Terminology of Gear In Gear Design

 

1.  Pitch surface : The surface of the imaginary rolling cylinder (cone, etc.) that the toothed gear may be considered to replace.
2. Pitch Circle: It is an imaginary circle on which pure rolling action would transmit the same motion of actual gear.
3.  Addendum circle: A circle bounding the ends of the teeth, in a right section of the gear. 
4. Root (or dedendum) circle: The circle bounding the spaces between the teeth, in a right section of the gear.
5. Addendum: The radial distance between the pitch circle and the addendum circle.
6. Dedendum: The radial distance between the pitch circle and the root circle.
7. Clearance: The difference between the dedendum of one gear and the addendum of the mating gear.
8. Face of a tooth: That part of the tooth surface lying outside the pitch surface.
9. Flank of a tooth: The part of the tooth surface lying inside the pitch surface.
10. Circular thickness (also called the tooth thickness) : The thickness of the tooth measured on the pitch circle. It is the length of an arc and not the length of a straight line.
11. Tooth space: The distance between adjacent teeth measured on the pitch circle.
12. Backlash: The difference between the circle thickness of one gear and the tooth space of the mating gear.
13. Circular pitch : The width of a tooth and a space, measured on the pitch circle.
14. Diametral pitch : The number of teeth of a gear per inch of its pitch diameter. A toothed gear must have an integral number of teeth. The circular pitch, therefore, equals the pitch circumference divided by the number of teeth. The diametral pitch is, define by, the number of teeth divided by the pitch diameter.