2. Introduction
Gears are machine elements, which are used for power transmission between
shafts, separated by small distance.
Irrespective of the type, each gear is provided with projections called teeth and
intermediate depressions called tooth spaces.
The drive is positive and when one gear rotates, the other also rotates;
transmitting power from one shaft to the other.
3. Types of Gears
• Gears are classified on the basis of the shape of the tooth profile and the
relative position of the shafts between which, power transmission takes place.
The pictorial views of some of the most commonly used gear trains, are shown
5. Gears and Gearing
Spur Gear
Spur gears, illustrated in Fig., have teeth parallel to the axis of rotation and are used to
transmit motion from one shaft to another, parallel, shaft.
6. Spur Gearing
In all gearings except worm gearing, the smaller of the two gears is called the
pinion and the larger one, the gear or gear wheel.
7. Helical gears
• Helical gears have teeth inclined to the axis of rotation at an angle, known as helix angle.
These are also used to connect parallel shafts.
• When helical gears are used, the shaft bearings are subjected to thrust loads which may be
resisted by using a double helical gear (herring-bone gear).
• Helical gearing is noiseless in operation because of the more gradual engagement of the
teeth during meshing.
9. Bevel Gears
• In bevel gears, the teeth are formed on conical surfaces and are used for transmitting power
between intersecting shafts.
Bevel Gearing
10. Warm and Warm Gearing
Worm and worm gear in combination, i.e., in meshing is known as worm gearing and is
used in speed reducers requiring large reductions.
11. Assignment-9
A gears have 30 teeth of involute profile, pitch circle diameter of 180mm/90mm and
pressure angle of 20°. Draw the profile of four complete teeth for the gear and
pinion in mesh.
