# Basic Of Gears -Gear Terminology/ Gear nomenclature

## Basic Of Gears -Gear Terminology/ Gear nomenclature

__Gears:__**Introduction:**

The slip and creep in the belt or rope drives is a common phenomenon, in the transmission of motion or power between two shafts. The effect of slip is to reduce the velocity ratio of the drive. In precision machine, in which a definite velocity ratio is importance (as in watch mechanism, special purpose machines..etc), the only positive drive is by means of gears or toothed wheels.

Gear nomenclature |

__Gear Terminology:__The radial distance between the Pitch Circle and the top of the teeth.__Addendum:__Is the arc of the Pitch Circle between the beginning and the end of the__Arc of Action:__

engagement of a given pair of teeth.Is the arc of the Pitch Circle between the first point of contact of the gear__Arc of Approach:__

teeth and the Pitch Point.That arc of the Pitch Circle between the Pitch Point and the last point of__Arc of Recession:__

contact of the gear teeth.Play between mating teeth.__Backlash:__The circle from which is generated the involute curve upon which the tooth profile is based.__Base Circle:__The distance between centers of two gears.__Center Distance:__The distance between a chord, passing through the points where the Pitch Circle crosses the tooth profile, and the tooth top.__Chordal Addendum:__The thickness of the tooth measured along a chord passing through the points where the Pitch Circle crosses the tooth profile.__Chordal Thickness:__Millimeter of Pitch Circle circumference per tooth.__Circular Pitch:__The thickness of the tooth measured along an arc following the Pitch Circle.__Circular Thickness:__The distance between the top of a tooth and the bottom of the space into which it fits on the meshing gear.__Clearance:__The ratio of the length of the Arc of Action to the Circular Pitch.__Contact Ratio:__The radial distance between the bottom of the tooth to pitch circle.__Dedendum:__Teeth per mm of diameter.__Diametral Pitch:__The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.__Face:__The width of the tooth measured parallel to the gear axis.__Face Width:__The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth__Flank:__Larger of the two meshing gears is called wheel.__Wheel:__The smaller of the two meshing gears is called pinion.__Pinion:__The top surface of the tooth.__Land:__That line along which the point of contact between gear teeth travels, between the first point of contact and the last.__Line of Action:__Ratio of Pitch Diameter to the number of teeth.__Module:__- Pitch Circle: The circle, the radius of which is equal to the distance from the center of the gear to the pitch point.
Ratio of the number of teeth to the of pitch circle diameter.__Diametral pitch:__The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crosses the pitch circles.__Pitch Point:__Angle between the Line of Action and a line perpendicular to the Line of Centers.__Pressure Angle:__An increase in the Outer Diameter and Root Diameter of a gear, introduced to lower the practical tooth number or acheive a non-standard Center Distance.__Profile Shift:__Ratio of the numbers of teeth on mating gears.__Ratio:__The circle that passes through the bottom of the tooth spaces.__Root Circle:__The diameter of the Root Circle.__Root Diameter:__The depth to which a tooth extends into the space between teeth on the mating gear.__Working Depth:__

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