08/18/00
Today I began to make the arbors, beginning with the pallet arbor at the top of the clock. The escapement on this clock is rather peculiar. For one thing, the endshake of the pallet arbor must be limited because of endwise forces delivered by the escape wheel -- when the escape wheel tooth strikes the pallet face, it will push the arbor sideways -- to repeat in the opposite direction with the next tick.
So I will build a pair of adjustable "end stones" (acting like the end stones in a watch balance) which can be adjusted with a couple of screws to eliminate almost all of the sideways motion. The screws should also be able to function to equalize the drops, much as moving the pallets up and down do in a normal dead-beat escapement. (With this escapement, raising or lowering the pallets will change the lock.)
The end pieces were made from 1/2" brass rod, the same width as the plates (frames). A small hole, the proposed size of the pallet arbor pivots, was drilled into the end of the 1/2" rod in the Unimat lathe. Then, the brass was transferred to the Sheline mill, where it was clamped in the chuck atop the rotary table. The two mounting holes were drilled, rotating the rotary table 180 degrees. This makes the holes accuate.
The holes are drilled fairly deep, since both of the end pieces will be sliced from the same piece of 1/2" rod, using the cut-off tool in the Unimat lathe to make the cuts.
Next, the pivot holes were drilled through the brass plates (frames) in the proper place. This same small drill (which drilled the pivot hole in the plates and the small hole in the center of the end pieces) is used as an alignment pin to align the end pieces on the plates. That way the end pieces and the pivot hole are exactly aligned.
The end pieces are held in this place by a drop of Super Glue, which acts as an instant clamp. The screw holes (size 2-56) are drilled in the plates, and the Super Glue clamp is "released" with a small sideways force. (Use heat if stubborn).
Next, the center hole in the end pieces is also drilled to accept a 2-56 thread. The screw which fits in this hole is a 2-56 stainless steel Allen screw, which should be a good "end stone". The ones shown are 1/8" long. Perhaps some longer ones would accept a 2-56 lock nut to secure the operation. Or use Loctite 290.
After construction of the endpieces, the oilsinks were cut into the frames, using a homemade piloted end cutter (I'm going to do an article on how to make these -- very useful items.) The Allen screw will be down in this oilsink up against the end of the pallet arbor when the clock is going.
Today's links:
Drilling endpieces in mill.
Finished end pieces.
End pieces aligned on frame using drill.
Finished end piece with tiny Allen.
Pilot cutter makes oilsink.
Oilsink in frame.