[sanddrag]

You can make one tooth profile and then revolve it around in the sketch. Real gears have an involute curve on the tooth, but you can approximate it with an average radius. However, your best bet is getting ones someone else made, even though they probably don't have involute curves either. It's hard to make a drawing good enough to cut gears from (because of the involute) but the constant radius should be just fine for an inventor model.