Often those marginal things are hard to pin down since trying to get a look
at what is doing it often makes it work flawlessly!

I had a sideboard clock like you suggest, This always stopped at the same
time, but if you jacked it up one side to about the height of a cassette
tape it ran all day. I don't have it any more!

Brian

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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

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"NY" wrote in message
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We have a (clockwork) chiming clock. A few months ago it was cleaned and
re-fettled by a clock restorer (previously it didn't go at all). After
several months, it has begun stopping. Clearly it will need to go back to
the repairer.

But the exact symptoms are intriguing. I've noticed it always stops at
12.57. The hour-chiming mechanism kicks in at an indicated time of xx:00,
several minutes later. The clock only ever stops at night - ie 00:57
rather than 12:57. It also only does this every few days, not every night.
During the day it runs perfectly.

Is it plausible that a fault (eg a damaged/dirty tooth) on the hour-hand
gear which revolves once every 12 hours could cause the clock to stop,
given the very low gearing and hence torque-multiplication between the
pendulum/escapement gear and the hour-hand gear? Could such a fault
reproducibly stop the clock at 12:57 (with no latitude either side) And
could this only affect the clock at night (eg when the house has started
to cool down)?

Presumably the peg that initiates the chiming mechanism exerts a slight
back-pressure on the gear train. Is it likely that this back-pressure
would be greatest for one hour-chime than another - ie is it significant
that it's after the longest chime (12 bells for 00:00/12:00) and before
the shortest (1 bell for 01:00 or 13:00)? Or is that a red herring?

It doesn't seem to happen more often when the clock's mainspring is less
fully wound.

The clock repairer will sort it out, but I'm curious about the physics of
it?