# BEVEL GEAR

The bevel gear are used to transmit power between two intersecting shafts . There are two common types of bevel gear - straight and spiral .The element of the teeth of straight bevel gear are straight lines . which converge into a common apex point .The element of the teeth of the spiral bevel gears are spiral curves which also converge into a common apex point . Involute profile is used for the form of the teeth for both types of gears . Straight bevel gears are easy to design and manufacture and give reasonably good service when properly mounted on shafts . However , they create noise at high-speed conditions .Spiral bevel gears on the other hand are difficult to design and costly to manufacture .for they require specialized and sophisticated machinery for their manufacturing .Spiral bevel gears have smooth  teeth engagement .which result in quiet operation even at high speeds .They have better strength and are thus used for high-speed . They have better strength and are thus used for high speed high power transmission .

TERMINOLOGY OF BEVEL GEAR

A bevel gear is in the form of the frustum of a cone . The dimensions of bevel gear are illustrated .Following terms are important in design of bevel gears ;
1. Pitch cone - Pitch cone is an imaginary cone , the surface of which contains the pitch lines of all teeth in the bevel gear .

2. Cone center -  The apex of pitch cone is called cone center .It is denoted by 0.

3. Cone distance -  Cone distance is the length -cone element .It is also called pitch-cone radius .It is denoted by A
O

4. Pitch Angle - The angle that the pitch line makes with the axis of the gear is called the pitch angle .It is denoted by λ .The pitch angle is also called center angle .

5. Addendum Angle - It is the angle subtended by addendum at the cone center .It is denoted by α .

6. Dedendum Angle - It is the angle subtended by dedendum at the cone center .It is denoted by delta .

7. Face angle - It is the angle subtended by the face of the tooth at the cone center .

8. Root angle - It is angle subtended by the root of the tooth at the cone center .

9. Back bone - The back cone is an imaginary cone and its elements are perpendicular to the element of the pitch cone .

10. Back cone Distance - It is the length of back cone element .It is also called back cone radius .