Think about what you will be making, for the most part say 80% of my work a couple of thou is good enough. I make a fair amount of stuff for old motorcycles and lawn mowers and only chase a thou or less if the part requires it say on a bearing fit. A little more care and the job is usually OK.

If you're not paying for your own time, then returning a machine to original specifications is not expensive. So far I've done a 1952 Hardinge HLV and a 19?? Beaver turret mill. 1976 Surface grinder will be done after I've re-lapped the surface table…

2 thou over 6 " unsupported is not to bad. On something a bit fussy you could most likely get that as good as spot on with a tailstock centre tweak the tailstock offset to correct error. Bed grinding place in the Nuneaton/Coventry area, most likely cost more than the lathe is worth. Bed grinding is just the start, you then have to refit the saddle and tailstock not to mention getting the workhead set up correct again.

Any clue as to what make and model lathe you have? Makes a difference to how easy or worthwhile it might be to fix it up.

Tapered turning with no tailstock centre is not always down to worn bed. Headstock bearings are a common culprit and should be fully sorted before any bed work is carried out. If its a Myford, for example, the bearings can be tightened up with the removal of a couple of simple shims, or a little bit of judicious scraping if need be. Headstock alignment can be adjusted with two screws on the headstock and either some shims or scraping on the mating surfaces.

Also, "levelling" the bed, or more accurately twisting it, can be used on some lathes, eg Myford, to get it to turn parallel. This can be used as a dodge to compensate for worn bed.

Also on the earlier pre-1970s or so Myford you can do the "wide guide" conversion to abandon using the front vertical shear as the guide and put a strip of guage plate in the rear of the carriage to bear on the rear vertical shear of the rear bed way which is unused and still straight. This conversion has been covered in ME and MEW many times over the years, IIRC most recently in a recent (last few months) MEW article on refurbing a Myford.

Another cause can be bell mouthed chuck jaws, which can be reground with a toolpost mounted Dremel tool and the correct "cloverleaf" packing ring between the jaws.

Bed regrinding is a last resort, not starting point, for getting old machines to turn true.

Edited By Hopper on 24/04/2017 01:24:20

Ditto, not familair with a Lang lathe. Some pics would be nice, so we can see what we are talking about.

That said, yes .003" movement at the headstock spindle is at least .0025" too much. More like about .003" too much. There is absolutely no point at all in proceeding any further with alignment etc until you have fixed the headstock bearings. This amount of slack would be enough to create the taper on your test turning piece. So you may not have a bed wear or bed alignment problem at all, just a headstock bearing adjustment problem.

Depends on what the shims are like, but usually you can cut out new shims from shim stock and insert them in place of the old ones. How thick are we talking about? If they are big enough, you might be able to very carefully file them down, using a mike to make sure they come down parallel. Or you may be able to rub them on emery cloth on a sheet of glass to knock a few thou off. It does not take much to remove the .003" you seem to require.

EDIT: PS just had a squiz at Lang Junior on the lathes.co.uk site. It looks like if you have the roller bearings, there would be a large circular shim that goes under the collar that provides bearing pre-load? You should be able to cut a new one out of shim stock that is a bit thinner than the original and try it out?

The website also indicates you have a very good quality machine there "better than Dean Smith and Grace and many German machines" is pretty high praise. So well worth persevering with, cautiously so as to not overdo things.

I'm not a big fan of spending money on ground test bars. You can turn one up yourself between centres if you sort out that headstock bearings and then the tailstock alignment. But even then, final adjustment is best done by turnin a 6" long piece of bar as you have done. This gives you the "real world" reading of how the lathe is cutting, which takes into account wear in the carriage and cross slide etc and the forces on them under cutting load. Static alignment is one thing, working alignment another.

It seems unlikely that a carriage crashing into the headstock would budge it on a solid machine like this. I woiuld not worry about that possibility too much.

You need to measure the length and the diameter at each end of the headstock spindle taper. It may not be Morse, but some odball like Brown and Sharpe or Jarno or a couple of others that used to get used. Or it could be a Morse 5-1/2 which is a MT5 but only half the usual length.

Edited By Hopper on 24/04/2017 09:23:06

An impressive and extremely heavy duty lathe for there size. Anythings possible of course, but after seeing those pictures from KWIL's link (thank you) I'd be even less concerned about that crash shifting the headstock just as Hopper said. And I think much the same as he does about spending the money on those test bars. First they have to be made very well with as close to zero runout as possible. Getting that accuracy no matter where there made costs a great deal of money.Then the spindle taper has to be in perfect condition or the tests don't mean much. I have some and have learned that for what they cost the return wasn't worth it. They are handy for checking and aligning a tailstock not so much for a true C/L with the headstock, but for the tailstock being angled off side to side or pointing up or down hill. But even that can be done without having one.

Your Lang lathe certainly has the quality to justify a proper rebuild. If you ever decide to do so it's best not to chose to have the grinding done by price alone. The shops that do know what it takes to correctly align and regrind a lathe bed will charge accordingly. As Hopper said sorting out your headstock bearing clearance should be the next step. With that .003" clearance it's impossible to judge how much the bed wear is causing a taper in the workpiece and how much the excessive bearing clearance is. Logic and some guessing suggests it could be causing most of that .002" taper. It is a very heavily built lathe, but even so it's not impossible for the bed to twist and on an uneven floor, even more so if it's been bolted down without being sure it's level or not twisted in all directions. That could have happened at any time before you bought it. The lathe carriage then wears to the beds position and the bed can also take on a permanent twist over time. If so it needs to be shimmed and gently forced back into to being true.

To post a photo, you need to go to the top green line, and click on Albums. Reduce your photo to about 640 X 480, and use jpeg image. you then can transfer the image onto your thread by clicking on the little camera in the top row of the message box.

Ian S C

The .003" of play you said you have in the headstock bearings would cause it to turn smaller toward the chuck, larger toward the tailstock end of the job. You need to get rid of that play in the headstock spindle bearings before you can make any meaningful observations about what might be happening with the bed and carriage side of things.

You would have to be taking a pretty aggressive cut to put 200lbf through a tooltip.

Neil

Center drill a steel or aluminum bar of whatever you have around. A couple of inches in diameter and 8"-12" long would work well. Center drill each end.Then take a lump of any steel you have handy 1"-2" in diameter and roughly 2" long. Turn half the length down by around 1/4" smaller in diameter and do a good facing job where that step is. Reverse that in the chuck jaws and turn a 60 degree point on it. (30 degrees per side as a normal fixed center would have) Now DO NOT remove that from the chuck until the next test is complete since the center tip is now as concentric as the lathes bearings will allow. That turned step goes against the face of the chuck jaws and prevents it from being pushed back in the chuck. Set your previously center drilled bar up between that headstock center and the tailstock center. Add a drive dog at the headstock end and let one of the chucks jaws drive it.Turn the length of the bar until it fully cleans up and measure each end with a good micrometer. This removes any chuck jaw holding inaccuracy and will produce a proper example of what the lathe can actualy do under cutting conditions. But only if your tailstocks side to side alignment is properly set to the headstocks center line.

You have to eliminate as many variables as possible or cutting tests are meaningless. As each part of the lathe is tested and verified as correct that's one less variable you can eliminate. By doing the proper tests you can then access exactly where and what any problems might be. Turning between centers is the most accurate way of holding and turning any shaft type work as long as it's diameter is large enough to prevent bending. As a bonus it allows work to be turned end for end put back in the lathe and still be accurately centered. If the tailstock is properly aligned and your turned test bar has less than the .003" taper your seeing then the faults lie elsewhere.

Given the age of your lathe I'd expect your tailstock is worn especially at the front where it slides on the ways. However it takes a great deal of wear to show very much change on the parts diameter. George Thomas and a few others have clearly showed that by simple math.