# french clock pendulum calls

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• #49285
derekas
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Hi,
I have a nice french clock with the pendulum missing. It has 4.8 stamped so using the following link:
http://www.m-p.co.uk/formulae/frpend.htm. its length should be 126mm.

However how do I calc the pendulums weight ??? Suppliers offer length & size of pendulum which alters the weight.
Any help much appreciated.

#60033
gerene
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Hi,

to calculate the pendulum length you need to know the number of vibrations per minute.
You can then use the following rule: L = t*t*g/pi*pi (L = t square times g divided by pi square)
where t is the time of one vibration, g is the acceleration due to gravity (9.81) and pi = 3.14
This gives you the theoritical length in metres.

De Carle gives a complete explanation (in inches) as well as a table in his book”Practical clock repairing”.

To calculate the number of vibrations you will need the teeth count of your wheel train.

Hope this helps.

Jan

#60034
arutha
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I can’t find anything that shows how to work out the weight needed for your french pendulum. I might have a “4 8” pendulum, I will take a look on Monday and if I have one I will weigh it for you. Worse case scenario you can make something up and just keep adding weight until the clock works. It should be somewhere around 2 1/2 ounces.
Paul.

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french clock pendulum calls