xray wrote:
I have a lathe with a 2 1/4" threaded spindle with 6 tpi. It came with a
3-jaw but no 4-jaw chuck. I got an 8-inch 4-jaw off ebay that didn't fit
and then a cast iron backplate which had the proper thread. Saturday, I
cut down the backplate to fit the chuck and drilled and tapped it to
attach.

First time I used it, it got no heavy loading, but I though I was never
going to get the chuck back off. Eventually a bunch of hammering on a
lever bar broke it free. The 3-jaw has never needed more than a couple
hits with a dead-blow hammer, even after I jammed a tool into the work.

Is there anything obvious I should think about to keep it easier to
remove? The main interface between the backplate and the spindle seems
to be the flat surface on the backplate that is about 3 3/8" in
diameter. I never turned that part of the backplate, but I have since
polished it with some fine emory and greased it.

Anything obvious I should do beyond what I have already done?

Clean the inside of the backing plate with solvent, and then mark
it with dy-kem, Hi-Spot blue, or even magic marker. Screw the chuck
on and back off, and the place where the dye is removed will show
where it is binding.

Jon