Jim Reed wrote:

I just got the first 3 jaw chuck for my lathe. I was using a 4 jaw for the
last two years. It just got tiring trying to true up the work and not mar
it in the process. I never did get too good at it.
I put the 3 jaw on the lathe, checked the body for runout, and it did not
register any error on the dial indicator. Chucked up a 1.75" dia. piece of
steel, and made a light cut on it. It measured .001 runout after the cut.
Probably due to rough surface finish.
Then turned this piece around and chucked it in the 3 jaw, using the cut
surface as the holding location. When I measured the runout (still using
the cut surface to measure), I was indicating .020 out. I tried this
several times and it varied from .005 to .020. I found some rust on the
inside of the jaws I thought might be causing the problem, but removing it
didn't seem to help.
My lathe is a Reed-Prentice 16X54, the chuck a Skinner 8.5" 3 jaw I just
pruchased on Ebay. The chuck has an integral L01 spindle mount, and it
looks like it has sat and gotten a little rusty for most of its life.
Any constructive suggestions would be appreciated.



..005" runout isn't too bad for an 8-1/2" 3-jaw. .003" is about as good as you
can expect even from a very expensive new chuck. However, there are some things
you can do. The first thing is to completely disassemble your chuck, and clean
it using solvent & compressed air. It's amazing how a tiny chip somewhere can
bollux things up. When you put it back together, pay close attention to the fit
between the scroll and the central boss. Any clearance there translates to
runout in the jaws. Older chucks can accumulate wear there. If it is worn then
chances are it is worn uniformly, so you can cut a suitable shim that fits all
around the central boss, like a wedding ring. Give it a little lubrication in
the back where the pinions go, and leave the jaws dry and clean, and reassemble
and test. When you test, shoot for a good finish. Pay close attention to how
your piece is oriented in the jaws (maybe mark it where the piece touches the
no. 1 jaw) and replace it exactly, and tighten it from the same pinion, and I'm
guessing a lot of your error will be gone.

Even with .020" error a 3-jaw is completely usable for many things and a highly
desirable addition to your lathe tooling. Many things can be turned entirely in
one setting.

GWE