No updates in a while... but it's not out of my mind.
This is a mockup of a fixture for the bottom bracket and dropouts. I want to start from here because I'm so worried about tire clearance. It's much different from Calfee's. I think I'm going to build it like this, cut it to 8" wide, and then put shelf brackets on it to put it 90deg and 4" centerline from the plan. This specific version didn't quite work for a couple of reasons. First because the 1-1/2" angle iron has holes that are at 1", not 3/4" from the angle, and so I can't get the 5-1/2" spacing I need (the difference between 5-1/2" and 135mm can be cheated with the hole clearances). I could get the right spacing with the angles set outside the dropouts, but then the whole stackup is too wide. The other reason is that the fold in the angle iron is not square. I think I saw some 1.5" box section that should fix both problems. That mounted on 4" centers should do it.
The fitting shown is for 2" pipe. 2" pipe is actually 2.375" and that's just over the size of a regular MTB tire, so a fitting that goes around that should be 2-3/4", perfect to set the clearance. I wanted to use a piece of 2-1/2" pipe which is really 2.875", but I couldn't find any. It's an oddball size.
I'm back to debating whether to use 29er or 27.5 wheels. The latter are becoming more prevalent and easier to find cheap tubeless versions; it also makes the tire clearance easier, both in the angle of the chain stays, and behind the seat tube. When I look at the
Marin Bobcat Trail geometry, the 27.5" version spends the reduced stack to add some reach.
Untitled by
Darth Lefty, on Flickr