Practical 1
Aim: To study the different types of Keys
Definition of a Key:
•A key is a piece of mild steel inserted between the shaft and
hub or boss of the pulley to connect these together in order to
prevent relative motion between them.
•It is always inserted parallel to the axis of the shaft.
•Keys are used as temporary fastenings and are subjected to
considerable crushing and shearing stresses.
•A keyway is a slot or recess in a shaft and hub of the pulley to
accommodate a key.
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Types of Keys
The following types of keys are important from the subject
point of view :
1.Sunk keys
2. Saddle keys
3. Tangent keys
4. Round keys
5. Splines.
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Types of Keys
Sunk Keys
The sunk keys are provided half in the keyway of the shaft and half in the
keyway of the hub or boss of the pulley.
The sunk keys are of the following types :
1. Rectangular sunk key. Usual proportions of this key are :
Width of key, w = d / 4 ; and thickness of key, t = 2w / 3 = d / 6
where d = Diameter of the shaft or diameter of the hole in the hub
The key has taper 1 in 100 on the top side only.
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Types of Keys
Rectangular sunk key
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Types of Keys
2. Square sunk key
The only difference between a rectangular sunk key and a square sunk
key is that its width and thickness are equal, i.e.
w=t=d/4
3. Parallel sunk key
keys may be of rectangular or square section uniform in width and
thickness throughout. It may be noted that a parallel key is a taperless
and is used where the pulley, gear or other mating piece is required to
slide along the shaft.
4. Gib-head key.
It is a rectangular sunk key with a head at one end known as gib head.
It is usually provided to facilitate the removal of key.
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Types of Keys
The usual proportions of the gib head key are :
Width, w = d / 4 ;
and thickness at large end,
t = 2w / 3 = d / 6
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Types of Keys
5. Feather Key
A rectangular key connecting the keyways of a shaft and a hub
of a gear, pulley, etc., fastened in one keyway and free to slide in
the other so that the hub can drive or be driven by the shaft at
various positions along it.
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Feather Key
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Types of Keys
Δ Feather key: A key attached to one member of a pair
and which permits relative axial movement is known as
feather key.
Δ It is a special type of parallel key which transmits a
turning moment and also permits axial movement.
ΔIt is fastened either to the shaft or hub, the key being a
sliding fit in the key way of the moving piece.
ΔThe various proportions of a feather key are same as that
of rectangular sunk key and gib head key.
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Types of Keys
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Types of Keys
Woodruff key.
The woodruff key is an easily adjustable key.
It is a piece from a cylindrical disc having segmental cross-
section in front view as shown in Fig.
.
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Types of Keys
A woodruff key is capable of tilting in a recess milled out in the
shaft by a cutter having the same curvature as the disc from
which the key is made.
This key is largely used in machine tool and automobile
construction.
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Types of Keys
The main advantages of a woodruff key are as follows :
1. It accommodates itself to any taper in the hub or boss of
the mating piece.
2. It is useful on tapering shaft ends. Its extra depth in the
shaft prevents any tendency to turn over in its keyway.
The disadvantages are :
1. The depth of the keyway weakens the shaft.
2. It can not be used as a feather.
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Types of Keys
Saddle keys
The saddle keys are of the following two types :
1.Flat saddle key, and 2. Hollow saddle key
A flat saddle key is a taper key which fits in a keyway in the
hub and is flat on the shaft as shown in Fig.
It is likely to slip round the shaft under load.
Therefore it is used for comparatively light loads.
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Types of Keys
Tangent keys
Saddle keys
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Types of Keys
A hollow saddle key 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.
Since hollow saddle keys hold on by friction,
therefore these are suitable for light loads.
It is usually used as a temporary fastening in fixing
and setting eccentrics, cams etc.
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Types of Keys
Tangent Keys
The tangent keys are fitted in pair at right angles as shown in Fig.
Each key is to withstand torsion in one direction only. These are
used in large heavy duty shafts.
Round Keys
The round keys, are circular in section and fit into holes drilled
partly in the shaft and partly in the hub. They have the advantage
that their keyways may be drilled and reamed after the mating
parts have been assembled. Round keys are usually considered to
be most appropriate for low power drives.
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Types of Keys
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 .
These shafts usually have four, six, ten or sixteen splines.
The splined shafts are relatively stronger than shafts having a single
keyway.
The splined shafts are used when the force to be transmitted is large in
proportion to the size of the shaft as in automobile transmission and
sliding gear transmissions.
By using splined shafts, we obtain axial movement as well as positive
drive is obtained.
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