Quote:
Originally Posted by Tristan Lall
Is that strictly correct? I would say that doing so changes the stress distribution (because the non-meshing parts of the gear teeth will resist bending). While some stresses may well be locally slightly higher than in the same-width case (I'm thinking right at the edge of the meshing tooth), on balance, the amount of stress at a given point in the wider gear ought to be lower, thanks to the contribution of the extra material.
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When I design gears, one gear is almost always a bit wider than the other. There are two stresses to think about. The first is bending stress and the second is pitting stress. The bending stress is (or may be) different for each of the gears in the mesh. The pitting stress is the same for both gears since it is the result of how the two gears contact together. Due to the stack-up of tolerances in a gear box or transmission, there is axial error between the two gears in a mesh. In order to guarantee a given contact face width, one gear is generally made a bit wider. For bending stress, a rule of thumb is that up to 1/2 a whole depth of excess face width counts toward the gear face width and thus reduces bending stress in the wider gear.