Just following up on my thread... Well, here is what I did: I used 1 Circle Cutter, 3 1/4" plywood boards, 1 drill press, 1 jig, 1 dremel tool, 1 table sander and a partridge in a pear treeeeeee. Seriously, using all those things I am now the proud owner of 6 almost perfect plywood center rings and 2 deformed center rings. Thanks for everyones suggestions and help.
Here is what I did:
1) Make a jig (thanks Milo) with a right angle and clamp it to the drill press.
2) On the boards, mark the corner to go into the right angle.
3) Measure and circle cut (thanks Electrode) the center ring. By measure I mean stop frequently and put the motor tube in the hole to make sure everything is fine.
4) Once the first one is cut, cut as many as you have wood for. If you are like me, you will screw up a few so make more than you need.
5) After all the center cuts are done, measure and circle cut one of the outside cuts. This time use the body tube to measure.
6) Once you have cut all the rings, they will probably still have a lip on them, so you put all the rings on the motor tube. Pushing them all together you can then use a table sander to sand off the lip.
Voila. What you have left should be X number of equal center rings.