One of the more tedious jobs in clock repair is counting the number of teeth on the wheels in order to calculate the correct running rate for a movement. If you have a lathe, MicroSet can make this job much easier. The picture below shows a setup that can be used on a Sherline lathe. If you don't have a Sherline lathe you can adapt this concept to whatever lathe you have.
The wheel to be counted is placed in the lathe chuck. Acquire a strip of thin brass from a hardware store that's about 1/4" wide and thin enough to flex very easily. I used .016" thickness. Mount the brass strip on top of the lathe cutting tool so it extends about two inches. Reverse the cutting tool and pull it back so it doesn't protrude from the front of the tool holder. Advance the tool holder until the brass strip reaches into the valley betweeen two teeth.
Clip the MicroSet acoustic sensor onto the brass strip in front of the tool holder. Arrange the sensor and cable so they won't move around as you work. Such movement may introduce errors in the count.
Put a mark on the wheel so you can identify the starting and ending position. Turn the lathe headstock slowly by hand in a clockwise direction. The brass strip will rise up and click over each tooth tip. The acoustic sensor will hear this click. Put MicroSet into the Count Mode, and it will count each tooth as you rotate the wheel. Watch your mark, and when you get back to the starting point, MicroSet will tell you how many teeth are on the wheel.
If you have the Rate Finder option for your MicroSet, it will be even easier to count teeth. Fasten a magnet to some part of the headstock that rotates. Mount the magnetic sensor so it will trigger each time the magnet goes around. Now you can use the Rate Finder mode to count teeth and you don't have to watch for a mark on the wheel --- the magnetic sensor does that for you.
The Rate Finder displays results as "Beats Per Hour". In this case, the value will be the number of teeth on the wheel. The Rate Finder also shows you how many measurements have been taken. For example, it might say:
This would mean that you've rotated the wheel four times and, on average, 72 teeth were counted on each rotation. Keep an eye on the display as you turn the headstock. If MicroSet shows you the same value for each rotation, you can have confidence that the value is correct. If you get a value that changes, or if you get a fraction (like 72.25) you know that a miscount has occurred in one of the rotations.
Here are a few more considerations to get things to work properly.
Santa Barbara, California
June 17, 2004