Terms About Gears

Tooth (tooth)-each convex part of the gear used for meshing. Generally speaking, these raised parts are arranged radially. The teeth on the mating gears are in contact with each other, resulting in continuous meshing operation of the gears.

Cogging-the space between two adjacent teeth on a gear.

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End surface-the plane perpendicular to the axis of the gear or worm on the cylindrical gear or cylindrical worm.

Normal surface ─ ─ On a gear, the normal surface refers to the plane perpendicular to the tooth line of the gear.

Addendum circle-the circle where the tip of the tooth is located.

Tooth root circle-the circle where the groove bottom is located.

Base circle ─ ─ A circle on which the generating line forming the involute is purely rolling.

Index circle ─ ─ The reference circle for calculating the geometrical dimensions of the gear in the end face. For spur gears, the modulus and pressure angle on the index circle are both standard values.

Tooth surface-the side surface of the tooth between the cylindrical surface of the tooth tip and the cylindrical surface of the tooth root.

Tooth profile ─ ─ The cut line of the tooth surface by a specified curved surface (a plane for cylindrical gears).

Tooth line ─ ─ The intersection line between the tooth surface and the indexing cylindrical surface.

End tooth pitch pt──the length of the indexing arc between the tooth profiles of the two adjacent teeth on the same side.

Modulus m──The quotient obtained by dividing the tooth pitch by the pi, in millimeters.

Diameter P──The reciprocal of the modulus, measured in inches.

Tooth thickness s──the length of the indexing arc between the tooth profiles on both sides of a tooth on the end face.

Groove width e──the length of the indexing arc between the tooth profiles on both sides of a tooth groove on the end face.

Addendum height hɑ──The radial distance between the addendum circle and the index circle.

Tooth root height hf──The radial distance between the index circle and the tooth root circle.

Full tooth height h──The radial distance between the addendum circle and the root circle.

Tooth width b──The size of the gear teeth along the axial direction.

End face pressure angle ɑt── The acute angle between the radial line passing the intersection of the end face tooth profile and the index circle and the tangent line of the tooth profile passing this point.

Standard Rack: Only the dimensions of the base circle, tooth profile, full tooth height, crown height, and tooth thickness are all racks that conform to the standard spur gear specifications, and are cut according to the standard gear specifications. It is called the reference rack.

Standard Pitch Circle: It is used to determine the reference circle of each part of the gear. It is the number of teeth x modulus

Standard Pitch Line: A specific pitch line on the rack or the tooth thickness measured along this line, which is one-half of the pitch.

Action Pitch Circle: When a pair of spur gears bite together, each has a tangent to make a rolling circle.

Standard Pitch (Standard Pitch): The selected standard pitch is used as the benchmark, which is equal to the reference rack pitch.

Pitch Circle: The trajectory left on each gear at the occlusal contact point on the connecting center line of the two gears is called the pitch circle.

Pitch Diameter: The diameter of the pitch circle.

Effective tooth height (Working Depth): the crown height of a pair of spur gears. Also known as the working tooth height.

Addendum: The difference between the addendum circle and the pitch circle radius.

Backlash: The gap between the tooth surface and the tooth surface when the two teeth are engaged.

Clearance: When two teeth are engaged, the gap between the tip circle of one gear and the bottom of the other gear.

Pitch Point: The tangent point between a pair of gears and the pitch circle.

Pitch: The arc distance of the corresponding points between two adjacent teeth.

Normal Pitch: The pitch measured by the involute gear along the same vertical line of a specific section.

Transmission ratio (): The ratio of the speed of the meshing two gears. The speed of the gear is inversely proportional to the number of teeth. Generally, n1 and n2 represent the speed of the two meshing teeth.