TO CALCULATE THE WHEEL COUNT AND FIND THE EFFECTIVE LENGTH OF A PENDULUM
A spreadsheet to perform the calculations below is available. To download the spreadsheet click Pendulum Spreadsheet
If you find the beat for a clock without a pendulum it is possible to calculate its length by proportion to a second’s pendulum which is 39.14 inches.
To do this follow the steps below.
Count the number of teeth on Centre, Third and Escape wheels. Count the number of teeth on Third wheel and Escape wheel pinions. Put the figures into the formula below.
Z = 3600 X Number of pinion leaves in third X escape
Number of teeth in centre wheel X third X escape X 2
Note
The multiplier 2 is because there are two pallets on the escapement.
3600 is the number of beats in an hour for a second’s pendulum which is 39.14 inches long.
Effective Length = Z2 X 39.14 inches, to get millimetres multiply by 25.4.
Note
The effective length is from the bend of the suspension to one third down the pendulum bob. The rest of the length is assessed by adding 2/3 diameter of the bob and the rating nut plus the threaded length.
Here is a worked example
3600 X 8 X 8 = 0.5
96 X 80 X 30 X 2
39.14 X 0.5 X 0.5 = 9.785 inches
9.785 X 25.4 = 248.5mm