DESIGN OF KEYS

1. Design of Keys and
Splines

2. Design of Keys
• A key is a piece of mild steel inserted between
the shaft and hub or boss of the pulley to
connect these together.
• Keys prevent relative motion between them.
• A keyway is a slot or recess in a shaft and hub
of the pulley to accommodate a key.

3. Types of Keys
1. Sunk keys
2. Saddle keys
3. Tangent keys
4. Round keys
5. Splines

4. Sunk Keys
• Rectangular: They are provided half in the
keyway of the shaft and half in the keyway of
the hub or boss of the pulley.

5. Sunk Keys
• Square sunk keys:
The only difference between a rectangular sunk
key and a square sunk key is that its width and
thickness are equal. W=t=d/4
• Parallel sunk keys:
Parallel key is a taperless and is used where the
pulley, gear or other mating piece is required to
slide along the shaft

6. Sunk Keys
• Gib head keys:
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.

7. Sunk Key
• Feather Key: A key attached to one member
of a pair and which permits relative axial
movement is known as feather key.It is a
special type of parallel key which transmits a
turning moment and also permits axial
movement. It is fastened either to the shaft or
hub.
•

8. Wooddruff key
• The woodruff key is an easily adjustable key. It
is a piece from a cylindrical disc having
segmental cross-section.
• This key is largely used in machine tool and
automobile construction

9. Advantages of wooddruff key
• It accommodates itself to any taper in the hub
or boss of the mating surface.
• It is useful in tapering shaft ends.
• Disadvantages
1. Depth of the keyway weakness the shaft.
2.It can not be used as a feather

10. Saddle keys
• Flat saddle keys:
• It is a taper key which fits in a keyway in a hub
and is flat on the shaft
• It is used for comparatively light loads.

11. Saddle Key
• 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
• It is usually used as a temporary fastening in
fixing and setting eccentrics, cams etc.

12. Tangent Key
• 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.

13. Splines
• Keys are made integral with the shaft.
• Such shafts are called as splined shafts
• Splined shafts are relatively stronger than
single keyway shafts.
• By using splined shafts,
we obtain axial movement,
positive drive is obtained.

14. Tutorials
• Design a rectangular key for a shaft of 50 mm
diameter. The shearing and crushing stress for
the key materials are 42 Mpa and 70 Mpa.

15. Design of Crankshafts
• A crankshaft (i.e. a shaft with a crank) is used
to convert reciprocating motion of the piston
into rotatory motion or vice versa.
• The crankshaft, dependingupon the position of
crank, may be divided into the following two
types :
• Side crankshaft or overhung crankshaft,
• Centre crankshaft

16. Side Crankshaft and Center
crankshaft

17. Single throw vs Multiple throw
• A crankhaft with only one side crank or centre
crank is called a single throw crankshaft
whereas the crankshaft with two side cranks,
one on each end or with two or more centre
cranks is known as multi-throw crankshaft.

18. Bearing Pressure in Crankshaft
• The following two types of stresses are
induced in the crankshaft.
• Bending stress
• Shear stress due to torsional moment on the
shaft

19. Allowable bending and shear stress

20. Design procedure for crankshaft
• Find the magnitude of the various loads on the
crankshaft.
• Determine the distances between the supports
and their position with respect to the loads.
• The shaft is considered to be supported at the
centres of the bearings and all the forces and
reactions to be acting at these points.

21. Design procedure for crankshaft
• The thickness of the webs is assumed to be
from 0.4 ds to 0.6 ds, where ds is the diameter of
the shaft. It may also be taken as 0.22D to 0.32
D, where D is the bore of cylinder in mm.
• Calculate the distances between the supports
• Assuming the allowable bending and shear
stresses, determine the main dimensions of the
crankshaft.

23. When the crank is at dead centre
• The crankpin as well as ends of the crankshaft
will be only subjected to bending moment.
• Thus, when the crank is at the dead centre, the
bending moment on the shaft is maximum and
the twisting moment is zero.
• (a) Design of crankpin

25. • B) Design of left hand crank web

26. • (c) Design of right hand crank web
• The dimensions of the right hand crank web
(i.e. thickness and width) are made equal to
left hand crank web from the balancing point
of view.

27. d) Design of shafts

28. Materials for Crankshafts
• In industrial engines, the crankshafts are
commonly made from carbon steel such as 40
C 8, 55 C 8 and 60 C 4.
• In transport engines, manganese steel such as
20 Mn 2, 27 Mn 2 and 37 Mn 2 are generally
used for the making of crankshaft.
• In aero engines, nickel chromium steel such as
• 35 Ni 1 Cr 60 and 40 Ni 2 Cr 1 Mo 28 are
extensively used for the crankshaft

29. • The crankshafts are made by drop forging or
casting process but the former method is more
common.
• The surface of the crankpin is hardened by
case carburizing, nitriding or induction
hardening.