# EnggPedia - The Engineering Encyclopedia

Wed04162014

Last update06:04:15 AM

Cpanel

# Gear Definition, Types of Gear

## Definition

Gear is a cylinder, wheel, or disk on the surface of which are cut parallel teeth. The larger gear is called the gear the smaller, the pinion. Usually when two gears in mesh and one is larger than the other is, the names gear pinion is are replied. Spur gear is used to transmit power from one shaft to another in cases where those shafts have their axis parallel.

## Types of gear

The following are the types of the gear:

### 1-Bevel gear:

These gears have teeth cut on a cone instead of a cylinder blank. They are used in pairs to transmit rotary motion and torque where the bevel gear shafts are at right angles (90 degree) to each other.

### 2-Crossed helical gear

These gears also transmit rotary motion and torque through a right angle. The teeth of a helical gear are inclined at an angle to the axis of rotation of the gear.

### 3-Worm and worm wheel

A gear which has one tooth is called worm. The tooth is in the form of a screw thread. A worm wheel meshes with the worm. The worm wheel is a helical gear with teeth inclined to that they can engage with the tread like worm. Like the cross helical gears, the worm and the worm wheel transmit torque and rotary motion through a right angle. The worm always drives the worm wheel and never the other way round. The mechanism locks if the worm wheel tries to drive the worm. Worm mechanism is very quiet running.

### 4-Helical gear

The gear is used for application that requires very quite and smooth running, at high rotational velocities. Parallel helical gears have their teeth inclined at a small angle to their axis of rotation. Each tooth is part of a spiral or helix. The helical gears have splines cut in their center holes. The gear can move along a splined shaft, although they rotate with the shaft. Double helical gears give an efficient transfer of torque and smooth motion at very high rotational velocities.

### 5-Spiral bevel gears

When it is necessary to transmit quietly and smoothly a large torque through a right angle at high velocities, spiral bevel gears can be used. Spiral bevel gears have teeth cut in helix spiral form on the surface of a cone. They are quieter running than straight bevel gears and have a longer life. Spiral bevel gears are used in motorcar axle gearboxes.

### 6-Internal gears

It is possible to cut gear teeth on the face of a gear wheel. Also, gear teeth can be cut the inclined of a gear ring. Internal gears have better load carrying capacity than external spur gear. They are safer in use because the teeth are guarded.

### 7-Rack and pinion

A rack and pinion mechanism is used to transform rotary motion in to linear motion and vice versa. A round a spur gear, the pinion, meshes with a spur gear which has teeth set in a straight line, the rack. The rack and pinion can transform rotary motion into linear motion and vice versa in three ways.

• Rotation of the pinion about a fixed center causes the rack to move in a straight line.
• Movement of the rack in a straight line causes the pinion to rotate about a fixed center.
• If the rack is fixed and the pinion rotates, then the pinion’s center moves in a straight line taking the pinion with it.

### 8-Spur gear

A spur gear is one of the most important ways of transmitting a positive motion between two shafts lying parallel to each other. A gear of this class may be likened to a cylindrical blank which has a series of equally spaced in the grooves around its perimeter so that the projections on one blank may mesh in the grooves of the second. As the design should be such that the teeth in the respective gears are always in mesh the revolutions made by each is definite, regular and in the inverse ratio to the numbers of teeth in the respective gears. This ability of a pair of well made spur gears to give smooth, regular, and positive drive is of the greatest importance in many engineering designs.