The following four systems of gear teeth are used to manufacture gears.
1: 14 1/2 degree composite system.
2: 14 1/2 degree full depth involute system.
3: 20 degree full depth involute system.
4: 20 degree stub involute system.
The # 1: system is used for general purpose gears.
It is stronger and has no interchange ability.
The tooth profile of this system has cycloid curve at the top and bottom and involute curve at the middle portion. The teeth are produced by form cutters on milling and by hobs on hobbing machine.
The tooth profile of the 14 1/2 degree full depth involute system was developed for use with gear hobs for spur and helical gears. The tooth profile of 20 degree full depth involute system may be cut by using hobs on hobbing machine.
The increase of pressure angle from 14 1.2 degree to 20 degree cause to make the gear teeth strong.
The gear tooth in service acts as a beam and is wider at the base.
The 20 degree stub involute system has a strong tooth to transmit heavy loads.
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