Wednesday, February 27, 2008

Systems of Gear Teeth

The following four systems of gear teeth are commonly used in practice :
1. 14½o Composite system,
2. 14 ½o Full depth involute system,
3. 20o Full depth involute system, and
4. 20o Stub involute system.

The 14½o composite system is used for general purpose gears. It is stronger but has no interchangeability. The tooth profile of this system has cycloidal curves at the top and bottom and involute curve at the middle portion. The teeth are produced by formed milling cutters or hobs. The tooth profile of the 14½o full depth involute system was developed for use with gear hobs for spur and helical gears.
The tooth profile of the 20o full depth involute system may be cut by hobs. The increase of the pressure angle from 14½o to 20o results in a stronger tooth, because the tooth acting as a beam is wider at the base. The 20o stub involute system has a strong tooth to take heavy loads.

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