Page 168 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

Tolerance on keys and key ways
Key width (b) h9 for square key, h11 for rectangular key
Key way (b) D10
Thickness (h) h9 for square section, h11 for rectangular section.
Key has chamfer S x 45 where S varies from 0.16 to 3.00mm and key way has radius varying from 0.08 to 2.5mm
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according to the size of the shaft. Depth of key slot 0.6h (approximately on shaft) 0.4h (approximately on hole)
Material for keys: Steel of tensile strength of 600 MPa (60MN/m : 60 kgf/mm approx.)
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Designation of keys: Keys are designated by their Type, width, height and length followed by IS numbers.
Parallel key type A width 70 mm height 36 mm, length 250 mm is designated as parallel key A 70x36x250 IS:2048.

Fixing of key (Fig 5): As the feather keys are parallel, they are likely to get loosened from their position. Except
Type A and B, other keys are fastened to the shaft by means of retaining screws and spring dowel sleeves. The
retaining screws are either slotted cheese head screw (IS:1366) or hexagon socket head cap screws (IS:2269).
Spring dowel sleeves are as per IS:5938. Fig 5 shows how the retaining screws and spring dowels are used.
Width of keys vary from 2 mm to 100 mm and height or thickness varies from 2 mm to 50 mm according to shaft
diameter from 6 mm to 500 mm.
Taper keys: they are rectangular in cross section. They have a taper of 1:100 on the thickness. Taper on the key
helps to hold the hub and shaft together firmly.
The key seat on the shaft is parallel to the axis i.e. uniform depth whereas key way in the hub is tapered to 1:100
to suit the key.
There are three types of taper keys:
Type A - Keys with both ends round.
Type B - Keys with both ends square.
Type C - keys with one end round and other end square.

Fig.6 shows the above keys.
All the edges are chamfered at S x 45 where S varies from 0.16 mm to 1.20 mm according to the width of the
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key (b).
Keys for shafts upto 22 mm dia. are of square section, keys for shafts above 22 mm dia are of rectangular section.
Approximate proportion of sunk keys of rectangular cross section for a shaft of diameter ‘d’.
Width of the key (b) = 0.25d + 2 mm (¼ d + 2 mm)
Thickness of the key (h) = 0.66 b or (2/3b)

Taper 1 in 100 (1:100)
Length = d to 3d (approx.) maximum upto 140 mm.
IS: 2292 lays down the specifications for taper keys and key ways. Width and thickness vary from 2 x 2 to 100 x
50 mm according to the shaft dia ranging from 6mm to 500 mm. Length varies from 6 mm min. to 400 mm max.
A taper key of type B, width 32 mm, height 18 mm, length 100 mm is designated as Taper key B32 x 18 x 100 IS:
2292.
Tolerance on key width ‘b’ is h9 and for thickness h, h9 for square section and h11 for rectangle section. Tolerance
on key way width is D10.
Gib-Head Keys: It is a taper key with a square head chamfered 30 at the thick end of the key. When the key is
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not accessible to remove it, a head is provided called gib. A wedge is placed between the gib and hub, by giving
a jerk to the wedge, the key is removed from assembly.

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CITS :Engineering Drawing (Mechanical) - Exercise 8 CITS :Engineering Drawing (Mechanical) - Exercise 8