# What is Gear Terminology | Definition of gear

#### Gears

Gears are toothed wheels used for transmitting motion and power from one shaft to another when they are not too for apart and when a constant velocity ratio is desired.

• #### Pitch

Pitch of two meshing gear is same. It is define as follow

1.Circular Pitch (p)  –

It is the distance measured along the circumference of the pitch circle on one tooth to the corresponding point on the adjacent tooth.

2. Diametral Pitch P   –

It is the number of teeth per unit length of the pitch circle dia. in inches.

• #### Module (m)

It is the ratio of pitch dia. in mm to the number of teeth.The term is used in S.I. units in place of diametral pitch.
m  =  d/T
• #### Gear Ratio

It is the ratio of the number of teeth on the gear to that on the pinion.
G = T/t
Where T = Number of teeth on the gear
t  = Number on teeth on the pinion

It is the radial height of a tooth above the pitch circle.

• #### Dedendum

It is the radial depth of a tooth below the pitch circle. Its standard value is 1.157m.

• #### Clearance

It’s radial difference between the addendum and the dedendum of a tooth.

• #### Backlash

It is the difference between the space width and the tooth thickness along the pitch circle.
Backlash  =   Space width  –   Tooth thickness

• #### Working Depth

It is the distance between top of addendum circle to the clearance circle.

• #### Whole Depth

It is the total depth of a tooth space.

• #### Tooth thickness

The tooth thickness is measured at the pitch diameter.

• #### Face width

It is the distance of top of the gear teeth.

or

The length of the teeth in the axial direction.

• #### Tooth face

The mating surface of a gear tooth between the addendum circle and the pitch circle.

• #### Tooth flank

The mating surface of a gear tooth measured between the pitch circle and the base circle.

It is the radius of the fillet curve at the base of the gear tooth.

• #### Backlash

Backlash is the difference between the thickness of a tooth and the width of a tooth space on which it meshes.

• #### Top land

The top land is the surface of the top of the tooth.

• #### Gear center

A gear center is the center of the pitch circle.

• #### Gear range

The gear range is difference between the highest and lowest gear ratios.

• #### Helix angle

Helix angle is the angle between the helical tooth face and an equivalent spur tooth face.

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