Actually, if you use a good dial indicator with a four jaw chuck, you can
turn perfectly round stock. (zero runout)
If you do the same thing, you can turn a round post on square stock(good for
cam lobes), or elliptical lobes for whatever....
nice thing to have for extra precison... good luck.

"Waynemak" wrote in message
...
My dad is getting up in the years and is cleaning out some of his
unused/nolonger used tools. He gave me a 8" 4 jaw chuck that was made in
Germany. It has never been used and will need a backing plate. It is a 4
jaw with self centering jaws, I have not come across any of these in my
travels. It must work well with square stock and would work just as good
as a 3 jaw on round stock, any other things I am mising?