Lathe - Turning - Accuracy/Runout



Checking runout (May 9, 2004) SB-9A setup accuracy (Oct 26, 2004)
Possible runout 9"C  (May 27, 2004) How to get an absolute center? (Mar 2, 2005)
Accuracy determination (Jul 27, 2004) Accuracy?/ Runout (Mar 4, 2005)
Checking runout
I was the lucky soul who won the S.B. 9" that sold on eBay a couple of weeks ago for $360. How does one check the spindle for run out? Also what else should I check for wear? (18959)
Runout is built into (or out of, as the case may be) the spindle. I think the question(s) you need to ask is/are: How do I check for play in the headstock/spindle assembly? How do I check for twist in the bed? How do I check to see if the tailstock is aligned to the headstock? And if you have a scroll chuck; "How do I check the chuck for runout?" If you don't have a copy of "How to run a lathe" HTRAL You should get one. You should also check the archives on the first three subjects above. There has been a lot of discussion recently on all three. Perhaps the easiest thing is to make sure you lathe is not twisted (leveling) and then cut a test piece of rod, first at the chuck/collet and then some distance away from the chuck/collet to see if there is a taper and then go on from there. But check the archives and the FAQ's first. Jim B. (18964)
Grant here from new Zealand seeking backing plate for sb lathe chuck will be getting Chinese chuck to replace worn one which will be placed on wooden ball turning lathe Chuck is 5 inches I think The motor on the lathe blew up in huge shower of sparks and have placed another old one but does not have reverse for screw cutting oh I though I was dead for a few seconds all was dark and quiet as all lights went out as it was night soon to make a milling attachment for lathe and are currently making a 4 axis milling machine for router so I can make complex parts of plastic and wood and should get away with aluminum I build wimshurst and voss electrostatic generators at a very high standard and hope to sell them in the USA which will be the biggest market But have sold three here in a city of 250.000 people And may sell more hope someone can help as this old chuck can be a pain in the arse. Grant (18967)
Grant, I'm in NZ as well and a backing plate solution (the one I use) is to get a blank cast and turn it up yourself (good machining exercise). If your in the sticks it may not be so easy but most main centers would have a foundry. Dave (18968)
Dave Grant here and I live in christchurch new Zealand and I think I know some one who can make me a backing plate just have to get similar sized chuck first What part of NZ are you in? I build all kinds of machines sheet metal benders and are currently making a 4 axis milling machine which uses a router and will be used to make plastic parts as well as wood will be a lot of fun And also have large power hacksaw in the pipe line have major parts I also make wimshurst and voss machines to a very high standard and have a voss machine on display at the arts center in church I hope to sell these after I get web page made up. Grant (19011)
Grant I'm in the Wellington bit of NZ and it looks like you're into doing some interesting things. On the subject of your backplate one idea is to get the someone you know to do the thread and then finish it yourself with the new backplate screwed onto your own spindle thread - gets everything spot-on for your own lathe. My last big project was rebuilding my 1947 Southbend Heavy Ten lathe (great bit of machinery I must say) - that kept me out of mischief for a few months! Dave (19017)
Possible runout 9"C
I have a 9" SB lathe model C, that I am setting up. I have mounted the two chucks, one at a time, and put the tool post against the chucks and I seems that both have a slight runout. (I turned it by hand). The chucks are of the threaded type. My spindle has a thin flange (1mm) at the chuck. It seems that this flange is a part of the spindle. It is also bent a little. I wonder if there is gonna be a part (like a thick washer or something) put on the spindle before the chuck is mounted. If so it is missing on mine. Now the chucks are only against the threads. Could it be that the chuck should be seated against a shoulder, because on mine it is not? I haven't seen a detailed drawing of the headstock of the 9C model. Are the types 9A, 9B, 9C and 10K all different lathes and headstocks? If the spindle is bent, can it be saved or can i just scrap the whole lathe? Or should I get a new spindle. I guess a new spindle is very expensive. I have had the spindle out and both the spindle and bearings looked like new. Torfinn (19321)
That is the register of the spindle. Which way is it bent? Back towards the headstock or towards the threads? The chucks/faceplates bear against it so you have a consistent bearing on the threaded spindle. the chuck should bear against the shoulder. Make sure your threads on the spindle and in the chuck are CLEAN! look in the files section for thread chaser. no they are all 9" are the same. 10K is very similar. It is unlikely that it is bent. Check your spindle for run out. remove chuck and check with dial indicator. Also check to make sure that the bearings are adjusted properly. Instructions in the files section. dennis (19322)
Torfinn, here is a link to download a copy of the US army manual for the 9" lathe. Winston http://www.metalworking.com/dropbox/_2001_retired_files/sbarmylathe.pdf (19366)
Accuracy determination
I have a 9A SB with a 42" bed that I would like to evaluate. Is there an algorithmic approach to this? What I'm asking is how should I proceed? Is it appropriate to turn stock, in a chuck? between centers? If so how are the results interpreted? How can a dial indicator be used? Is there some way to use a test bar (12"X 1") that I know to be true and that is center drilled? (It's a factory new hardened shaft from a printing press.) I realize that this is a complex issue as there are many variables involved but I was wondering if there was an accepted "scientific" approach. Bob (20229)
All that you are asking is explained in South Bends book "How to run a lathe". They are available on Ebay. Paul (20232)
In addition to taking a look at "How to run a lathe", you might also want to take a look at http://www.cartertools.com/tgtest.html It's a little more narrative than HTRAL. Paul (20233)
Machine Tool reconditioning Chap 26 has a very good description on method to use in order to align a lathe and the use of test bars. Guy (20251)
SB-9A setup accuracy
I just acquired a 9A (model NAR) from my Dad. Shipped from NH to WA... ouch. The lathe is in pretty good shape aside from some cosmetic oxidation (rust :^( and some slight wear in the ways near the headstock. The hand-scraping marks are nearly, to completely, worn away there, but there's no evidence of excessive wear. When I run the carriage from head to tail with the lock barely loose, I get some starting about 1/2 way down the ways, but it's not much - a couple of extra ounces of effort? In any case, I've got it set up now according to HTRAL - concrete studs in floor and bench firmly attached to said studs. Lathe firmly attached to bench. The problem I have is that when I accurately level both ends of the lathe bed (precision level) to within .0002 per 10" (well within the tolerance HTRAL suggests of .003 / 12") I find that with a test cut, I get a taper of nearly .002" dia. in 3.5" (on a piece of 1" stock). I first suspected the 3-jaw (which I'm now sure needs fixing, separate subject) so I switched to testing on a piece of .5" steel in a collet and added a carefully centered dead center on the tailstock. The taper for that cut was reduced, but only to about .001" dia. in 3". Then, remembering that in order to level the bench, I had to pull two diagonally opposing corners down, sort-of flexing the table, I released one of the top-holddown nuts and let back tailstock corner come up. The tailstock end is now so out-of-level that it exceeds the range of the precision level - so, more than .0015" in 10". When I redid the test cut with this setup, the taper was reduced to .0002" in 3" - better, but not good enough yet. Before I go reefing that tail end even higher, I thought I'd ask some advice. Something seems to be out-of-whack here and I don't understand it. If the bench is bent, then having to pull it down with the top nuts until level should be fine, but doing that appears to INDUCE taper rather than relieve it. Does anyone have any idea what could be wrong here? headstock mis-alignment? excessive bed wear? Jupiter is too close? Should I continue to raise that back corner until I get a straight cut, or look for problems elsewhere? (21553)
Try this way. 1) Do not fasten the tailstock end bolts on the lathe bed.. 2) Now with the headstock end secured to the table level the table on both ends. 3) Place the level on the head stock end of the ways. Be sure that they are smooth and flat. Keep it near the head stock there is less chance that the ways have been worn or damaged. The ways may or may not be level. Note where the bubble goes. 4) Move the level to the tailstock end. Shim the end, being sure to tighten the bolts after each change until the bubble is at the same spot. The object its to remove the twist from the ways. 5) Make sure the tailstock is centered, both left and right and up and down. Use an indicator in a collet in the spindle. Now try cutting a bar and measuring the taper. Jim B. (21563)
Keep adding shims till the lathe turns and bores straight . The bench is not very flat I have seen many like that. Boris (21565)
The important part is an accurate cut. The level will get you close and the test cut is the final determining factor. When measuring with a level you may not be touching on the same location as the cross slide. Southbend has always been a reliable machine so having to 'jack down' a corner in the leveling process is an indication that something may be wrong and its usually 'operator error'. JP (21572)
Hugh, There is no headstock alignment 'per say' but there is spindle play you can check. Also check the center height of the tailstock in relation to the spindle. JP (21573)
I did check the alignment of centers and they were as close to matched as I could tell visually. I also indicated the inside of the spindle against the bed and couldn't detect any motion on the dial (a LastWord - resolution to .001"). As I said in a previous message - it appears that some over-enthusiastic tightening of the lathe to the bench may be part of the problem - it was causing a "bow" in the front rail when both ends were as close to level as I could measure. Relieving the bed to bench bolts a little removed that. I'm about to see if I can now get everything tight again without those distortions, and then I'll try another test cut. (21579)
In my initial setup, I apparently I failed :) I re-ran the setup along the lines you suggested - got the headstock end leveled, then the tailstock end (had to repeat because torquing one end slightly changed the other). So, I ended up with both head and tail ends at as precise a level as I can get. I indicated from the bed to the inside of the headstock taper and found essentially no wobble, so the headstock bearings appear to be ok. Doesn't say anything about alignment, though... I then tried the level near the middle of the ways... and found that it wasn't level! I released the bolts holding the lathe to the bench at the tailstock end, and things settled down - now there's an I'll play with it some more tomorrow, and as suggested by Boris, I'll try shimming the tailstock end between the bench and the lathe itself - first to get no twist, then to get a straight cut. BTW - just HOW straight should I expect? I've not worked in a toolroom, just on this lathe as a kid. I taper down to about 1 thou per foot (assuming my measuring was up to snuff), but that seems excessive to me. I'd like to see less than half of that. (21580)
You may want to remove the top slide and place the level on the cross slide. Then move the saddle up and down the bed. There should, of course be no bubble movement. Also be sure and check that tailstock with a dial indicator for both horizontal and vertical alignment. Ed P (21582)
.001/ft is pretty decent for a lathe with noticeable bed wear, IMHO. Lurch (21583)
The bench is likely to be the main cause of the problem - it's of heavy sheet metal construction (like 18 or 16 ga. steel). I ended up shimming the back of the tailstock end by about 6 thou or so, then re-leveling. I did several iterations because every time I tried re-tightening the lathe to bench bolts, it would put that upward "bow" in the front of the bed. With 4 pieces of shim stock, that finally stopped. I now show something like .0004" of taper over 4" from head to tail (assuming my measuring was up to snuff :). That seemed acceptable for now. If I have to cut any 24" long acme screws, I'll probably have to revisit it. Anyway - thanks for the suggestions - it got me on the right track! (21585)
I see now - although I have an issue with the lathe to bench clamping. The bed really IS pretty much without wear - my Dad bought this new and hasn't really put much time on it. Can still see traces of the flaking over the entire ways, although from 6" to 1' from the headstock it's nearly worn off - but that's what.. a tenth, maybe? less? Good idea on putting the level on the cross slide, though! I will try that and see how it looks now. (21587)
I think you should look at the effect of your drive belt tension as a possible cause of twisting on the bed. Like all machine tools originally designed for overhead lineshaft drives, the belt tension was usually vertical, countered by anchoring the m/c to the floor. The typical belt driven bench lathe requires a rigid base between the headstock support and the drive/idler pulley arrangement to contain the twisting effect on the bed caused by the belt tension. The tailstock base is less important unless it is the most secure of the two supports, in which case it can increase the twisting effect on the base. A good lathe foundation is always worth the trouble it takes and will minimize mysterious tool chatter. Jim (21797)
I'm in the process of re-setting up shop in the new location. any opinions on how about two pillars of concrete block mortared together and filled with concrete for a lathe stand? Lurch (21814)
How to get an absolute center?
Can anyone tell me how you get an absolute center in an existing shaft? I've tried setting up with a 4 jaw and 3 arm steady and boring with the compound set at 30deg and then using a spotting drill in the resultant hole, I still get 5 tenths tir. Bernard R (25694)
Bernard: Tooling the center with a high speed tool should get it. Is job running absolutely true in steady? Check runout of center after tooling with high speed while still in steady. Is it .000? Does it runout .0005 when you put it on the live center? Do not use spotting drill after high speed tooling as it is unnecessary and you are only reintroducing any tailstock center height error. Ron (25695)
Bob, I think the problem I had was that there was a tiny pip after I'd bored the center, I examined another trial bar. I think I have to drill a small hole first then machine the taper, that way even if the first hole is off the taper should be OK. Yes, I did check runout before and after boring. Bernard R (25696)
Bernard: Drill a center with center drill first and then tool that hole with a high speed tool. Ron (25697)
Always use a center-drill to start with. They come in numbered sizes in case you haven't run into them, #1, #2, etc. It is the same as drilling a small hole first. Then if you need to re-tool, (the term we use in the shop) the center, there won't be a small pip on the inside. You need to be able to get this right. Most of the time center drilling isn't terribly important, but it can mean everything. Bernard R (25731)
Accuracy?/ Runout
I have just finished cleaning my new to me 1967 south bend model A 9" lathe and am back for some more good advice. My question is, I have spent the last week taking measurements for runout with my brown and sharp test indicator. I am getting: Spindle taper: .000125 3 jaw: with a piece of 7/8" dia steel: .00075 with a piece of 1 5/8" dia steel: .00225 How do these compare with others 9" model A and about what kind of accuracy should I expect with this lathe. Also could someone please explain to me how accurate .0005 of tolerance is, I have never gotten a direct answer. zkling3 (25750)
It's a 1/2 a thousand that is so close a small nat scuarched, couldn't get through. If it where +/ - .0005 That would be .001. Duane (25752)
Cigarette paper is .001 Take out your old snake skinner and slice the paper down the middle and you have .0005 I grind +/- .0002 and can turn Pretty close to the same on my 1942 9" SB. Bruce (25762)
To get a feel for what you're asking take an old ball bearing and first turn a shaft for it. For a push fit the shaft should be (- .00015 -.00035/inch), for a sliding fit those numbers would be (- .003 -.00045/inch); say your bearing has an inner race diameter of 0.5", a push fit shaft would be (.5 -.00015 -.000175 = .49967") for the sliding fit it would be (.5 -.0003 -.00025 = .49945"). When you've done the shaft then do the housing for the outer ring. Bernard R (25763)

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