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Originally Posted by Clark Gilbert
Heck with drawing gears all together. I guess you could bother with it when working on models for animation in 3d Studio Max or something. One thing I picked up from reading countless CAD prints from Andy Baker was that his gears were always just cylinders. This keeps unnecessary lines off your CAD prints and makes orthographic views and section views more visually pleasing. If you are making a 3d model to show off it will also be easier on your computer since it wont have to process all the teeth and faces. Even when making individual prints of just the gear keep the teeth off and make a note saying something like "Altered purchased gear."
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This works for standard gears. But when you need say a 12 pitch 30 deg pressure angle 15 tooth gear, then you're kind of out of luck. You really do need to model the gear, teeth and all. Especially of you're using a rapid prototyping machine to make the real one
Fortunately this is pretty rare, but it does happen. One simplification I have used is to make a cylinder with diameter= Pitch Diameter-Dedendum and then make a trapezoid on the edge that has a height of addendum+dedendum and whose top is an arc covering the angle 360/(3*N). The bottom is twice that. This gives a pretty good looking gear without it getting huge in terms of file size. It also makes it easy to check and make sure you don't have problems with center distances etc. Of course you don't have to do the whole gear for that, just the section making contact.