Slight taper turning between centers

Only had 20 minutes today, but I think it may be bed/tailstock wear.

Long story short, I went to re-check the run-out of the live center before swapping in the dead center (I do have one), but my carriage wouldn't clear my tailstock to check run-out on the live center. The 0.004" of runout I measured the other day was on the collar of the test bar. I normally have the ram ~1/2" out from the tailstock, so to get clearance to check the center itself, I backed up the tailstock so the ram was out 1-5/8", and the tailstock was now back 1-1/8" on the bed from where it was before.

In the new position I saw < 0.001" of run-out on both the live center itself and the tailstock side collar of the alignment bar, and the tailstock was ~0.005" offset towards me. I re-adjusted the tailstock alignment, and now have < 0.001" of run-out on the live center and tailstock collar of the alignment bar, zero (or not measurable) run-out on the headstock collar of the alignment bar, and what looks like an aligned tailstock.

Bed wear or tailstock/ram wear?

I'll try taking some cuts as well as throwing my dial indicator on the headstock as Mike suggested in the morning...
 
Technical Ted said:
How level is your lathe? What did you use to level it?

Ted
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My lathe is close to level with a machinists level. I say close because the bench is level, and while I did level the lathe before, my bench is made of wood, and the level can change based on how hard I tighten it down.

I thought this is more of an issue with newer lathes?
 
All lathes must have no twist aka level.
 
I had a thread on tailstock adjustment on the Richard King forum here a few days ago. Might be of some help. Dave
 
Your 0.022" is far outside what a bed twist would give you. You might be suffering from tailstock spindle droop, a common SB problem.
 
Plus if it was twist it would be over the entire length.
If it was a low TS the piece would be larger on the TS end not the HS end I think.
 
brandon428 said:
My lathe is close to level with a machinists level. I say close because the bench is level, and while I did level the lathe before, my bench is made of wood, and the level can change based on how hard I tighten it down.

I thought this is more of an issue with newer lathes?
Click to expand...
The only reason you level lathes is to remove bed twist. A level does not need to be level to cut true.... but, there must be no bed twist. Bed twist, depending on how it is twisted, can cause all kinds of tapers. See if this South Bend document helps.


Ted
 
SLK001 said:
Your 0.022" is far outside what a bed twist would give you. You might be suffering from tailstock spindle droop, a common SB problem.
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How is that remedied?
 
Have to confirm first. With both dead centers in, bring the tailstock up to the spindle snug the hold down and see whether the two tips touch correctly in the vertical. Next start extending the ram and see whether the tips still touch. The worst should be a maximum extension. Also tighten the lock for the ram and see what happens then. Many times the ram will shift as the lock is tightened.
Once we have the data, we can figure out what to do. The usual fix is to bore the first inch or so, to fit a bushing to support the ram. Once the bushing is in place here comes the slightly hard part, ream that bushing to fit the ram and inline with the spindle. Milling machine and reamer with proper fixture.
Or attempt to find a better tailstock, $$$$ and they not commonly found anymore.
Pierre
 
Ulma Doctor said:
you can easily make a dead center in the headstock, the tailstock needs one to rule out alignment issues
your spindle bearings may be loose
to check, mount a dial indicator on top of the spindle- insert a suitable rod larger than 5/8" and about 20" long into the spindle
give a pull up and give a push down- observe the dial indicator readings and record
Click to expand...
I get .001” of vertical play. Is that considered loose?
 
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