Friday, December 21, 2018

Clock 4 pin escape wheel

One of the defining features of Woodward's intermittent grasshopper escapement is the large pin escape wheel.  It is intended to be let off once every minute, so there are sixty pins.  After considering the possibilities for how to index, drill, and make the pins... here is how I proceeded.

Since I print the pattern and glue it to the wood, indexing is "sort of" not a problem.  I started by center punching each pin location.


Since I don't have a drill press, I set up the lathe to index each of the punch locations and drill as well.  The spacing between pins may be accurate enough, because when the drilled holes make their way around to the indexing pin, they're slightly off from the center punch dents.  But it at least this setup ensures that the pins are all the same distance from the center of the wheel.


After initially thinking of steel, then brass pins, I decided that metal pins might be rather loud.  So instead, the pins are made from toothpicks.  They are roughly cut to the right size.


Then they're staked into position...


... the end sticking out the bottom clipped off ...


... and then carefully planed flush with a chisel. 


After all this, I went through and cut off any pins that were longer than the rest, probably to within a 0.5 millimeter or so. 


Here is the escape wheel trial fit in the frame.


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