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I got everything working yesterday and it's now running smoothly - and for a surprisingly long time!

A couple of observations:

  • I really don't understand the purpose of the Pallet Fork Limit Screws. As long as the Impact Pin is within the fork the pallet fork is retained. If the pin were to come out of the fork, the limit screws don't adjust tight enough to constrain the fork, and the escapement teeth prevent any motion outside the normal working bounds. Scratching my head on this since someone else wrote they had to adjust them to get it to work properly.
  • The motion was very inconsistent at first. I'd get a few ticks then it would stop, or it would refuse to start altogether. I seemed to have solved this by filing the contact points of the Pallet Fork and Escape Wheel smooth. I also made sure the corners were very sharp. Initially my printer (Prusa i3 Mk3) printed slightly bulged corners and after watching the motion it was clear that this was part of the problem.
  • The adjustment of the Impact Pin definitely made a difference, but the mechanism is quite sensitive to its radial location, so expect to fiddle with it until the motion becomes smooth
  • I managed to "strip" several of the M3 nut pockets - in particular on the Impact Pin Housing. Not a big deal, but maybe a tighter fit or use of a square nut would be better here
  • I get quite a long run time with only a small (90-120 degree) wind of the spring. Anything more and the friction between the pallet fork and escape wheel (and I'm sure in multiple other areas) rises and diminishes run time. I think that if the Mainspring Assembly was stiffened up a bit (perhaps with a bridge between the two frame pieces) and some finely-sanded escapement surfaces it would run for a lot longer. I think I will try brushing some CA onto the contact surfaces and then sanding/polishing it smooth. That should create a lower friction coefficient, but we will see :-)