# 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 Terminology:

1. Addendum:The radial distance between the Pitch Circle and the top of the teeth.
2. Arc of Action: Is the arc of the Pitch Circle between the beginning and the end of the
engagement of a given pair of teeth.
3. Arc of Approach: Is the arc of the Pitch Circle between the first point of contact of the gear
teeth and the Pitch Point.
4. Arc of Recession: That arc of the Pitch Circle between the Pitch Point and the last point of
contact of the gear teeth.
5. Backlash: Play between mating teeth.
6. Base Circle: The circle from which is generated the involute curve upon which the tooth profile is based.
7. Center Distance: The distance between centers of two gears.
8. Chordal Addendum: The distance between a chord, passing through the points where the Pitch Circle crosses the tooth profile, and the tooth top.
9. Chordal Thickness: The thickness of the tooth measured along a chord passing through the points where the Pitch Circle crosses the tooth profile.
10. Circular Pitch: Millimeter of Pitch Circle circumference per tooth.
11. Circular Thickness: The thickness of the tooth measured along an arc following the Pitch Circle.
12. Clearance: The distance between the top of a tooth and the bottom of the space into which it fits on the meshing gear.
13. Contact Ratio: The ratio of the length of the Arc of Action to the Circular Pitch.
14. Dedendum: The radial distance between the bottom of the tooth to pitch circle.
15. Diametral Pitch: Teeth per mm of diameter.
16. Face: The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.
17. Face Width: The width of the tooth measured parallel to the gear axis.
18. Flank: The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth
19. Wheel:Larger of the two meshing gears is called wheel.
20. Pinion: The smaller of the two meshing gears is called pinion.
21. Land: The top surface of the tooth.
22. Line of Action: That line along which the point of contact between gear teeth travels, between the first point of contact and the last.
23. Module: Ratio of Pitch Diameter to the number of teeth.
24. Pitch Circle: The circle, the radius of which is equal to the distance from the center of the gear to the pitch point.
25. Diametral pitch: Ratio of the number of teeth to the of pitch circle diameter.
26. Pitch Point: The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crosses the pitch circles.
27. Pressure Angle: Angle between the Line of Action and a line perpendicular to the Line of Centers.
28. Profile Shift: 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.
29. Ratio: Ratio of the numbers of teeth on mating gears.
30. Root Circle: The circle that passes through the bottom of the tooth spaces.
31. Root Diameter: The diameter of the Root Circle.
32. Working Depth: The depth to which a tooth extends into the space between teeth on the mating gear.

##### Mechanical Subjectwise Basic Concept Notes ,Articles

Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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