Ignoramus30636 fired this volley in
:

This would seem to be quite acceptable for things such as making
gears, and whatnot?



In addition to what Pete said, it also depends upon whether or not you'll
machine all surfaces. If you start with slightly oversized stock, a 3-
jaw will be more convenient; so long as it's tight, the work will
ultimately be centered as well as the run-out of your table, not the
chuck -- because you'll be machining off any "out of roundness" to the
piece.

If I'm machining (say) a hex profile from round stock, I start out with
stock only a few thousanths greater in diameter than finished piece. I
know my 3-jaw will center within a couple of thousanths, and the milling
takes up the "slack" in the precision of the chuck.

If you're doing spot-work on an already-machined piece, you'll need more
precision, which you can get with a 4-jaw and some indicator work.

LLoyd