# Gear Terminology: Basic Definition Used in Gear

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Today we will discuss about gear terminology. Gears are widely used in mechanical industries for power transmission. It is used where small distance between driver and driven shaft.  It is the only positive drive which can transfer exact velocity ratio to the driven shaft, that’s why it is widely used in various machines and other mechanical devices. Gear terminology means all definitions used to describe a gear or the terms used to design a gear. The most common definitions are described below.

## Gear Terminology:

The following terms, which are mostly used to describe a gear, are as follow.

#### Face of tooth:

It is defined as the surface of the tooth above the pitch circle is known as face.

#### Flank of tooth:

The surface of the tooth below the pitch circle is known as flank.

#### Top land:

The top most surface of the tooth is known as the top land of the tooth.

#### Face width:

Width of the tooth is known as face width.

#### Pitch Circle:

It is an imaginary circle which is in pure rolling action. The motion of the gear is describe by the pitch circle motion.

#### Pitch Circle diameter:

The diameter of the pitch circle from the center of the gear is known as pitch circle diameter. The gear diameter is described by its pitch circle diameter.

#### Pitch point:

When the two gears are in contact, the common point of both of pitch circle of meshing gears is known as pitch point.

#### Pressure angle or angle of obliquity:

Pressure angle is the angle between common normal to the pitch circle to the common tangent to the pitch point.

Distance between the pitch circle to the top of the tooth in radial direction is known as addendum.

#### Dedendum:

Distance between the pitch circle to the bottom of the tooth in radial direction, is known as dedendum of the gear.

The circle passes from the top of the tooth is known as addendum circle. This circle is concentric with pitch circle.

#### Dedendum circle:

The circle passes from the bottom of the tooth is known as dedendum circle. This circle is also concentric with pitch circle and addendum circle.

#### Circular pitch:

The distance between a point of a tooth to the same point of the adjacent tooth, measured along circumference of the pitch circle is known as circular pitch. It is plays measure role in gear meshing. Two gears will mesh together correctly if and only they have same circular pitch.

#### Diametrical pitch:

The ratio of the number of teeth to the diameter of pitch circle in millimeter is known as diametrical pitch.

#### Module:

The ratio of the pitch circle diameter in millimeters to the total number of teeth is known as module. It is reciprocal of the diametrical pitch.

#### Clearance:

When two gears are in meshing condition, the radial distance from top of a tooth of one gear to the bottom of the tooth of another gear is known as clearance. The circle passes from the top of the tooth in meshing condition is known as clearance angle.

#### Total depth:

The sum of the addendum and dedendum of a gear is known as total depth. It is the distance between addendum circle to the dedendum circle measure along radial direction.

#### Working depth:

The distance between addendum circle to the clearance circle measured along radial direction is known as working depth of the gear.

#### Tooth thickness:

Distance of the tooth measured along the circumference of the pitch circle is known as tooth thickness.

#### Tooth space:

Distance between the two adjacent tooth measured along the circumference of the pitch circle is known as the tooth space.

#### Backlash:

It is the difference between the tooth thickness and the tooth space. It prevents jamming of the gears in meshing condition.

#### Profile:

It is the curved formed by the face and flank is known as profile of the tooth. Gear tooth are generally have cycloidal or involute profile.

#### Path of contact:

The curved traced by the point of contact of two teeth form beginning to the end of engagement is known as path of contact.

#### Arc of contact:

It is the curve traced by the pitch point form the beginning to the end of engagement is known as arc of contact.

#### Arc of approach:

The portion of the path of contact from beginning of engagement to the pitch point is known as arc of approach.

#### Arc of recess:

The portion of the path of contact form pitch point to the end of the engagement is known as arc of recess.

Today we have learned about Gear terminology or the basic term used to design a gear. If you have any query regarding this article, ask by commenting below. Subscribe our website for more informative articles. Thanks for reading it.

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