wrote in message
oups.com...
The adjustable 3-jaw like Grant has can be more accurate than collets,
especially cheap collets, and holds the piece more solidly so it
doesn't slip while you are threading and mess you up. I like 5C collets
a lot but there are only a few things they can do that a good 4 and
set-tru 3 jaw chuck can't match.

If your stock is slipping in your 5C collets, then I suspect the following
problems:

1. Not enough clamping pressure applied to the collet.
2. Collet bore dirty or oily, or chips stuck in the grooves between the
collet "fingers".
3. Stock size not correctly matched to the collet bore.
4. Cheap, out-of-round collets.
5. Taking WAY TOO BIG a cut.

Otherwise, they should hold your stock more securely than a jawed chuck
(it's all about friction and surface area). Unless of course you are
tightening your jawed chucks to the point where they are digging into the
stock; then you're changing the rules of the game.

Btw, the same list of problems go for tool slippage in R8 collets.

- Michael