The different kinds of bevel gear !

Bevel gears are classified in different types according to geometry:

Straight bevel gears have conical pitch surface and teeth are straight and tapering towards apex. Spiral bevel gears have curved teeth at an angle allowing tooth contact to be gradual and smooth. Zerol bevel gears are very similar to a bevel gear only exception is the teeth are curved: the ends of each tooth are coplanar with the axis, but the middle of each tooth is swept circumferentially around the gear. Zerol bevel gears can be thought of as spiral bevel gears (which also have curved teeth) but with a spiral angle of zero (so the ends of the teeth align with the axis). Hypoid bevel gears are similar to spiral bevel but the pitch surfaces are hyperbolic and not conical. Pinion can be offset above, or below,the gear centre, thus allowing larger pinion diameter, and longer life and smoother mesh, with additional ratios e.g., 6:1, 8:1, 10:1. In a limiting case of making the "bevel" surface parallel with the axis of rotation, this configuration resembles a worm drive. Hypoid gears were widely used in automobile rear axles.

https://en.wikipedia.org/wiki/Bevel_gear

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