Both the Bison backplates that I have bought, a L00 and D1-4, have
counterbores so the cap head screws are fully recessed.

Terry wrote:

Yes, I did undercut the shoulder. I do have an 8" 4 jaw chuck that I
use ocassionally on irregular shapes. This Bison chuck is replacing my
old 4" crafstman 3 jaw threaded chuck which was still very accurate and
with some tweaking of my work piece, I could get it down to less than
.001" runout. I tend to spend quite a bit of time with a dial
indicator making sure whatever I put into my chuck runs true. I was
hoping this new Bison with a properly machined backing plate would give
me some better results with less tweaking of the work piece.

I may pull it apart from the backing plate one more time and re-seat
it. If I can not get it any better than it is, I will just use it and
it will most likely be perfect for everything I do.

No one has mentioned if I should counterbore for the bolt heads on the
back of the backing plate. Is this typically done so the heads of the
bolts don't stick out? This would also give me more threads into the
chuck.

Thanks.