Striking a balance
Striking clocks have an endless variety of mechanisms to achieve the desired striking effect but the vast majority of those that do not have a countwheel system have a toothed quadrant, a gathering pawl, a pin wheel to trip the hammer arbor, and a guard wheel with a warning/let-off pin. The pinion of the guard wheel arbor is often driven from the pin wheel.
After a movement has been stripped to service it, it is necessary to assemble these components in the right relationship to each other, particularly the hammer trip and the pin wheel. There are endless relationships that are incorrect and only one that is correct. This is when the hammer trip just clears the last pin before the mechanism locks on the last strike, when it then is clear of the next pin both at rest and, more importantly, after the warning has run. Very rarely do the original makers mount the bearing of the guard wheel arbor on a separate cock so that this relationship can be easily adjusted. Normally one is committed to separating the plates and moving the engagement of one of these two wheels/pinions a tooth or more. This can be frustratingly awkward as everything moves and the end result can often be another incorrect relationship. Variously marking the teeth and tying up the pieces helps a lot but it is still a pain.
Yesterday, while faced with this so-familiar problem (the hammer was just on the rise at warning), I was returning from the grocery store and had an idea. The gathering pawl is fitted to a squared extension of the pin wheel and more importantly it is easily available without any disassembly: suppose I moved it 90o on its squared shaft? Would it change the relationship or was this constant irrespective of the phase of the pawl? I moved it one square and that made it worse. (Hurray, the phase does change!). Another 90o move and the relationship was perfect. Problem solved without any disassembly!
Now I am not saying that this will always work. It obviously depends on the original incorrect set-up and on the basic parameters of the design but it is, equally obviously, worth a try. There are only three other positions for the pawl on its arbor and they can all be run through in under three minutes. If it works you have saved probably an hour and much muttering; if it doesn’t work you have wasted three minutes. Maybe next time!
Ted Wale, Canada
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