The Short Answer
A spiral bevel gear is a cone-shaped gear with curved, slanted teeth. It is used in pairs to transmit power between two shafts whose axes meet, usually at 90 degrees.
How it Differs from Other Gears
A spur gear connects parallel shafts. A bevel gear connects shafts that meet at an angle. In a straight bevel gear the teeth are straight and meet along their whole length at the same moment, which gives a knock each time a tooth enters mesh. In a spiral bevel gear the teeth are curved, so contact starts at one end of the tooth and sweeps across it. That gradual contact is quieter and spreads the load.
Parts of a Set
A spiral bevel set has a pinion, the smaller gear, and a gear, also called the crown wheel or ring gear. Both are cut and finished together as a matched pair. The pinion and the gear must have opposite hands of spiral: a left-hand pinion works with a right-hand gear.
Advantages
More teeth in contact at the same time, so a higher load capacity. Smoother, quieter running. Better performance at high speed. The price for this is a more complex tooth shape, a need for accurate mounting, and an axial thrust that the bearings must carry.
Where They Are Used
Industrial gearboxes, rolling mills, crushers, conveyors, machine tools, marine drives and many other machines. See the spiral bevel gear product page, and the guide on spiral bevel and straight bevel gears.
