Today I did some remedial work on the clock pallets. I felt there should be more lock, which is the amount of the pallet the escape wheel tooth covers when it falls on the pallet. If there isn't enough lock, the tooth might fall onto the lifting surface of the pallet. If there's too much, the opposite pallet will scratch the back of the tooth behind, which stops the clock. When I increased the amount of lock by raising the escape wheel a few thousandths, there was insufficient clearance and the tips of the pallets scraped the backs of escape wheel teeth.
There are three things you can do in such circumstances. One is to make the backs of the escape wheel teeth to have a steeper slant -- pretty difficult, after the wheel is already made. Another is to decrease lock, which I didn't want to do. The third thing is to thin the pallets, which is the option I chose.
Normally, I consider that the thickness of the pallets will be 1/2 of the tooth pitch (the distance from one tooth tip to the next tooth tip) minus about 0.020", for the clearance. These pallets were somewhat thicker than that, so it was quite safe to thin them. The final measurement was about 1/2 tooth pitch minus 0.015", which still left a tight escapement, but enough clearance. It's better to have too much than too little clearance here.
The pallets were thinned by laying them on a piece of wood, then using a rather heavy and somewhat coarse India stone to thin them. The stone is supported on one end by a piece of round material about the same thickness as the pallets themselves. This piece of material forms a roller, which makes it possible to roll the India stone quickly back and forth over the pallets. The cutting process is rapid, but not so rapid as to be dangerous, as it would be if power equipment were used.
The only way to do this job is to thin, measure, and then try out in the clock itself -- until the proper thickness is achieved. Rather laborious, but successful. The finish on the pallets is not too smooth at this point, and when I'm convinced the clock is operating properly, they will be repolished.
I also inserted longer 2-56 setscrews in the pallet arbor end-stones, which made it possible to use tiny locknuts. This makes it possible to more closely adjust the escapement.
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