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. All of the bowl is going to move but the
rim will move the most -- I suspect that one cannot find any bowl which
would stand up to flat and completely round rim as measured by a good
method.

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.

Assuming that you have a 4 jaw chuck... To make a cheap jam chuck, get a
piece of schedule 40 pvc joint (the thing you use to glue two pieces of
pipe together) which will cost you well under a dollar I think.

Expand into one end of it to hold it and true up the free end. Scrape
unless you want some nasty catches.

Now reverse it and true up the other end.

Here I make a half round indentation into the end and glue in a piece of
1/4" diameter buna cord -- Packard sells it for about $10.00/5'.

Another approach which I have not tried but I bet will work is to round
over the free end and coat it with a silicone material -- some of the
gasket-making stuff you can get in a small tube at the auto parts store.

Another, even less costly approach, is to cover the end with several
layers of duct tape.

Then, you are done.

To use it, jam the reversed bowl between the chuck and the tailstock.
You can add a piece of paper towel to keep the gasket material from
marking your bowl. You can take the center pin out of the live center
so as not to mark the bottom too deeply or you can use a home-made
something which covers the tailstock pins.

Now you can detail the bottom except for a small section which you can't
get to right in the middle. You do that by hand.

Now, I usually use vacuum chucking and I have just described to you how
my vacuum chuck was made, almost. The only change to the above was a
method for keeping the vacuum in spite of a 4 jaw chuck being pretty
leaky! That is for another day.

Bill

Derek Andrews wrote:
Kevin Cleary wrote:

Does anybody have a good method for finishing off the bottoms of bowls.


No one so far has mentioned vacuum chucking which is another option to
consider, though it is expensive and I have yet to bite the bullet

If you want to reverse turn, the technique you use depends on the rim
design. For example, a bowl with a natural edge cannot be held with
anything that grips around the rim. A bowl with an in-turning rim
generally cannot be held in a standard cole jaw. I have made special
grippers for one of my popular bowl designs, but it's a lot of work for
a one-off.

try some of these google searches:

doughnut chuck

longworth chuck

vacuum chuck

cole jaws