GEAR DETAILS

The gears above are known as spur gears . The circle marked in red shows the outer limit of the teeth whilst the green circles are known as the pitch circles . The pitch circle of a gear is very important as it is used by engineers to determine the shape of the teeth and the ratio between gears (ratios will be explained later).

The pitch of a gear is the distance between any point on one tooth and the same point on the next tooth.

The root is the bottom part of a gear wheel.

The pitch point is the point where gear teeth actually make contact with each other as they rotate.

GEARS AND GEAR SYSTEMS

COMPOUND GEARS

Compound gears are used in engines, workshop machines and in many other mechanical devices.

In the diagram, gear ‘A' is actually two gears attached to each other and they rotate around the same centre. Sometimes compound gears are used so that the final gear in a gear train rotates at the correct speed.