Quote Originally Posted by mklotz View Post
Believe me, you don't want a self-centering 4jaw. The independent 4jaw is both more flexible and more accurate.

Centering work in the 4jaw can be made much less tedious with a few homemade tools and a straightforward procedure. You may want to read my procedure here...

Centering work in the four jaw chuck

With this procedure, another dead simple addition can make centering polygonal stock much easier...

Centering aid for polygonal stock
I think a self-centering 4 jaw would be good for production in a shop that does a lot of turning of square stock. As long as you can tolerate the several thousandths of runout, just like with a 3 jaw chuck and round stock. Depends on how critical low runout is to your part, and how many of those parts you need to make. If you're making rocket parts, it's probably not going to be what you need. I'm probably never going to buy one. But I'm not doing production work, and I can take all the time I want to take to dial stuff in to ridiculously tight tolerances if I want to do it that way. YMMV! It almost has to.

Bill