When shafts are intersecting at 90°, then, which of the following gears are recommended for transmission of power? 

Explanation:

Bevel Gear: 

• Bevel gears are used to transmit motion between shafts at various angles to each other.
• Connecting shafts are at 90°.
• The teeth profile may be straight or spiral.

Spur Gear: 

• The teeth are cut parallel to the axis of rotation. 
• The spur gears are used to transmit power between two parallel shafts.

Helical Gear: 

• In a helical gear, the teeth are cut at an angle to the axis of rotation.
• It is used to transmit power between two parallel shafts.
• The end thrust is exerted by the driving and driven gears in the case of helical gears and the thrust may be eliminated by using double helical gears. These gears are called herring-bone gears.

Mitre gear: 

• If two bevel gears are symmetrical to each other and transmit motion at right angles, such gears may be called ‘mitre gears’.

Worm shaft and worm gear: 

• The worm shaft has spiral teeth cut on the shaft and worm wheel is a special form of gear teeth cut to mesh with the worm shaft.
• These are widely used for speed reduction purpose.

Rack and pinion: 

• The rack and pinion can change rotary into linear movement and vice versa.