George has already given a link to the Longworth Chuck on my website.
I just put up a new review on the Rim Chuck being produced by Richard
Benham in Oregon. The link to this review is:

http://www.fholder.com/Woodturning/Rimchuck.pdf

I've just tried this chuck and find it better than Cole Jaws or the
Longworth Chuck. It may be a bit pricey for many of you, but it is a
good solid chuck that is easy to use to turn the foot of a bowl.

Fred Holder
http://www.fholder.com

Here is a homemade version of what Fred has described. I haven't made
this one yet because i can't for the life of me figure out how you
center the bowl into the clamps before turning the dang thing on (I
prefer to understand how something works prior to spending time
building it). Good luck.
http://www.crwoodturner.com/longworth/
JD