Lathe always turns a taper with a live center

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taiwanluthiers

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My lathe is a bit weird.

I've leveled the ways, aligned the headstock, aligned the tail, etc.

Then when I drill a center, then pull the stock out, and use a live center to support the end, there is ALWAYS a 0.1mm taper. It does not seem to matter how short or long the stock is, but I always have to correct the tail stock to remove the 0.1mm taper, but yet if I use that same setting to drill a center hole it's off center by exactly 0.1mm or thereabouts.

What could cause this? Could it be the live center?
 
It sure sounds like your tail stock or one of the centers is off center by .05mm.

Did you check it both horizontally and vertically?

How did you go about aligning it?
 
I align the head by turning something unsupported, and adjust until it no longer tapers. However for some reason when I go to align the tail stock it is always off by around 0.1mm
 
My guess is that the tailstock is twisted. When using the center, it is relatively close to the tailstock compared to a drill mounted in a chuck, If you adjust the tailstock to be dead on for a center and there is a twist, a drill would not be on center. You may be able to assess this by extending the quill and sweeping it with a test indicator.
 
How can you correct a twisted tailstock?

Actually, the tail stock becomes really hard to turn when I try to extend it beyond 2 inches.
 
My tailstock had a "twist". I found that there was some play in the side to side adjustment. I was able to turn it straight and tighten it down. I no longer offset it to make tapers. I built a taper attachment for tapers. Now I need to make a longer one for when I need to make a very long tapered part.
Also check for vertical offset in the tailstock.
 
Does the center have runout? Sometimes pressure is enough to push the center if it has runout and the part is larger on the center end. Dave
 
I think what RJ was saying is that your tailstock may be slightly rotated around the Y axis. It's a common problem for lower end lathes, but usually can be addressed with shims between the tailstock base and top. The vertical boss on the base may be off, or the mating surface on the top part may be off. Sticking the right shim between those two surfaces should do it.

Just follow RJ's coments on how to evaluate the rotation and go at it with the shims.

A tailstock can have several problems all at once. It can have nod, where it's tilted up or down. It can be shifted forward or back on the X axis. That is a design feature that can be used to turn a desired taper, but it usually is not correctly adjusted at the factory for straight turning. It may not be at the right height (they rarely are). And it can have the rotation problem.

When I first got my lathe the tailstock was so badly misaligned that I broke the tip off one of my center drills when I tried to use it on a steel rod (!). I eventually got it all sorted out so it's likely you can, too.

The tailstock on this class of lathes is commonly viewed as one of the most poorly-made attachments they come with. So it's no surprise that you're finding it necessary to work on it.
 
I can see a nod with the tailstock.

The problem is if I try to correct it with a shim, it makes the entire tailstock too high, it means I would have to mill the entire tail stock down by about 1mm in order to bring it to the correct height. I can find the nod just by simply chucking a long drill bit to it.

I do not know how to correct it, but I do need to shim the front of the tailstock by about 1mm in order to correct the nod, however doing this would make center drilling impossible.
 
Are parts available for your lathe? Have you considered finding a replacement tailstock?

What do you have? Photos, photos! We like photos!
 
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