gear and the stud gears shown, the TPI settings needed for the Metric pitches shown are from those TPI columns. Frank (14118)
Frank. I am assuming that with the 127/100T gear in place, using the 56T gear on the screw drive, that I will be able to cut the threads indicated on the gearplate by using the designated stud gear and putting the plunger(s) in the indicated holes according to the gearplate attached to the inside gearcover on my 10K. One of the stud gears is the 40T stored (but not used) on the screw shaft ? This gearplate shows only one gear setup, using a constant 56T on the screw drive. This gearplate carries part # PT 1543NR2. does all that sound correct to you? Perry (14126)
Perry All that sounds right. The standard SB approach to metric conversion was to leave the screw gear (on the gearbox input shaft) unchanged from the US thread setup, adding the 100/127 conversion gear, and then changing the stud gear to various pitches, in conjunction with specific TPI settings on the gearbox (identified by the lever locations). One of the stud gear choices is usually 40 teeth. My experience is with the 10L, but everything you mention matches that lathe (except the 40 tooth stud gear stays on for all US threads on the 10L, rather than the 20/40 tooth swapping on the 9" and 10K). To double-check it is easy (and probably good practice) to set up the transposition gears and a particular stud gear and plunger combination from the chart and just cut a light thread in a scrap of aluminum or whatever else you have, and measure the pitch (either with a metric thread gauge or just a metric scale). Frank (14134)
A couple of years ago, I set up my South Bend 9" standard change gear lathe to cut metric threads. The way I did this was by following the information on Scott Logan's website. I cut my own 47/37 metric transposing gears (as a substitute for 127/100 transposing gears), and used a formula on Scott's website to calculate the gear trains. The formula was as follows; mm Pitch = 2.5 X (Stud Gear/Lead Screw Gear) Using simple algebra, this can be rearranged to look like this: Lead Screw Gear = (2.5 X Stud Gear)/mm Pitch Using this, it is easy to plug in a stud gear value and figure out the lead screw gear. I made a chart for most of the ISO Metric Standard Threads. The little 9" South Bend lathe has an 8TPI leadscrew. Now I am in the process of trying to help a friend set up a vintage 1895 "American" 12X36 inch lathe to cut metric threads. This lathe has a 6TPI lead screw. I have manufactured the 37 and 47 tooth gears in the correct pitch for this lathe, to be used together as compound metric transposing gears. I have been going in circles in my head trying to figure out how the formula needs to be changed to account for the difference in lead screw pitches. Is their a simple answer to this? I suspect that a 13" South Bend has a 6TPI lead screw. If so, maybe someone who has done this with a 13" SB lathe can help out. A metric gear chart for any standard change gear lathe with a 6TPI lead screw would probably help a lot. (14675)
I don't know what happened to my last response so I'll try again. All else being equal the tool on a 6 tpi will move 1.3333 times as far as it would on an 8 tpi leadscrew. If you used a gear setup that would cut a 1mm pitch on an 8 tpi, it would cut 1.333mm on a 6 tpi leadscrew. The simplest fix (I think) would be to add a 4:3 reduction in the gear train. Alternatively you could use a setup that would give you 3/4 the pitch you want. If you want 1 mm then use a gear setup that would cut .75mm on an 8 tpi leadscrew. John (14676)
Metric Threading Question
I have been following the metric conversion for threading posts with great interest. I'd like to do this on my 9" model A. A pair of 100/127 tooth gears just sold on eBay for $163, a little out of my range. My question is: As close as I can determine, my gearing uses 18 D.P. gears. Where can I get 18 D.P. gears? I have a Boston gear catalog, but they go from 16 D.P. to 20 D.P. What's also caught my eye was the fact that a 127 tooth seems to be an odd-ball. Any suggestions or comments? Or is this a gear combo straight from SBL? Ray (15974)
18DP is no longer a commonly made pitch. A 127 tooth in 18DP will be over 7" diameter. 22:28 will get you close as will 45:57 and other combos and be better sized for the machine. If you can't find them you may have to make them. MSC has 18DP cutters. JP (15976)
You can get the 100:127 gears in 32DP and finer pitch from http://www.sdp-si.com/ JP (15977)
Not quite as close. There are 25.40005108 mm to an inch 2*127/100 = 2.54 even. This is very close 2*28/22 - 2.54545454.... This results in 2% error. If the thread length is small this is negligible. For a longer thread it may be of concern. Its equivalent to 0.002" per inch. 2*57/45 = 2.5333133... This is a 2.6% error. again for short threads, no concern. However .0026 per inch run out. Jim B. (15980)
First: I am not familiar with the gear train on the "A" mode. The reversing gears on the "C" (and I would guess the A) are 20 DP. It may be possible to do your conversion by using a 22 tooth 20 DP gear keyed to a 28 tooth 20 DP and driven off the bottom gear of the reversing gear triplet to get the conversion. You would then need to convert to 18 DP. You could have two smallish ( 16 or 24 tooth) gears of differing DP and the same tooth count keyed together as an ideler. I believe I could do this on a "C" . I don't know about an "A". You would need to weight the cost of the three 20 DP gears and a single 18 DP purchased on e-bay, vs. the cost of the proper 127/100 combo. I paid about $12 for a 24 tooth 18 DP and about $20 for a 16 tooth 18 DP. I don't know how much Boston Gear charges for a gear. Just a suggestion. Jim B. (15981)
You have several solutions for you. The first one would be to make your own 127-100 conversion gear. You also need some stud gears. There is also the cheaper way: the 47-37 compound gear combination that gives an approximation close enough, not to worry about interference In Nov, I posted a small excel spread sheet with all combinations on the QC gear box that would give metric pitch. Everything was calculated with both 127-100 and 47-37 combination. You can see the error on few threads. All calculations were done to at least 4 digits. You found excessive $163 for the conversion gear? I have seen a full set of conversion gears go for $460 US on eBay last march. Good luck with your conversion. Don't forget that the lead screw cannot be disengaged when cutting metric thread. (you can always disengage but you need to re-engage it exactly at the same position. When I disengage, (close tolerances at the end of the thread because of shoulders) I re-engage on the thread dial on the same mark once the motor has reversed. You need a reversing switch or a handle to turn the spindle by hand. Guy (15982)
Sorry about your units but the definition of one inch is 1 in = 25.4 mm exactly I don't know where you found this figure of 25.40005108. Unfortunately I am not home and I don't have all my references. At the end of the 19th century or beginning of 20th century the inch was defined against meter kept in Paris. Guy (15983)
On my Model A, I found the following diametral pitch: 20 DP on the spindle end and reverser gears apron gears except the gear meshing with the rack under the bed 18 DP on the gear train leading to the gear box 16 DP inside the gear box. I have not checked the back gear and bull gear but I believe they are 16 DP. Guy (15984)
By act of congress there are 39.37 inches to a meter. 1/39.37 is 0.0254000508. 25.4 is not "exact" 39.37 is exact. The two are not quite the same. Jim B. (15986)
Sorry, the definition of one inch is, by act of US congress in ~1959, 25.4 mm. EXACTLY. http://standards.nasa.gov/metric_chart.pdf  http://www.quiltuniversity.com/metric_conversions.htm  The "proper" transposition gears for metric threading will always include a 127T (or possibly a 254T!) gear. You can get REAL close, by using a 37T and 47T set, which is accurate to ~2/100 of 1%, or about 0.003" per foot lead error. See: http://loganact.com/tips/met-thd.htm  http://lathe.com/metric_threading.htm  Scott S. Logan (15988)
Yes, my lathe has 20 DP on the spindle, but then goes to 18 on the change gears to the QC gearbox. After weighing my options, I decided to go with 3 - 18 DP gear cutters from MSC (thanks JP) to produce all the gears needed. That is: 127/100 combo, 56, 48, 44, 40, 36, 32(already have), 28, and 26T. This will allow me to cut any metric thread out there in the universe, I think (this always gets me in trouble). I have a L-W Chuck indexing head, so why not go for it for $77.00 worth of cutters. I learned the metric system some 35 years ago, and find it much easier to work with. I didn't mean to start any arguments on it's equivalents. I'm going to stick with the conversions on my TI-86 calculator. That is, 1 inch = 25.4 mm, 1 m = 39.3700787402 inches. Even though we live and excel in a world where things too small to see make a big difference, how close is close? My next challenge is that 6 milli-cubit pitch boat part. I can do it! (I like that one JP). Next question for Guy Cardin, and thanks for your input too. I downloaded the excel sheet. Great! With the thread dial indicator, can't I disengage the lead screw, back off and re-engage on the same mark? I'm probably a month ahead of myself, by the time I order cutters, make the gears and figure the whole thing out, but you got me curious. Ray (15998)
Ray, The old timers used to cut the involute profile on gears with a shaper/planer and a 29 degree cutter bit, any pitch and any number of teeth. Kind of neat to watch. http://home.comcast.net/~b.fill/Shaper_gears_01.jpg  There are 8 or so cutters for each DP, each one does a range of 'tooth count'. JP (15999)
Jim The common "small gear" alternative was misquoted. It is 37/47, not 45/57. 2*47/37 = 2.54054, or about .02% error, or about .0002" error per 1" of threads. This is close enough for most work. Previous poster (whose name I forgot) Having said that, I don't know where you would get either a 37 or a 47 tooth gear in 18 DP. Boston Gear will sell them in 16 DP (for less cost than the 127 and 100 tooth gears), but 18 DP is tougher. You may still need to roll your own. However 37 and 47 should be easier to make than 127/100. The blank is smaller, and most index heads (if you have or can borrow one) will get you to 37 and 47 steps, but not 127. Frank (16001)
The 127-100 conversion gear makes the thread dial indicator useless for disengaging, move the carriage to the beginning and re-engage on the same mark. The synchronization of the spindle cannot happen. If you are successful once, the next pass it won't happen. The best for you would be to experience it once You will see what happens. Every lathe manual are clear about this: How to use a lathe by South Bend, Manual of the lathe operation (Atlas) and many other machinist manuals. My alternate way is to disengage the split nuts while I back off the tool bit. I stop the spindle, reverse the rotation and re-engage the split nut as soon as the dial comes back to its original mark. This keeps my synchronization during the whole process. With a 3 phase motor, reversing would be much more efficient as the spindle can reverse instantly SB made a metric lathe(10K) that had a specific metric gear box, metric lead screw and a special thread dial. The pitch of the metric lead screw is 3 mm If ever you need to cut a 27 TPI, you will need a 54T gear or a 42T gear. However, I don't have my documentation here to tell you exactly the gear box setup. Guy (16006)
If you are thinking metric gearing think England. It is much more common there and fairly common for the Boxford ( SB clone ). The change gears needed are all commonly available ( part of the model C gearset ) except for 2 ( 26 and 28 ) and they are not used with common threads. I got the other gear later on eBay. The complete set of gears is composed of 127/100, 48,44,36,32,28,26 gears. I was able to get the 100/127 and a 28t from an English individual delivered for $140. G M Tools http://www.gandmtools.co.uk lists the 100/127 on their site for a reasonable price. All the above is for the 9 and 10k. The larger lathes may be a different story. (16013)
I have used G M in the past. The prices are reasonable, less than E-Bay, you are getting new product and the shipping is reasonable. Jim B. (16015)
Simple Metric Threading
My name is Rodolfo (68) and live in Argentina. I started learning to run a lathe at age of 14-18 on a SBL. Then, I worked in an European firm where all was metric. Lathes were Boley, Mikron, Schaublin, etc. and I use metric threading very often. I changed my business during long time and now I returned to the lathe. Last month I found and bought in my country a SBL 9" x 4? model 80A S/N 66202 built on 1935 in very good shape despite its 70 years old, with single lever quick change gear box, cross feed, legs, motor, follow rest, steady rest, milling attachment and a table for several purposes, but two oilers which I made plastic caps for its. To convert it to metric threading, I can't place 100-127 teeth gear because the only gear I can change is stud gear. No way to modify distance between centers. Well, I found that placing a 34 teeth 18 dp instead of the 48 teeth stud gear, I can cut pitches of 0.25, 0.45, 0.50, 0.75, 0.90, 1 mm, 1.5, 2.0, 3.0, 4.0, 4.5, 6.0, 8.0 mm with a gearbox setting of 72, 40, 36, 24, 20, 18, 12, 9, 6, 4.5, 4, 3, 2.25 TPI respectively, within a misalign of 0.04 of 1%, that is good enough for all practical purposes. I made it and placed it very successfully. I'd wish to share my "discovery" with you. Sorry my English. Capipio. (17481)
Capipio Thanks for sharing your joy with all of us. Clint (17483)
Capipio. Your English is great and so is your story. I enjoyed very much reading it. I had the pleasure of visiting your country many years ago. Russ (17484)
Capipio, Thank you for writing about the metric threading (I've intentionally left your letter below so we can remember it). I have a Model A 9" South Bend with the two lever QC gearbox. My stud gears are 40 and 20 tooth. Do you (or anyone) know what gear I could use to do the same thing as described below? The idea of being able to cut metric threads is extremely appealing. By the way Capipio, your English is a heck of a lot better than my Argentine. Dave (17497)
Dave, I believe he is referring to the gear mounted on the back of the spindle. The other option is to make up a 34/48 change gear and add it into the gear train from the spindle to the gearbox somehow. JP (17498)
Dave (and list) I'm afraid your case is not as simple as mine. I think on SBL 9A you can place 100-127 or 37-47 compound gears with zero error in first case or 0.02 of 1% in second which is more accurate than mine. I can't place that gears on my SBL 80A. Capipio (17500)
Capipio, My gearing is as follows: Idler Gear is 80 tooth Quick Change Gear is 56 tooth And I can interchange the stud gear with either 40 or 20 tooth (normally 20 tooth for most threading). Dave (17520)
Metric threading
I am trying to thread a M10-1.5 draw bar. I have the 127/100 gear and can get the pitch correct, but am having trouble engaging the half-nut. When do you engage the half-nut to get the tool to track the thread. I have tried engaging at the same number on the thread dial but by the time I make 2-3 passes I have 2-3 treads. Is there some specific place you have to engage the half-nut? Gary (25133)
Gary: I believe with an Imperial Pitched Leadscrew no matter if you have the correct Imperial Gears to get the Metric Pitch of thread, once you engage the Split Nut you cannot disengage it or you will get multiple tracks. I think you must pull-out tool at the end of the cut and then reverse the lathe spindle to return to the start of the thread, stop spindle and reverse direction again and start your next pass all without disengagement of the Split Nut. I may be wrong as I have done little or no metric threading for about 20 years. Other members will chime in if this is not so. Ron (25134)
When threading metric, there is only one option: never disengage the half nuts if the lead screw is not metric. You have to reverse the spindle in order to come back to your original position. I have cut many metric threads on my lathe. It is the only way to go. I usually exert a variant of this: I disengage the split nuts at the end of the thread cut and then, stop the motor. Then, I reverse the spindle and re-engage the split nuts. Be careful when reversing the spindle. don't reverse when the lathe spindle is set to turn at high speed. What can happen is not pretty and scary. If you have a model A (9 or 10K) go on the South Bend Lathe Pix group and pick up my Excel spread sheet. Guy (25138)
It is also my understanding that, with a metric thread, the threading dial cannot be used. The safest way is to stop the lathe, back out the tool, reverse the lathe past the starting point to allow the lathe to take up backlash, put the tool back to the set point and adjust the compound, then run forward again. If you wish to experiment, put a dial indicator an the far end of the saddle, set at zero at the start of the cut. Note the EXACT line that the threading dial engages on. cut the thread. Disengage the halfnuts. Back out the tool. Come back to the zero mark on the dial gage. Put the tool back, adjust the compound. Engage the halfnuts at EXACTLY the same line. I believe this gets you where you want to go BUT I have never tried it on metric threads. Jim B (25142)
I've been taught by the old masters also that you have to keep the half-nuts engaged and reverse the motor for metric threading unless the lathe was designed specifically for metric threading. IIRC it has to do with the odd (127/100) gearing. Gene (25146)
If someone else mentioned this, I apologize for the redundancy. When threading, moving the cross slide can cause you to split threads. If you use the cross slide to retract your threading tool, you need to return it to the original position. Either zero the dial or use a travel stop. You can avoid all this by not touching the cross feed and using the compound to retract/advance the tool. Bill (25147)
Theoretically you don't have to keep the half nuts engaged when doing metric threads with a conversion gear. To keep the cuts in alignment you must, obviously, ensure that the relative longitudinal position of the tool and rotational position of the work is kept constant for each cut. If you had a bed stop arranged so that the longitudinal position of the saddle is always the same when you engage the half nuts and you always engage them when the chosen number on the dial corresponds to the same rotational position of the chuck you would pick up the threads perfectly. Might have to wait a long time between cuts tho' G Problem arises because metric threads themselves are irrational in terms of turns per unit length (needs a factor of pi to convert a pitch into turns per) and the 100/127 conversion is near enough irrational too. Proper metric workshop lathes usually have a fast reverse for the lead screw because, even with a metric screw, thread dials don't work very well. Either lots of odd spaced lines, multiple counting gears or both! Clive (25156)
You've over thought this one. Pi has nothing to do with this conversion. Pi is only a factor when converting from TPI or metric to DP or Modular threads. As a matter of interest, 355/113 is an almost perfect combination to generate pi, the error is 85 parts in 1 billion. As listed it's not a very useful value but 71/113 = pi/5 to the same degree of accuracy. While these are still odd values, at least they fall into a practical tooth count range. Anthony (25193)
DP and Metric Module Threads
Does anybody know if there are gearing charts available for cutting DP and metric module threads on SB or Boxford lathes? Anthony (24430)
This is an easy thing to calculate for the C. You need a compound conversion gear. (100/127 is common and exact there are others which are close). Now the Lead screw is an 8 tpi. This gives a pitch of 0.125". or 3.175 mm. Inserting the conversion compound gear results in the cross slide moving 2.5 mm for each turn of the headstock (for a 1:1 headstock to lead screw gear). You should have an existing 2:1/1:2 compound. Inserting this results in a 1.25 mm lead. The headstock gear is 24 tooth. If you wanted a 0.6 mm pitch then 24*1.25/0.6 = 50 Put a 50 tooth gear on the lead screw. Some pitches are not perfect Take 0.65mm 24*1.25/0.65 = 46.154 You can only have 46 teeth so you get 0.6522. This leads to a 0.3% error. Hope this helps. Note this is done from first principles. I have never cut a metric thread, but if I needed to and if I had a 127 tooth gear (I have a 100 tooth gear) this is how I would approach it. There have been several threads about how to come close without the 100/127 compound. Jim B (24433)
Threading Gurus (Metric)
I don't have metric gears on my 10L but need to cut a M16 x 1.5 right hand thread. Is there a standard thread that would be 'close enough'? Kevin (25006)
Depending on how close is 'close enough', 17 tpi is the nearest (it should be 16.933 tpi to be exactly 1.5 mm). If your lathe will cut this pitch you're lucky, my SB9"A doesn't so I worked out how to do it by hand filing a 27 tooth gear specially for this job. If you want, I'll try and remember/work out exactly how I did it. Nick (25010)
Kevin, I rough calculated that is would be a 5/8 (.625) diameter and 16.95 threads per inch or round up to 17 tpi. Don't know if the SB QC box does 17 tpi. It would also depend on what length of thread you need. A short distance 1-2 inches would be OK. 1 foot might cause problems. Also the class of thread needed. If you have 17 tpi on your QC box, then OK. Also you could get it close and chase the threads with a die or tap. Tom (25011)
The 1.5 part, by my calculations, which could be wrong, is very close to a 17 tpi. I calculate 16.92.This is one of the threads you have trouble getting to on a lathe. On my 9-C I would need a 51 tooth gear setting it up in a normal mode. I have a 104 and a 100 tooth gear. they could be used with a 2:1 compound. The 100 would come closest at 16.667. I don't think this is close enough to 16.92 to get you there. I could get the needed gear from Boston Gear but the cost would be more than a tap or die. The 16 part is 0.6304, not far from 0.625. So unless you can figure out how to make the 10-L, which I have little knowledge of cut a 17 tpi thread I think you need a tap/die. Jim B (25012)
As noted elsewhere, 17TPI is pretty close, less than 1/2 of 1% error. If this were a plain change lathe, I have some calculations at: http://lathe.com/tips/metric_thread_charts/1-5mm.htm Scott S. Logan (25013)
Kevin: I don't know what stud gear is in 10L but if yours is 48 teeth, placing a 34 teeth gear as stud gear, you can cut 1.5mm threads setting gear box at 12 TPI within 0.04 % of 1% error. Actually 1.49930556mm. If your stud gear isn't 48 teeth, you can figure out of this the stud gear to place. Capipio (25014)
Close enough is subjective. For grounding we would use a 3/8-16 female weld insert. If the unit went to Europe and needed a replacement bolt then a 10-1.5mm bolt would fit with a little effort and a ground would be maintained. The same is true for a 10-32 male stud and 5-.75mm nut also used in grounding. You can cut your threaded part 16tpi or 18 tpi and make it a little smaller or larger and use a metric matching fitting and see if that would be 'close enough'. JP (25017)
I have just look it up the following is what I have. On a QCGB Model A 26 = stud 80 = compound 56 = Box gear Will cut Metric screw pitch 1.50090909 Will cut TPI 16.9230769 David (25018)
I forgot to add= "place lever at B-4"(25019)
I have just look it up the following is what I have. On a QCGB Model A 26 = stud 80 = compound 56 = Box gear Will cut Metric screw pitch 1.50090909 Will cut TPI 16.9230769 What pitch do you select in the gearbox? Anthony (25024)
That would be with the gearbox set at 22 tpi? I used a setup with a 27 tooth stud gear, 40 tooth input to the gearbox and set that to 32 tpi, this gives 1.500187 mm pitch. This is slightly nearer, but whether the difference matters would depend on the application. Nick (25026)
I am glad to see that some people are using my spread sheet to calculate odd thread pitch/TPI. If someone has the part list and basic gear train info, it would be easy for me to do an equivalent spread sheet for the two different models of gear box for the heavy ten. For those that don't know where to find the Spread Sheet for the Model A SB 9 /10K, it is located on the south bend lathe pix group in the file section. I encourage everyone that have this machine to download the file and try it. With it, everybody can be a threading guru for the model A SB lathe. Guy (25056)
Actually, I worked it out from scratch. That spreadsheet is great, I wish I'd realized it was there. Nick (25071)

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