HINTS ON SELECTING A REPLACEMENT PLATFORM

Escape Wheel Pinion Count
Modern escapements are supplied with 8 leaf pinions. Other counts are available but as they are not interchangeable the platform and pinion must be ordered together. We cannot give a refund on the 8 leaf escape wheel originally fitted.
Replacement platforms have a frequency of 18,000 vibrations per hour and the escape wheels have 15 teeth. As there are two vibrations of the balance for each tooth, then it follows that the escape wheel must rotate 600 times per hour. That is: (18,000 divided by (15 x 2)). The centre wheel (to which the minute hand is directly attached) clearly rotates once per hour, so the gearing in between must have an overall ratio of 600:1.

To calculate the number of leaves that the pinion should have to give a ratio of 600:1, count the number of teeth on wheels A, C & E. Count the teeth on pinions B & D.The number of teeth on the escape wheel pinion is (A x C x E) / (B x D x 600)
You can count the number of leaves on the existing platform escape wheel if this is available, but it does not always follow that the natural frequency was 18,000. In the majority of cases this is so.

The answer given may not be a whole number, and you should select the escape wheel with the nearest number of teeth. The fractional difference can normally be made up for by adjusting the index lever. We show the real number so you can estimate how much adjustment will be needed.

If an impossible answer is returned, such as 3, 4 or 11 etc, then an 18,000 platform is unsuitable without major adjustments to the balance spring or replacing a wheel with one of a different tooth count.

Enter the tooth counts as shown in the ilustration

Minute wheel teeth
Second wheel pinion leaves
Second wheel teeth
Third wheel pinion leaves
Escape or contrate wheel teeth