Gear template generator

Some notes about gear design and this gear template generator

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.

Inside / planetary motion gears
You can also generate templates for inside gearing, such as would be used for planetary motion gears. Simply enter a negative number of teeth for one of the gears, and that gear will be an inside gear. Select a large number for the shaft diameter when making a template to get a circle around the gear.

Rack and pinion gearing
You can also generate rack and pinion gears. Just enter zero for the number of teeth of a gear, and the program will draw a straight gear rack instead of a gear for that gear.

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

Easily Generate Spur or Helical Gears on Your Tablesaw or Scrollsaw! www.stevengarrison.com

Printing the gear templates
To print the gear template, use the 'Print' button, rather than just printing the web page from the browser. The print button tells flash to print just the flash contents. It gets dumped to the printer in vector form, so screen resolution is not a limiting factor. A rather cool feature of flash, I think! To get the sizes specified to be correct, its best to print a test template, and then measure the distance between the lines at the top of the image, and enter that under "page width". Subsequent printouts should be scaled so that the millimeters are exact.

For gears larger than a sheet of paper, the gear is offset from center. That way, multiple copies can be printed and pasted together to form a gear template up to 40 cm in diameter.
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.

Example plywood gears from a template

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.

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