General clock question about pendulums

[c.kelly]

Hi,
I just got a clock in to work on with a broken mainspring. A Hermie 351-021 marked for a 55cm pendulum. Anyway as I was searching for a spring I saw several of the same model movements calling for different pendulum lengths. I just became curious as to how this is. I’m assuming the parts are interchangeable so why would the pendulum lengths be different? Is the weight of the bob different? Or would it be a difference in the leader?
Thanks,
Charles K

[willofiam]

Hey Charles, even though the movement has the same model # there may be a wheel and or pinion that has a different number of teeth or leaves in the time train. It does not necessarily mean the leader or the suspension spring would be any different, though the overall pendulum length is different for keeping time according to how the gear train was designed. Imagine you want to build a clock, one of the very first things you would consider is how big the case would be, figure out the length of pendulum you want to have fitting it to the size of case and calculate the time gear train to keep time with that length of pendulum. @c.kelly wrote:

the parts are interchangeable

There are alot of parts that are interchangeable with the Hermle movement though not all.

[c.kelly]

Hi,
Thanks that makes sense but will make ordering replacement parts a bit more tricky. I started out working on watches 15 years ago and had only worked on about three clocks before 6 months ago. Now it seems that the request for clock work has exploded. I had five different clocks right before Christmas and right now I have three I’m working on with two more after I get these finished. That reminds me though I will start a new post here in a minute about what I found in two of the clocks I’m working on now.
Thanks,
Charles K

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