When I rough turn I make a tenon at the base of the green wood blanks
The problem is once the blanks is dry the tenon becomes oval. I have not
yet found an ideal way to true the tenon before placing it in the chuck
for
finishing.

Dennis,

Get a copy of Bill Grumbine's video on turning bowls. He addresses and
demonstrates a very simple solution to that problem. Bill's address is:
http://www.enter.net/~ultradad/ The disk or tape is well worth the cost.