On Thu, 8 Apr 2021 13:59:02 +0100, "NY" wrote:


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?


The greatest resistance is not necessarily allied to the most bongs.
There could be a snail-shaped cam in there which has its greatest
distance from the pivot at midnight. This would imply that the clock
knows the difference between night and day in order for the user to be
able to silence the chimes at night.
--
Dave W