Ok, the deed is done - so I'm really asking this after the fact. I cut the parts for a plywood coaming yesterday (generally using Tom's instructions). It's 3 1/2" rings with a 1/4" coaming lip on top.

The way that I did it was - I cut the coaming lip first. I then used that as the template for the inner-cutout area for the 3 riser rings. I drew the 3 all at the same time. I cut out the 1st of the 3 rings and used that for the outer-cutout area for the remaining 2.

(Whew, that was a lot to say - I used what I had already cut as templates for the others.)

Anyway, to say that they're not identical is an understatement. They're mostly-close, but I really had to take time to figure out what the baloney happened for most of them. They are, however, close enough for me - I've started epoxying them together and the basering to the boat frame. You can see the outer edge in the picture below - I don't have any real good pictures of the inside edge.

My question is - do you have any tips for the next time I go to cut 3 1/2 identical rings?