I was making these for a friend who decided to just sell her 13.1 Odyssey - perhaps an ATM here can use them. 5/8" Appleply, 16 5/8" O.D., layout lines marked at 45 degree intervals for location of compression tubes/truss attach points, and focuser. OD edges finshed with 3/32" roundover. I.D. is uncut, laid out at 13 9/16", but can reduce this dimension to as little as 12 1/8" and recut O.D. as needed, but would charge a bit more for the redimensioning.
I use a Micro Fence circle cutting jig coupled with a Dewalt DW621 plunge router, a combination which allows me to hit precise, repeatable dimensions. If desired, I can also cut pockets for 1.25 aluminum compression tubes, so you're pretty much ready to assemble the rings after finishing. I'm working on my new 18" in the garage and it's convenient for me do work on these in the near future. No real idea what to charge, so let's say best offer over $30 for the pair, shipped. - more if we recut everything.