Constructing Involute Gear Profiles

Thu, 8 Mar 2012

As promised in yesterday's blog, a post about the construction of involute gears. The profile of the side of an involute gear is defined mathematically but you can also construct it with a few household items. Simply put, it is the curve you get as you unwrap a string from around a cylinder.

Starting with a piece of string fixed by one end to a cylinder I've created an involute curve using a fine pen.  

Following round the cylinder both faces of each teeth are constructed and joined to the next. With small gears, each face is quite markedly curved.

The larger the gear, the higher the number of teeth and the straighter the sides of the teeth become.

Luckily I don't need to use this string and cylinder technique to construct gear profiles for my models, instead I've been using the gear profile creator on this site. Thank you The Internets!