Key | Functions, Types, Advantages, Disadvantages

By | March 10, 2019

What is Key?

A key is a machine element which is used to connect a shaft to other machine elements like Gears, Pullies, Couplings, Sprockets or Flywheels.

Functions of the key

There are two basic functions of key

  1. Transmit torque to hub and vice versa
  2. Prevent relative motion of the shaft and the joined machine element

Types of keys

Keys can be classified on the basis of following factors like.

  1. Cost
  2. Rigidity of connection
  3. Tightness of fit
  4. Power to be transmitted

On the basis of above factors, we have following types of keys

  1. Key with and without Gib head
  2. Parallel key and taper key
  3. Flat and square key
  4. Sunk and saddle key

Saddle keys

A saddle is a key which fits in the keyway of the hub only.

Saddle keys

Advantage of saddle key

  • Since keyway is to be made only in the hub hence its cost is low.

Disadvantage of saddle key

  • Power transmission capacity is low

Sunk key

A sunk key is a key in which half the thickness of key fits into the keyway of hub and remaining half remains in the keyway of shaft.

Sunk key

Advantage of sunk key

  • Power transmission capacity is high compared to saddle key.

Disadvantage of sunk key

  • Since keyway is to be made in both shaft and hub hence its cost is high.

Feather key

A feather key is a parallel key which allows relative axial movement between shaft and hub. These can be used with gears or clutches.

feather key design

Woodruff key

Woodruff key is a sunk key in the form of almost semi circular disc of uniform thickness.

Woodruff key design

Advantage of woodruff key

  • It can tilt and align itself according to the shaft
  • Extra depth of key in the shaft prevents slip of shaft and hub

Disadvantage of woodruff key

  • Due to extra depth of keyway, shaft has low strength
  • No axial movement is permitted between shaft and hub

Also read:

What are Rivets?

What are threaded joints?

What is Recirculating ball screw?

What is power screw?

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