"Ned Simmons" wrote in message
...
In article M8qNf.53363$3W5.39831@trnddc02,
says...

"Dave Hinz" wrote in message
...
On Wed, 01 Mar 2006 22:30:51 GMT, RoyJ wrote:


I think it has to do with the fact that the ring with the teeth is not a
perfect fit on the chuck body. Tightening the chuck tends to cock the
ring a bit so it doesn't turn as freely. Moving the key to a different
hole pushes on a different point on the ring and frees it up.

Ned Simmons


You are on the right track. The fit between the chuck and scroll can wear
with use. When you tighten one hole it forces the scroll off center, so by
tightening all three you have equalized the forces on the 3 holes. Bringing
it back to center. Mostly noticeable on older worn chucks. I have seen one
chuck so bad the only way it would center up right was to use a torque
wrench on each hole.
Those who have older worn chucks know that the fit between the scroll and
chuck body is bad, and can lightly tap on the chuck jaw and dial in a part
in a 3 jaw with an indicator. Then start cutting. As long as you don't do
any heavy roughing it will continue to run true. This is a way to get a 3
jaw chuck with only 1 tightening hole in it to run true.
This is a different problem from having worn the jaws bell mouth. Which
is corrected by grinding the chuck jaws true.