I use a method that I've used for years which probably came from Malcolm Tibbetts. I have a 12" x 12" x 3/4" MDF board with concentric circles labeled with their dimension. There are 8 - 16 small holes drilled equadistant around each circle. I buy waxed paper from the dollar store and for each ring, I tear off a piece to fit, place it on the board and insert nails in the ring just bigger than the target ring and put a couple rubber bands around them. I then squeeze glue into the center of the ring and then dab a segment in the glue and use it to spread glue to the next segment and then loosely join the segments. I then pull two opposing nails and then two more opposed to them and repeat until all nails are removed. I'll add more rubber bands after that if necessary.
I've tried all sorts of methods, but seem to keep coming back to this one as it seems to give a good amount of clamping pressure.