"mac davis" wrote in message
...
My problem is that whether I use a tenon or a base, the bowl won't
true on the chuck.... a neighbor that works in a machine shop thinks
that the base or tenon might not be true with the face of the bowl and
that if it isn't, the bowl won't true out no matter how much you carve
away at it...

Logic tells me that if something is true when between centers, it
should be true when chucked, but I must be missing something here...

I had "assumed" that anything that could be chucked could be trued,
but maybe I'm putting way too much faith in the chuck?

BTW: I used the Talon on the Shopsmith for 2 weeks before I got the
Jet, and it seemed fine...

What jaws are you using? If you're using the serrated type
http://www.oneway.on.ca/chucks/talon.htm you're going to have to expend
extra effort in reverse chucking. These distort the wood as you tighten
them, especially if you _tighten_ them, like the "Key Features" section
implies with its "power clamping" bullet.

What keeps the thing true is the part you jam up against the flat you made
in the base, so you want to have that tight up against the chuck before you
begin to secure it. Make sure you've got a good center mark, snug the
tailstock up into the center, and then tighten the chuck. Still won't
always be perfect, because the design is such that it can't hold a wooden
circle without distortion, exacerbated by the symmetrical serrations, but it
will be as good as it gets.

Better is the dovetail hold, where smooth jaws can be secured outside or
inside a smooth circular section, then wedged against the flat section
outside the tenon or inside the recess as they are expanded/contracted. It
can hold a circle without distorting it. Just make sure that you cut a
slightly steeper angle than the steel so the wedging action engages before
the "grip."

So the critical factor in all is the flat surface formed by the nose of the
closed jaws, which should still be flat as the chuck opens. If not that,
never will run true save by accident when you reverse. If you've got the
jaws in the picture, I suggest you use them for single mount turnings, and
hope that you don't take so long that the piece begins to dry and contract,
because resecuring will always be a crapshoot.