Just the obvious, make certain the cam pins rotate the correct amount and
the new back plate and spindle are spotlessly clean. take a light test cut
on the backing plate, release and remount. Make certain that the backing
plate mounts true consistently. Then and only then machine to size.
Steve

wrote in message
...
I bought a used 13 X 40 Jet lathe a few weeks ago. When I bought it
I knew the 3 jaw chuck didn’t run true but the price was right. The
chuck it self hold true to less the 1 mil TIR but anything chucked up
wobbles about 20 mill. This chuck has the replaceable jaws and is a
D4 mount. The annoyance level has reached critical values so I am
going to fix it.

Does anyone have some ideas on how to fix this?

I bought a new plain back chuck and a back plate. Any lesions
learned machining the back plate?

Thanks