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)

• Gear Ratio

• Addendum

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.

• Fillet radius

 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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