Fig. 4.2. Spur Gear and Pinion pair
Terms used in Gear
Addendum: The radial distance between the Pitch Circle and the top of the teeth.
Dedendum: The radial distance between the bottom of the tooth to pitch circle.
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 gears.
Circular Pitch: Millimeter of Pitch Circle circumference per tooth.
Circular Thickness: The thickness of the tooth measured along an arc following the Pitch Circle
Clearance: The distance between the top of a tooth and the bottom of the space into which it fits on themeshing gear.
Contact Ratio: The ratio of the length of the Arc of Action to the Circular Pitch.
Diametral Pitch: Teeth per mm of diameter.
Face: The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.
Face Width: The width of the tooth measured parallel to the gear axis.
Flank: The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth
Gear: The larger of two meshed gears. If both gears are the same size, they are both called “gears”.
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 ofcontact and the last.
Module: Millimeter of Pitch Diameter to Teeth.
Pinion: The smaller of two meshed gears.
Pitch Circle: The circle, the radius of which is equal to the distance from the center of the gear to the pitchpoint.
Diametral pitch: Teeth per millimeter of pitch diameter.
Pitch Point: The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crossesthe 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.
Working Depth: The depth to which a tooth extends into the space between teeth on the mating gear.
