Spur Gears

General: Spur gears are the most commonly used gear type. They are characterized by teeth which are perpendicular to the face of the gear. Spur gears are by far the most commonly available, and are generally the least expensive.The basic descriptive geometry for a spur gear is shown in the figure below.

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The diametral pitch, P, is related to the number of teeth, N, and the pitch diamter, d, by the relation P=N/d. The circular pitch, p, is the width of a tooth and a space (measured along the pitch circle), and is related to the diametral pitch by Pp=PI.
Limitations: Spur gears generally cannot be used when a direction change between the two shafts is required.
Advantages:Spur gears are easy to find, inexpensive, and efficient.