Sunk Key: Types, Advantages, Disadvantages, Uses

In this article, You will learn what is sunk key? Its types, advantages, disadvantages, uses, etc.

Before knowing what is sunk key first of all we have to know what is shaft key and what is keyway so that we can better understand all aspects related to the sunk key.

Shaft Keys are mainly of two types first one is sunk key and the second one is saddle key.

Here we only discuss all about sunk keys so without wasting any time let's get started.

What is Shaft Key?

When a pulley, gear, etc. is to be rotated through the shaft of a machine, A shaft key is used to connect the pulley and gear to the shaft.

When gear and pulley are connected by shaft key, both the parts become one, so when one part rotates, the other also rotates together.  

The shaft key is mainly made of steel.

The shaft key is always fitted parallel to the axis of the shaft.

A shaft key is a type of temporary fastener.

What is Keyway?

The groove in which the shaft key fits is called keyway.

Half of the keyway is fitted in the shaft and half in the pulley or gear so that the grip of the key remains on both the shaft and the pulley. 

What is Sunk Key?

A sunk key is a key in which half of the key fits into the keyway of the pulley and the remaining half resides in the keyway of the shaft.

Types of Sunk Key

There are mainly seven types of sunk keys are used:
  • Gib Head Key
  • Feather Key
  • Woodruff Key
  • Parallel Sunk Key
  • Rectangular or Flat Key
  • Square Key
  • Round or Circular Key

See in the figure different types of sunk keys which are described below in detail.

sunk key
Types of Sunk Key

Gib Head Key

It has a head at one end, which is called Gib Head.  

The key can be easily removed and applied by holding this head.  

This type of sunk key, the head is used to reduce the impact of the hammer thus preventing damage to the shaft

The gib head key tapers in 1: 100 in thickness.

These keys are mostly used to hold the gears and pulleys tightly on the shaft.

Feather Key

It is rectangular.

It is not a taper but is equal in length and width.

It allows relative axial movement between the shaft and hub and keeps the parallel parts of the axis free.

These types of keys are mostly used with gears or clutches.

Woodruff Key

The upper part of the woodruff key is flat and the lower part is semicircular.

The Woodruff key can tilt and align itself according to the shaft.  

In order for the Woodruff key to fit into the shaft, the keyway has to be extra deep, which prevents the shaft and hub from slipping.

Woodruff keys are mostly used to improve the concentricity of the shaft during high-speed rotation.

Parallel Sunk Key

Parallel sunk keys can be either rectangular or square sections but without taper.  

These keys are cheap and easily available.

Parallel keys are mostly used in the manufacturing and automotive industry due to their availability and ease of installation.

Rectangular or Flat Key

Rectangular keys are wider than their height and are sometimes also called a flat key.

They are typically specified for shafts with a diameter of 20 inches.

Square Key

Square keys as their name indicates, are square cross-sectional keys and it can be used for larger shafts.

In square sunk, key width and thickness are equal in dimension.

They are typically specified for shafts with a diameter of 0.25 to 1.0 inches but larger square keys are also available for shafts up to 6.5-inches in diameter.

Round or Circular Key

These keys have circular sections and are drilled partly into the hub holes and partly into the shaft.  

The major advantage of using round keys is that their key drill is re-drilled after assembling the mating part.  

They are generally best suited for low-power drives.

The round key is a taper in 1:50.

Advantages of Sunk Key

  1. The power transmission capacity of the sunk key is high as compared to other keys.
  2. The sunk key has a positive drive so no slip occurs.

Disadvantages of Sunk Key 

  1. Since the keyway is built into both the shaft and the hub, so it costs more.

Uses of Sunk Key

  1. Sunk keys are used in general industrial machinery.
  2. It is more suitable for machine tool applications.

So, I hope I have covered everything about "sunk key."  If you still have any doubts or queries regarding this topic, you can direct mail me or ask through the comments, I will definitely reply to you.  

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Thank You.

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