I would never mount a 4 jaw in a 3 jaw chuck, however I mount a 3 jaw in a 4 jaw all the time...Phil
How about a 3jaw in a 4 jaw bolted to a 3 jaw?
Yes, I really did this. I have a 6" 4 jaw that I bolt to the front of my 3 jaw
for when I need it, and I was using it, and a "SUPER HOT" job came up, it was a
Saturday night into a Sunday morning thing, hundred parts or so, nothing critical,
if there was actually a print on it, there would have been a napkin, a sketch, and
the tolerance block would have said "Has to WORK".
So I just grabbed a POS 3 jaw I had sitting around and tossed it in the 4 jaw.
Not the best thing to do.
I see nothing wrong with grabbing a smaller 4 jaw in a 3 jaw for a quicky. I've done
it many many times until I made a plate that could bolt to my 3 jaw.
I've also chucked up a straight shank ER holder in a 4 jaw bolted to a 3 jaw.
Sometimes you just gotta do whacha gotta do.