Something was off. I did manage to get the ring sections joined with the help of a strap clam and a big rubber mallet. But they didn’t want to close up, so I left everything clamped to the table and called it a day. It was New Year’s Eve so to time to go “celebrate”. I opened what I believe to be a 20 year old bottle of Mumm’s Champagne. It wasn’t very good and the remaining half will be dumped.
Today I looked carefully at the parts and the jig. Some sections had broken off the parts. As far as I can tell, the X axis of the fixture was slightly off parallel to that of the machine. It’s also likely that my XY0 was a millimetre or so to the right of where it should have been for a symmetrical cut. I added a reference board to the fixture which I will machine to a height to use for alignment in all 3 dimensions.
The other issue was that since I hadn’t allowed for the joint length, the wall sections are shorter than I had planned. So I cleaned up the widest 8/4 board I have and cut 11 new sections. This board is about 190 mm wide, so by the time the sections are cut they should be near the 170 mm that I want. That will get me back to the 550 mm or so finished diameter. I also added a bit more relief to the mortise pattern to make joining the pieces easier.
While I was doing the last few cuts I thought the bit was sounding slightly strained. It’s at least 10 years old and has seen quite a bit of use. So I ordered 2 new ones at Amazon. One’s an Amana 2″ and the other a Freud 2.5″. They won’t be here for at least a week, making this an even more long-term project.