Subject: Machine Design -I

Topic: Shaft, Keys and Coupling

Difficulty: Medium

Types of keys:

(a) Sunk keys,

(b) Saddle keys,

(c) Tangent keys,

(d) Round keys, and

(e) Splines.

(a) Sunk keys:

• A sunk key is a key in which half the thickness of the key fits into the keyway on the shaft and the remaining half in the keyway on the hub.
• Therefore, keyways are required both on the shaft as well as the hub of the mating element.

There are two types of sunk keys

1. Square sunk key
2. Rectangular sunk key

Use:

• Square keys are used in general industrial machinery.
• Rectangular keys/ Flat keys are more suitable for machine tool applications

(b) Saddle key:

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

• In this case, there is no keyway on the shaft.

• It is likely to slip round the shaft under load. Therefore it is used for comparatively light loads.

There are two types of saddle keys

1. Hollow saddle key
2. Flat saddle key.

Resistance to slip in case of flat key is slightly more than that of hollow key

Use:

• Saddle keys are suitable for light duty or low power transmission