Gear template generatorAlso available in Spanish
Some notes about gear design and this gear template generatorThis template generator is intended for generating paper templates for cutting low precision gears from plywood, phenolic, or other suitable materials with a band saw.
This gear template generator generates shapes for involute spur gears. Involute spur gears have involute shaped teeth. The best way to explain how the involute is formed is to select two gears, and check the "show line of contact" checkbox. The red line will show the line of tooth contact for the given gears, as well as the base circles. The gears work as though a string was unwound from the right gear's base circle, and wound onto the other base circle. A point on the string essentially traces the involute of the teeth. Note that the teeth always make contact along the red line, and exactly perpendicular to the line. The angle of this line with respect to vertical is the pressure angle ('Tooth angle' field in the form above)
The gear tooth generation is not perfect. Normally, one rounds the tips of gear teeth a little bit, which this program doesn't do. Also, for gears with less than about 10 teeth, and low tooth angles, its necessary to make the teeth quite narrow at the bottom (undercut), or to alter the geometry (profile shifts). So some combinations with gears of small numbers of teeth may overlap, or jam if they were real. You can check to see if the gears would overlap by selecting the 'animate' and 'two gears' checkboxes for your gears and watching them turn. My non-free gear program will automatically calculate the necessary undercut to make the gears mesh.
Ring gear / planetary motion gears
Rack and pinion gearing
There are some excellent notes on gear undercut and other design issues for small gears here on the web.
The involute shape of gears is very important for gears that run at high speed. However, for wooden gears, it really doesn't matter very much. Even if you don't cut the gears with an involute shape, the template generator is still useful as a form of protractor using the "dividing plate mode" for dividing the circle into even intervals. For an example of a different method of cutting gears, see my Wooden gear cutting jig
Printing the gear templates
My downloadable gear generator program that I have for sale doesn't need the scale calibration, and can paginate across many pages for larger gears.
I recommend ink jet printers over laser printers for printing gear templates. The fine colour registration requirements of ink jet print heads forces the printer makers to make sure that the image is not stretched or compressed in either direction. With laser printers, a stretch does not cause registration problems, so some laser printer output is sometimes stretched by as much as a percent in one axis. Its best to check that the diameter is consistent along the vertical, horizontal, and diagonal to be sure there is no distortion.
I also used my gear template generator for the gears of my screw advance box joint jig
Also check out my Wood gear cutting jig. I have to admit though that I have not used this jig since writing this gear template generator.