Calculating pendulum length

[Bodger BrianParticipant @bodgerbrian]

In a very rash moment, I’ve purchased a cheap second-hand weight driven clock movement, as I wanted to have something to strip down & re-condition without worrying about wrecking a family heirloom or my bank balance if it all goes horribly wrong.

There was no pendulum with the movement and as I have absolutely no idea what type of clock the movement came from (I can’t find any maker’s mark or name anywhere), I thought as my first exercise, I should work out the theoretical length of the pendulum I would need, if only to give me some idea of what case I could put it in when finished.

The train is as follows :-

Escape wheel 40 teeth/8 pinion -> 72 teeth/8 pinion -> 80 teeth/60 pinion -> centre wheel 30 teeth.

After a lot of internet searching, I THINK that gives 60 BPM and a pendulum length of 39.2 inches.

Can some kind soul either confirm my calculations or put me right if i’m wrong?

Thanks

Brian

[Bodger BrianParticipant @bodgerbrian]

Can someone confirm my workings?

[Neil WyattModerator @neilwyatt]

I make that 1,800 steps*, so the period of the pendulum needs to be 2 seconds, so I think you are right.

Presumably it's from a long case (= 'grandfather' clock.

Neil

*just to be clear the escape wheel moves 1/2 a tooth as the pendulum swings each way so a 2-second period=1 second between 'beats'.

 

 

 

Edited By Neil Wyatt on 17/02/2019 20:23:28

[Bodger BrianParticipant @bodgerbrian]

Neil – thanks for the confirmation. I was pretty sure I had it right, as every other way of calculating it I tried gave nonsense figures.

I'm glad the pendulum length confirms it as a long case clock, as I quite like the idea of having one. As it's only the movement I have, I don't feel too constrained to match movement, dial, and case etc so it'll probably end up as a bitsa-clock.

I think my next step is to figure out how the striking mechanism works before I dismantle it. I have a book by Donald de Carle that was recommended to me a while ago but I don't find his descriptions particularly easy to follow or match to the accompanying diagrams.

Brian

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