Today I made the crutch assembly and ran the clock for the first time -- always a thrill!
The crutch is an example of the "one-legged" variety. That is, the usual fork is replaced with a small weight which rests against the pendulum rod. The at-rest position of the crutch is beyond the far side of the pendulum rod, which means that the weight is always in contact with the pendulum rod. The result is that there is no loss of motion in the crutch, nor does it generate any noise. This arrangement has proven itself well in past clocks.
The crutch is attached to the pallet arbor with a slitted collet. The collet is first drilled to a size a bit less than the pallet arbor. Then there is a blind 1/16" hole drilled in it, which will hold the 1/16" material which will be bent to form the crutch rod. This material is soldered into the hole in the collet with a bit of soft solder.
The collet is then slit in the lathe, using a small slitting saw, as shown in a previous installment. Then the hole in the collet is then broached with a clockmakers broach to make a snug fit on the pallet arbor. The grasp of the slitted collet on the pallet arbor must be tight enough to prevent slippage in use, yet loose enough to permit beat adjustment. Should the collet become too loose when fitting, the slit can be closed a bit with a pair of pliers or by squeezing in the vice. This arrangement has also proven itself well in past clocks.
The crutch rod is bent as shown in the picture with two pair of smooth-jawed pliers, to prevent plier tracks on the crutch rod. The weight is made of a piece of 3/8" brass rod, drilled with a 1/16" hole to fit over the crutch rod and held in place with Loctite 290. In the picture, the excess rod has not yet been trimmed off.
The worries I had about the working escapement have turned out to be unsound. I worried that there would be too much overswing, which would bump the end of the pallet into the escape wheel. Such has not proven to be the case. I had also worried that the mainspring would proved to be too weak -- not enough overswing, or a clock that wouldn't run. There is the proper amount of overswing for a deadbeat escapement.
I had also thought that I might have to thin the pallets -- the escapement was designed with very little drop. But the drop clearance seems to be enough to prevent the pallets from catching on the backs of teeth. As a result, the movement is very quiet, like a French clock. It always feels like a real accomplishment to get a homemade clock to run!
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