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October 25, 2014 at 3:26 am #49285
Hi,
I have a nice french clock with the pendulum missing. It has 4.8 stamped so using the following link:
http://www.mp.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.October 25, 2014 at 6:59 am #60033Hi,
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
October 26, 2014 at 12:24 am #60034I 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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