Update (May 2, 2017): We now offer a much faster way to create meshing involute gears, based on a scriptgenerating online calculator available at http://www.otvinta.com/instantgear.html. For more info, see our tutorial on instant gear generation at • Tutorial: How to Instantly Model Stra... .
Creating a pair of geometrically correct mating gears is not exactly a trivial task. The sides of gear teeth are not curved arbitrarily. Most reallife gears use a mathematical curve, called "involute curve" to keep the pressure vector between the teeth constant. This tutorial will teach you how to crate a pair of perfectly meshing gears using Blender in just a few minutes. It will also teach you how to animate the gears using drivers.
For more free tutorials and 3D models, and to make a donation, please visit www.otvinta.com.