Chiming clock always stops at the same time - but only at night

[NY]

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?

[gareth evans]

Firstly, do you mean the strike (counting out the hours) rather than the chime (The quarter hour bongs)?

I suspect that the problem will lie with the date advance at midnight; the hour hand rotates twice in 24 hours, but there is another wheel geared down at 2:1 to advance the date. I suspect that the spigot that advances the date wheel is riding onto the surface of the date wheel instead of pushing it along.

May I suggest that you join the clocksgroup in groups.io?

[Brian Gaff (Sofa]

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

[Andy Burns]

Do we even know whether this clock tells the date?

[Adrian Caspersz]

Do you recall Shell Beach as well? :-)

[NY]

The clock does not have a date display.

It has two chiming mechanisms: the Westminster chimes every quarter hour and the striking on the hour. When I said "the hour-chiming mechanism kicks in at an indicated time of xx:00", I meant that start of the chiming sequence. The bongs follow a few seconds later after the chimes have finished. Without a seconds hand I can't say how accurately the start of the chiming sequence or the start of the striking correlates to the xx:00:00, but I think the minute hand is pretty close to the 12 position. I imagine that's one of those things which a clock repairer adjusts. He'd probably need to remove the hands to remove the face so he could get access to the front face of the mechanism. Given the cost of the repair, it may have been a complete dismantle, clean and reassemble, maybe even with re-turning some of the shafts and fitting correspondingly smaller bearings - but that's all supposition.

Anyway, it's not date advance because there is no date dial. Do date advance dials move continuously as the day progresses, or do they move suddenly from

20 to 21 etc at midnight? From your description of "geared down by 2:1" I presume it's the former.

At least the clock hasn't started chiming 13 so I won't be finding a Midnight Garden anywhere - and anyway, my name's not Tom ;-)

[Max Demian]

To determine the number of strikes there is usually a "snail cam" (stepped), and there is a lever which drops onto it just before the hour

- you may be able to hear it. (The sound is known in horological circles as the "warning".) Perhaps the lever that drops is incorrectly adjusted so it fouls on the cam - it will be at its highest for 12 strikes. I suggest you watch the mechanism carefully. There's no reason why there should be any difference between 12 noon and midnight.

[Martin Brown]

Or Earl of Bridgewater but his did it at 1pm for end of lunch break.

The canal in Worsley itself is an interesting orange rust colour from the mine drainage even today or at least it was last time I looked.

[Dave W]

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.

[Steve Walker]

It definitely still is.

[Brian Gaff (Sofa]

I was very surprised when I looked into the back of the clock I no longer have to see that there were in fact no bells at all, just some loosely coiled springs that rang at different notes, however it is indeed the case that the device that cocked the chiming mechanism, operated by another clockwork motor did in fact prepare itself very slowly by raising the various hammer things a couple of minutes out, but that this raising and lowering during the strikes was obviously faster, as it was, presumably driven by the other clockwork mechanism. It all seemed very complicated to me, but I suppose there are a lot of different designs due to history. Brian

[The Natural Philosopher]

Its colder at night typically