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Setting tailstock height on a used/worn lathe?

APD

Stainless
Joined
Nov 5, 2005
Location
Hudson Valley, NY
Anyone got a good technique for measuring/setting the tailstock center height?

Right now my TS is too low when workng near the spindle. I assume this is because of bed wear....but I dont know if the height is correct when the TS is way back on the right side of the bed? How do I measure the height of the TS when it is all the way to right? What do I use for a reference surface?
I realize I probably cant get the height perfect for use on every part of the bed, but I would like to measure things so that I could determine an 'average' height that will be 'good enough' for most work.
 
Get a length of ground round shafting (MSC ?), perhaps 24" long, and drill center holes in each end.

Then, mount between centers.

Finally, place a DTI in your lantern or QCTP toolholder (the Starret DTI set includes a mounting bar which fits a lantern style perfectly), and run the length of the shafting in both X and Y, noting any deviations.
 
peterh5322,

Does your process assume having a second lathe on hand with the tailstock known to be on center with the spindle to produce the required test bar? Otherwise, what would be gained by "center drilling" with a TS suspected to be off center.
 
Common misconception, even if the centerdrill
is in a tailstock that is low, high, too far
front or back, it will still produce a hole
in the stock that is concentric with the
axis of the spindle.

Won't be a *pretty* hole, but it will do for
the test described.

A better way would be to put a test indicator
in the spindle, and sweep the inside of the
tailstock ram. That gives the numbers for
the tailstock near the headstock.

Next move the tailstock to the right, and put
a piece of stock in the spindle, so you can
attach the indicator at the end of the stock
and again sweep the ram. It'll be much less
rigid but it's not a bad first pass, and could
be correlated with the test bar mentioned above.

Jim
 
If you want to center-drill a piece of stock, chuck it and center as best you can with an indicator. Keep the face of the workpiece even with the front of the chuck jaws.

Bring the tailstock up and drill with a good centerdrill. Your hole will be concentric with the axis of rotation of the spindle unconditionally. If your tailstock is not properly aligned, the hole will be larger than the centerdrill pilot, but it will be centered on the workpiece axis if you indicated it in properly.

If the tailstock is way out of alignment, you might have a problem with the centerdrill dragging on the workpiece rather than cutting. Try to determine the point of contact and rotate the centerdrill so its cutting flute intersects that high point, which will be located at the point of maximum error of the tailstock from the spindle axis.
 
Just to put it out there: you don't need to indicate the bore of the TS. You can indicate the outside of the ram if that's easier. Make the indicator zero on each side of the ram ( thus proving the ram is centered left/right). Then indicate the top of the spindle (you can't do the bottom b/c of the keyway). This gives you the height deviation of the TS ram. Correlating this with an indication on the actualy TS taper can give you a chance of at least partially compensating for flex of the indicating apparatus during measurement. I did this on my 10L during the rebuild, and it worked great. The interapid indicator was especially good, since it had the flexible mounting arm which facilitaed easy repositioning.
 
The quick and dirty way to see is your tailstock base is worn is to turn it upside down and the wear will be evident at least on the flat side by the diference between the surface that slides on the flat lathe way and the overhang area that gets no wear. I did this on a tailstock of a heavy 10 and found a wear of .012" on the front and .oo8 on the rear. That is tilted. So shimming with precision shims will not correct everything.
Several years ago SB wanted $ 300 for a new base and even then it might need maching or shimming to match your lathe.
Since the base is just a rectangular chunk of CI with a lump in the middle I elected to buy a piece of continuous cast iron and machine a new one. This stuff is a dream to machine. I am curently blueing and scraping to fit to the V match.
A cheaper way is to remachine your worn one, blue, scrape and shim.
Walt
 
Here is one way to check (not a SBL, but the idea still applies). This is a short 2" piece of black pipe with a 1/4" dowel pin welded to it for a mount for the DTI. The chucking of the pipe is not required to be accurate, just that it doesn't slip.

One can also sweep the ID of the bore, perhaps a better test.

10EE_Test_01_small.JPG
 
Don't forget, Matt's idea can be extended by,
err, extending the piece of stock in the chuck.

The reason I suggested sweeping the *inside* of
the ram, is that on high mileage machines you
have no idea what's been done to the bore over
the years. It may well have been reamed many
times so it's off center. It's worth checking
both to get some idea of the issues involved.

And this is, apparently, a high mileage machine.

Jim
 
Bring the tailstock up and drill with a good centerdrill. Your hole will be concentric with the axis of rotation of the spindle unconditionally. If your tailstock is not properly aligned, the hole will be larger than the centerdrill pilot, but it will be centered on the workpiece axis if you indicated it in properly.

Common misconception, even if the centerdrill
is in a tailstock that is low, high, too far
front or back, it will still produce a hole
in the stock that is concentric with the
axis of the spindle.

Won't be a *pretty* hole, but it will do for
the test described.
Jim

I am now having this problem with the Lodge and Shipley lathe I am running at work and could never figured out why the center drills were leaving a nipple in the middle and boring a hole rather than drilling a hole. Also the center holes are coming out bigger in size than the drill itself. Two tool and die makers at work told me to check it out when I have time, since the one guy checked how level the bed was and it's level within a few thousands he said. I put 2" diameter x 19" long turned bar in the 4 jaw chuck and indicated/tapped in the whole length of the bar to run true with the spindle. (Now I know this is not necessary). I then put the magnetic base on the end of the bar and swept the inside of the tailstock ram bore with the indicator and the needle moved approx. 0.050", meaning the tailstock is low 0.025". That explains why everytime I loosen the steady rest, the bar picks up off the rollers about 0.025", after the rollers are set to the tailstock live center height. It also explains why the jaws have been making creeking noises, because the jaws are fighting the live center/steady rest.

The supervisor said I must be wrong somewhere because they never had a problem with parts, but that is because even though the center drill is low, it is still boring a hole concentric with the shaft, just a larger center hole. Who knows how far off from 60 degrees it is though. It has the same effect as if a steady rest is set too far off center when a center hole is drilled.
 
Just to put it out there: you don't need to indicate the bore of the TS. You can indicate the outside of the ram if that's easier. Make the indicator zero on each side of the ram ( thus proving the ram is centered left/right). Then indicate the top of the spindle (you can't do the bottom b/c of the keyway). This gives you the height deviation of the TS ram. Correlating this with an indication on the actualy TS taper can give you a chance of at least partially compensating for flex of the indicating apparatus during measurement. I did this on my 10L during the rebuild, and it worked great. The interapid indicator was especially good, since it had the flexible mounting arm which facilitaed easy repositioning.

I agree with this method, with the following caveat: center the tailstock sideways at the same time. This way you will be able to tell where the zero indicator reading should be in the middle of the keyway slot on the bottom of the tailstock ram. Make sure that you have the ram clamp engaged when making this test.

Lord Byron
 
With this tailstock sitting 0.025" below center, I guess I am still able to face something square to the shaft axis when running on the tailstock live center or steady rest?
 
yeah I have to take it really easy when center drilling and it rounds the tips of the center drills right away, I let maintainance know about it and that it needs shimmed.

The one guy I was talking to at work, thinks that with the shaft being held down 0.025" too low by the steady rest, that the center hole will be drilled in the shaft at an angle. However, I don't think this is true because the center drill is acting as a boring tool, and the shaft is running true at the chuck and at the steady rest, so I think the center hole will still be concentric to the shaft, it will just be bigger in diameter than the center drill itself.
 
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