Ok, let's not call what I described a jam chuck -- let's call it
something which works well for me and for everybody who has copied this
design (such as it is) and is CHEAP.

My feeling is that the system I use works in all cases where cole jaws
will work also. But, cole jaws will not work in all cases where my
system works -- natural edge bowls, for instance. So, storage space and
money being limited quantities, why should I have both?

Bill

Derek Andrews wrote:
Bill Rubenstein wrote:

I don't like cole jaws and such because... Even when the blank is
dry, the rim is never going to be 100% because of the release of
tension in the blank as wood is removed.


Unless you are looking for an absolutely concentric fixing, which
generally isn't necessary, I can't say I have ever found rim distortion
to be a real problem when using cole jaws.


That said, the best way of driving a reversed blank (IMHO) is jam
chuck it with a chuck made so that the driving force is applied pretty
close to the bottom of the bowl.


I'm gonna be pedantic about semantics here, and say that what you
describe is not a jam chuck, or at least it is contrary to my
understanding of the term.

I have always considered a jam chuck to be a piece of scrap wood turned
to exactly the right size such that a small bowl (or box etc) can be
jammed onto it and held securely in place without tailstock support. The
jam chuck may grip either inside or outside the turning. If the fit is a
little sloppy, a paper towel may be used between the jam chuck and the
turning.