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Keys, Shafts and Couplings

1. Keys are metal pieces inserted between a shaft and hub to connect them and prevent relative motion. There are several types of keys including sunk, saddle, tangent, round, and splined keys. 2. Sunk keys are half in the shaft keyway and half in the hub keyway. Common types are rectangular, square, parallel, gib head, feather, and woodruff keys. Woodruff keys have a semicircular shape that leaves a protruding flat end for easy adjustment. 3. The length of keys must be designed to transmit the full torsional strength of the shaft based on the key material's shearing strength. An example is given to design the length of a rectangular

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254 views26 pages

Keys, Shafts and Couplings

1. Keys are metal pieces inserted between a shaft and hub to connect them and prevent relative motion. There are several types of keys including sunk, saddle, tangent, round, and splined keys. 2. Sunk keys are half in the shaft keyway and half in the hub keyway. Common types are rectangular, square, parallel, gib head, feather, and woodruff keys. Woodruff keys have a semicircular shape that leaves a protruding flat end for easy adjustment. 3. The length of keys must be designed to transmit the full torsional strength of the shaft based on the key material's shearing strength. An example is given to design the length of a rectangular

Uploaded by

Nauman Khan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPTX, PDF, TXT or read online on Scribd
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MACHINE DESIGN I

Keys and coupling

KEYS
A key is a piece of metal inserted between shaft and hub to
connect these together in order to prevent relative motion
between them.

TYPES OF KEYS
1. Sunk keys
2. Saddle keys
3. Tangent keys
4. Round Keys
5. Splines

1. SUNK KEYS
Half in the keyway of the shaft and half in the key way of hub.
Types
I.
II.
III.
IV.
V.
VI.

Rectangular sunk keys.


Square Sunk Keys
Parallel Sunk keys
Gib head keys.
Feather keys
Wood ruff keys.

I.

RECTANGULAR SUNK KEYS

Figure shows rectangular sunk key


Usual proportion of this key are
Width w= d/4
Thickness t= 2w/3 or d/6
Where d is the diameter of the shaft or diameter of the hole in the
hub.
The key has taper 1 in 100 on top side only.

II. SQUARE SUNK KEYS


The only difference in rectangular and square sunk key is that the
width and thickness of the square keys are the same.
W= t = d/4
Where d is the diameter of the shaft or diameter of the hole in the
hub.

III. PARALLEL SUNK KEYS


Parallel sunk keys may be rectangular or square section uniform in
width and thickness throughout.
Parallel key is taper less.

IV. GIB HEAD KEYS


Rectangular sunk keys with a head at one end is known as gib
head.
Usually provided to facilitate the removal of a key.
Gib head key is shown in figure.

IV. GIB HEAD KEYS


The usual proportion of Gib head key are given.
Width w= d/4
Thickness t= 2w/3 or d/6

V. FEATHER KEY
A key attached to one member of a pair and which permits
relative axial movement is known as feather key.
Special type of parallel key which transmit a turning moment and
also permit axial movement.

PROPORTIONS OF STANDARD PARALLEL,


TAPERED AND GIB HEAD KEYS.

VI. WOODRUFF KEY


Easily adjustable key.
Woodruff keys are semicircular, such that, when installed, they
leave a protruding flat end.
The keyway in the shaft is a semi-circular pocket.
This key is largely used in machine tools and also in automobile
industry.

ADVANTAGES AND DISADVANTAGES


OF WOODRUFF KEY.
Advantages

Disadvantages

2. SADDLE KEYS
Saddle keys are suitable for light duty only.
Saddle keys are mainly of two types
I.
II.

Flat saddle keys.


Hollow saddle keys

2. SADDLE KEYS
I.

Flat saddle keys.


It is a taper key which fits in a keyway in the hub and is flat on the shaft.

II.

Hollow saddle keys

It is a taper key which fits in a keyway in the hub and the bottom of the key is
shaped to fit the curved surface of the shaft.

3. TANGENT KEYS
The tangent keys are fitted in pair at right angles
Each key is to withstand torsion in one direction only.
These are used in large heavy duty shafts

4. ROUND KEYS
Circular in section and fits into holes drilled partly in the shaft and
partly in the hub

5. SPLINES
Sometimes, keys are made integral with the shaft which fits in the
keyways broached in the hub.
Such shafts are known as splined shafts as shown in Fig
These shafts usually have four, six, ten or sixteen splines.
The splined shafts are relatively stronger than shafts having a
single keyway.

FORCES ACTING ON SUNK KEYS

FORCES ACTING ON SUNK KEYS

STRENGTH OF THE KEY

STRENGTH OF THE KEY

STRENGTH OF THE KEY

STRENGTH OF THE KEY

STRENGTH OF THE KEY


In order to find the length of the key to transmit full power of the
shaft, the shearing strength of the key is equal to the torsional
shear strength of the shaft.
We know that the shearing strength of key,

EXAMPLE
Design the rectangular key for a shaft of 50 mm diameter. The
shearing and crushing stresses for the key material are 42 MPa
and 70 MPa.

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