I have a 8" 3 jaw chuck that I got with my Sheldon. It is rusted and I
cannot see any marking on it anywhere. I also cannot see any markings
on the jaws or the body of the chuck that advise which jaw goes where.
The problem is I chucked up a piece of round stock and it had over
..015 runout. I then got a piece of drill rod and it was the same. That
is of course unacceptable. So I checked the spindle run out and it is
in the area of .0005. I believe that is mainly due to the vibration of
the lathe. The thread on the spindle amd the backplate is a 2.25"x8.

So I took all of the allen head bolts out to seperate the backplate
from the chuck so I could check the runout of the backplate. There
were 6 bolts around the outside and 6 bolts around the inside where
the through hole is located in the chuck. The backplate will not come
off. I tried a deadblow hammer. I tried a cold chisel to try to
seperate the two and I tried WD40 to try to break it loose. It did not
budge. Any suggestions on how to get the back plate off? I kicked
around the idea of making a dummy spindle and threading it. Then screw
it into the backplate and give it a whack with the deadblow. Only
problem is I don't have any stock that big right now. Any other ideas
greatly appreciated. Thanks, Steve