Making Metal Clockworks for Home Machinists. Stan Bray
are made. The spindles act as punches to locate the hole positions in the plates.
The tool is now used to set the distance of the third wheel, which cannot be sited on the line because it would then be impossible to mesh all the wheels properly. There is no specific angle at which to set the third wheel and this, plus whether it should be set to the right or left of the line, is a matter of individual taste. Generally speaking, an angle of about forty-five degrees is used; whatever happens, make a note of the angle just in case it needs to be referred to later. Having decided where the wheel will be going, repeat the operation with the depthing tool so that a mark is made for the third wheel pivot hole. From there the tool is used to lay out the distance from the third wheel to the escape wheel, and exactly the same procedure is used. The mark should be made on the line used by the great wheel and minute wheel, and that is the clock train marked out. Holes for the pivots can be drilled, but don’t forget they should be drilled undersize. When the plates are separated, they can be opened out with a taper reamer so they are a nice running fit with the pivots.
There is still one more operation required in order to make all the pivot holes, because the pallets of the escapement also need to be set. The pallets and the escape wheel are mounted in the depthing tool and adjusted until they work smoothly in the same way as before.
Makeup of the plates, showing typical position of pillars and back cock.
The plates are now complete, except that if the clock is to use a pendulum, a back cock must be fitted. This is a bracket that supports the suspension for the pendulum, which can be fabricated or milled from a solid block of brass. It takes the form of a bridge to clear the pallet arbor, the pivot of which locates in a hole in the cock, the suspension being fitted on the arbor between the plate and the bearing. It is essential for the good running of the clock that the cock is secured firmly to the plate and will not work loose. It is also essential that the escape wheel arbor when fitted to the cock is at ninety degrees to the plates.
Some people like to fret out the plates to make an attractive pattern, and this is a matter of individual taste. The fretting will obviously need to be done with the plates secured together. One way of doing this is to draw a suitable pattern on paper, taking care to avoid all pivot holes, cut out the pattern, stick it on the plates, and cut around it. Do not try and chain drill, but drill a couple of holes in strategic places, and use a piercing saw or a power-operated scroll saw, if one is available, to complete the job. Finally, clean the edges of the cuts using small files.
The back cock in position and the crutch temporarily in place.
Something rather unusual in back cock construction, consisting of four spacers and a plate, which is bushed to accept the escape wheel arbor as the plates, in this instance, are made of steel.
The plates in position and the movement assembled.
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