The CRW tool crib has a small shop made Longworth chuck (12")? that members can check out for 1 month at a time. If interested, check out with the tool czar at a club meeting.
To view this YouTube video, click on top chuck image, which demonstrates how to make a similar one and use by Brian Proctor.
The Longworth type chuck is used to hold a bowl, so the bottom may easily be turned to finish and embellish as desired.
Bob Raasch