Nice 12 segment ring. Did you use the segeasy sled method?
I have good luck with a segeasy sled method for 12 segment rings. I have been doing 36 segments per ring for the last couple of projects. About 60% of my rings come out great and I can glue up the ring at one time. The others have enough gap that I have to build half rings. The errors I think is from my stock not being 100% perfect parallel and the wedge fences being off just a bit.