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Why Does a Timing Machine Sometimes Not Work on a Vintage Watch?

Q: Why Does a Timing Machine Sometimes Not Work on a Vintage Watch, even while the watch keeps good time?

A: The "tick" of a watch, of a lever escapement, is actually a repeating cycle of five separate impacts in the mechanism. The machine has to be able to pick up on this rhythm to tell anything at all. Sometimes there is too much other noise in there from something rubbing, the roller being too small and knocking, the pallet hitting the banking pins too hard, hairspring "singing", wheel missing a tooth, worn escape, excessive end-shake, whatever... and the machine can't lock on. In general extra noise, rubs, impacts, friction, etc, or all inefficiencies that extract a little power with each cycle. But a watch can run very inefficiently and still keep OK time, over the course of a day.

The machine also needs to detect the beat rate in order to get the timing. I have seen slow beat watches that have had a fast beat hairspring put in, then other parts changed to compensate (this is pretty common in older Elgins). The machine then reads wildly inaccurately, if it can work at all. Often it helps to turn the amplification down on the machine. Sometimes the machine can't detect the beat rate, and setting manually will help. But sometimes it just won't work.

When the rate is way off, the machine may not be able to detect anything, mostly because it can not get a handle on the beat rate. A watch that does not have a lever escapement, a cylinder or pin-lever escapement watch for example, is right out. The machine will not work because the sound of the watch is completely different.

I think timing machines are more limited in their use on the older movements. I use one as an initial reality check, but I test all the watches for several days in positions to do reasonable adjusting. The machine, even when it works fine, measures the rate moment to moment. But the rate actually varies a lot over the course of the day both because of positions, and because of the properties of the mainspring. Watchmakers of old did not much concern themselves with the rate at any given moment for this reason, but were more concerned with the drift over longer intervals of time.

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