# EnggPedia - The Engineering Encyclopedia

Tue03282017

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# Terms Of the Spur Gear

## Pitch circle

The pitch circle is the circle representing the original cylinder which transmitted motion by friction, and its diameter the pitch circle diameter.

## Center distance

The center distance of a pair of meshing spur gears is the sum of their pitch circle radii. One of the advantages of the

involutes system is that small variations in the center distance do not affect the correct working of the gear.

The addendum is the radial height of the tooth above the pitch circle.

The addendum is the radial depth below the pitch circle.

## Clearance

The clearance is the difference between the addendum and the addendum.

## Whole depth

The whole depth of a tooth is the sum of the addendum and the addendum.

## Working depth

The working depth of the tooth is the maximum depth that the tooth extends into the tooth space of a mating gear. It is the sum of the addenda of the gear.

The addendum circle is that which contains the tops of the teeth and its diameter is the out side or blank diameter.

## Addendum or root circle

The addendum or root circle is that which contains the bottoms of the tooth space and its diameter is the root diameter

## Circular tooth thickness

Circular tooth thickness is measured on the tooth around the pitch circle, that is, it is the length of an arc.

## Circular pitch

Circular pitch is the distance from a point on one tooth to the corresponding point on the next tooth, measured around the pitch circle.

## Module

The module is the pitch circle diameter divided by the number of teeth.

## Diametrical pitch

The diametrical pitch is the number of teeth per inch of pitch circle diameter. This is a ratio.

## Pitch point

The pitch point of contact between the pitch circles of two gears in mash.

## Line of action

The line of action contact between the teeth of meshing gears takes place along a line tangential to the two base circles. This line passes through the pitch point and is called the line of action.

## Pressure angle

The pressure angle is the angle between the line of action and the common tangent to the pitch circle at the pitch point is the pressure angle.

## Tooth face

The tooth face is the surface of a tooth above the pitch circle, parallel to the axis of the gear.

## Tooth flank

The tooth flank is the tooth surface below the pitch circle, parallel to the axis of the gear. If any part of the flank extends inside the base circle it cannot have in volute form. It may have another form, which does not inter face with mating teeth and the usually a straight radial line.

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