Gear terminology






Gear Terminology:

Gear: The larger of two meshed gears. If both gears are the same size, they are both called “gears”.

Pinion: The smaller of two meshed gears.

Face: The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.

Flank: The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth

Addendum: The radial distance between the Pitch Circle and the top of the teeth.

Dedendum: The radial distance between the bottoms of the tooth and the pitch circle.

Module: Millimeter of Pitch circle Diameter to Teeth.

Backlash: Play between mating teeth.

Base Circle: The circle from which is generated the involute curve upon which the tooth profile is based.

Center Distance: The distance between centers of two meshing gears.

Circular Pitch: Distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth.

Tooth Thickness: The thickness of the tooth measured along an arc following the Pitch Circle

Clearance: The distance between the clearance circle and Dedendum circle.

Diametral Pitch: It is the ratio of number of teeth to the pitch circle diameter in millimeter.

Face Width: The width of the tooth measured parallel to the gear axis.

Top land: The top surface of the tooth.

Line of Action: That line along which the point of contact between gear teeth travels, between the first point of contact and the last.

Pitch Circle: The circle, the radius of which is equal to the distance from the center of the gear to the pitch point.

Pitch Point: The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crosses the pitch circles.

Pressure Angle: Angle between the Line of Action and a line perpendicular to the Line of Centers.

Root Circle: The circle that passes through the bottom of the tooth spaces.

Root Diameter: The diameter of the Root Circle.

Working Depth: The depth to which a tooth extends into the space between teeth on the mating gear.