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Gearing Systems : Undercutting

If the dedendum of a gear tooth is large enough to extend below base circle interference will most likely occur between the two mating gears, which will cause the tip of one tooth to start to cut away material from the other tooth's root. This is known as undercutting.

Undercutting should be avoided due to the fact that tooth that has material removed from its root will become weaker. This could severely lower that tooth's maximum moment and shear force, increasing the chances that the tooth could fail at a much lower load than expected.

A way to avoid undercutting is to avoid gears that have too few teeth. When a gear has a large number of teeth, those teeth will be comparably smaller in comparison to the actual diameter of the gear lowering the chances of undercutting. While as the number of teeth are reduced on a gear, the dedendum of the tooth will increase in length until undercutting occurs.


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