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