Yesterday morning, with only about 200 picks to go to finish Piece 3, I unpicked 400 picks trying to figure out what was going on as regards sporadic lifting of Shaft 12. Plain weave and individual shaft lifting worked fine, but not my design draft. I wove and finished Piece 3, but I had to give up on the faulty shaft for the last 2 or so inches of weaving; I'll have to sew it in. I took off Piece 3, and went hunting for the problem/solution. I discovered a) it wasn't Shaft 12 but 11 that's been naughty, and b) it was caused by a part wearing down and not catching when it's supposed to.
On my retrofit computer-controlled loom, information on the draft gets translated into movements of these tiny sticks (below, yellow) seen here about the size of an eraser at the back of a pencil. For shafts which are supposed to lift, the "eraser" is raised, pushing up the "wedge" in the top picture, so the wedge is caught by the metal piece and pushed to the right, thus lifting the shaft. I don't know if a piece broke off or it gradually wore down, but now the wedge catches only sporadically.
A wee while ago I noticed that a screw had come off while weaving; I could have sworn it was one of the top ones, but Ben thinks it was the green one, which is connected to Shaft 11. I also noticed the bottom of the Shaft 11 wedge (pink) was dirtier and a bit more damaged than others.
At any rate, I'm gritting my teeth and hoping I can get at least one more piece woven before Friday because I need more than three. If Shaft 11 fails me this morning, I'll make a 15-shaft draft and not use 11 altogether.
I'm not enjoying this at all. Ben says replacement of the wedge pieces is going to be expensive. Just what I needed.