wrote in message
...
On Feb 9, 8:29 pm, mac davis wrote:
On Sat, 09 Feb 2008 16:32:06 GMT, Owen Lowe wrote:
Having a form cover the chuck key area is a real pain when it happens.


If you have a hollow form like a bowl that you want to hold with the
jaws from the inside, for whatever reason, it could cover your chuck,
however, if there's only a inch or two between the chuck and wood, you
couldn't get you ball-end hex-key in there either, so there's and
advantage only in limited cases.

You could also use a pin chuck to handle such cases. Once again, rare to
change based on inside with no sign outside, but a new hole equals a new
hold.


To come back to the jaws and chucks, where numbers of jaws available
to cover the gripping size from small to large, is seen as an
advantage,
I see them as a limitation, or the result of a limitation, as it is a
result of limited jaw travel being available on a chuck, and they are
always there, or else you would need only one set of jaws, .....but
having a chuck that has a longer travel, is a distinct advantage, as
one set of jaws is able to do more.
This also means less often changing jaws and less money invested in
more different size jaws and/or extra chucks.


Of course there is an advantage in jaw choice over jaw travel. Circularity
is achieved at only one point, and that is the key to holding the piece well
and undamaged. Long travel means less-than-optimum holds must now rely on
less force per unit of contact area, often crushing that which they hold.
If you like, you can avoid a step or two and finish up the bottom of a piece
before you hollow it, leaving no need for vacuum chucks or jam chucks.

Jaws with wider faces are especially well-suited for tenons because they
don't take much wood to fill a circular center, and provide a large bearing
surface to stabilize against the shoulder.