Excel files to help you design Gear Trains for wooden clocks

Spreadsheet to calculate the length of clock pendulums

If you have decided to design and build your own wooden clock then the following charts should give you some idea of how to tackle the tricky mathematical bits that are needed to make sure that the clock can run accurately throughout the day. Some of my earlier posts should have introduced you to some of these formulae that are used in this process. The idea here though is that we try to automate the process using Excel to do the heavy lifting and at the same time give you the opportunity to try out different combinations needed to me the constraints of the design you have in your head.

This first chart is used to calculate the length of the clock's pendulum which in turn uses various combinations of gears to achieve this, with you inputting tooth numbers into the appropriate box.

Basic concepts

• Minute shaft makes 1 revolution every 3600 seconds
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• You are using a Graham Escapement that stops the rotation 2x for each completed swing(Tic Toc)
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• metric units
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• g= 9.8m/s/s
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• T= pendulum period of time for a Tick and A Tock
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• pi= 3.14159
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• length of pendulum = g(T/(2 *pi))2
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• If you aim to have a second hand then the Escapement wheel should rotate once in 60 secs.

The chart provides inputs for a maximum of 3-wheeled Gear Train and if you only use 2 then fill the appropriate boxes with the number 1, it also requires you to provide a pair of gears with a Wheel and a Pinion for each pairing. You must only input figures into the Green coloured boxes as the orange ones contain the Formulae to calculate the value.
If you want to add other combinations to the green area either clear an unwanted row or use the normal Excel technique to copy the whole Green and Orange bottom row of boxes and paste them to the row below.

Click on the picture below to download the Excel File.

Spreadsheet to calculate Gear tooth Profile.

I have always used a modified version of the standard gear tooth profile so as to give me more clearance between teeth and a bit more leeway when cutting the teeth by hand or on a scroll saw. The most important thing with regards to tooth profile is consistency in the pitching of the teeth. The charts below reflect this and the details are given for both the large gear and the Pinions in the most used tooth sizes.

Again if you want to add other combinations to the green area either clear an unwanted row or use the normal Excel technique to copy the whole Green and Orange bottom row of boxes and paste them to the row below.

Click on the picture below to download the Excel File.

PCD is the Number of TeethX Mod

Outside Diameter is (Number of teeth + 2)X Mod

Root Diameter PCD-(ModX3)

Spreadsheet to calculate centre distance between a Pair of Gears

This is probably the simplest of the charts as it simply calculates the distance between the two mating gears by adding the two Pitch Circle Diameters (Ø50 mm in this case) together and dividing by 2. If you experience difficulty with distortion of the gears that causes problems with assembly then you might want to increase this by 0.5 mm.