1. According to position of tooth and gear surface, gears can be divided into external gears and internal gears.
2. According to shapes of gears, gears can be divided into spur gears, bevel gears, non-circular gears, racks.
3. According to shapes of gears tooth, gears can be divided into spur gears, helical gears(spiral gears), herringbone gears(double helical gears).
4. According to gear tooth profile, gears can be divided into involute gears, cycloidal gears.
7 Common Gears
1. Spiral bevel gears and Straight bevel gears
2. Hypoid gears
Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect.
3. Worm gears
Worm gears resemble screws. A worm gear is usually meshed with a spur gear or a helical gear, which is called worm wheel.
4. Epicyclic gears (Planetary gears)
5. Harmonic gears
6. Involute gears
7. Cycloid gears (Cycloidal gears)