This document discusses machine elements and power transmission devices used in mechanical engineering. It describes common machine elements like shafts, axles, keys, couplings, bearings, clutches, and brakes. It provides details on their functions, types, materials, and uses. Power transmission devices covered include belt drives, chain drives, and gear drives. Shafts are classified as machine shafts and transmission shafts. Different types of shafts and keys are defined along with their applications in power transmission.

1. Machine elements,
Power Transmission Devices
UNIT NO.I
INTRODUCTION TO MECHANICAL
ENGINEERING
Basic Mechanical Engineering

2. UNIT I
INTRODUCTION TO MECHANICAL ENGINEERING
 Mechanical Elements
Function, Sketch, Description & Uses of –
• Shaft
• Axle
• Keys ( Parallel Keys )
• Coupling ( Rigid Flanged Coupling )
• Bearing ( Ball Bearing )
• Clutch ( Single Plate Clutch )
• Brake ( Disc Brake )
 Power Transmission Devices
Construction, Working, Comparison & Applications of –
• Belt Drive ( Flat & V Belt )
• Chain Drive
• Spur gear drive arranged with simple gear train

3. What is Machine?
Introduction
Machine is a device consisting of various elements arranged
together, so as to perform the prescribe task to satisfy human
needs.
Eg: A pump-set is a machine in which the input is electrical energy,
the pump-set utilizes the electrical energy to perform the
prescribed task of lifting water to the desired location (output).
INPUT
(Source of energy)
MACHINE
(Arrangement of
elements)
OUTPUT
(Prescribed Task)

4. INPUT MACHINE OUTPUT

5. Machine Elements
• Machine element is an individual component or a group of
components of a machine which performs a specific function.
• Its function may be of holding the components together, to
transmit power or to give supports.
• Depending upon these functions only, the machine elements are
following types.
1) Machine elements used for holding the components.
2) Machine elements used for transmitting the power.
3) Machine elements used for support of other components.

6. Machine elements
Machine
elements
Holding
elements
Supporting
elements
Power
transmitting
elements

7. Machine Elements
• Machine elements used for holding the components :-
These type of machine elements include nuts and bolts,
screw, cotters, keys, couplings, pins, revettes.
• Machine elements used for transmitting the power :-
Machine elements like gears, shafts, clutches and
brakes, pulleys, belts, chain, sprocket, are used to transmit
power from one place to another.
• Machine elements used for support of other components:-
Machine elements like bearings, axles, brackets, hangers
etc. are used to give support to rotating or stationary
members.

8. MECHANICAL SYSTEM
MACHINE
SHAFT
BEARING
KEYS
PRIME
MOVER
COUPLING
COUNTER
SHAFT
GEAR
SPINDLE
MACHINE TOOL
WORK PIECE BASE
PULLEY 1
PULLEY 2
BELT
CLUTCH
MAIN
SHAFT

9. Shaft
• Introduction
A shaft is a rotating member/machine element, which is used to transmit
power from one place to another. In order to transfer the power from one
shaft to another the various members such as pulleys, gears, crank etc. are
mounted on it. These members are mounted on the shaft by means of keys or
splines.

11. Types of shafts
1. Transmission 2. Machine shafts
Used to transmit the
power between the
source and the machine
1. Line shaft
2. Counter shaft
It is short rotating shaft
which forms an integral
part of the machine.
1. Spindle
2. crankshaft

12. Axles
• It is non-rotating machine element which
is used to support rotating machine
elements like : wheels, pulleys etc.

13. Sr. No. Shaft Axle
1 Rotating member Non-Rotating member
2 Used to transmit the torque and
support the transmission elements,
like: gears, pulleys
Only used to support the
transmission elements, like:
wheels, pulleys etc
3 It is subject to torque, bending
moment and axial force
It is subjected to bending
moment and axial force
4 Example- line shaft, counter shaft,
spindle, crankshaft
Example:- front axle of car,
wheel axle of motorcycle etc.

14. Types of Shafts
Types :-
1) Axle
An axle is stationary shaft i.e. non
rotating member, which supports
a rotating element like wheel or
hoisting drum and fitted to the
housing by means of bearings.
Axle is subjected to bending load
only and does not transmit any
useful torque.
e.g.
• rear axle of railway wagon
• axle of motor car
• supporting wheels.
A ) Machine shaft:
These shafts form an integral part of the machine itself.
e.g. crank shaft of an I.C. engine.

15. Types :-
2) Spindle:
A spindle is a short rotating shaft.
Spindles are used in all machine
tools to give motion to a cutting
tool or to a work piece.
e.g.
• spindle of drilling machine.
• drive shaft of lathe.

16. Types of Shafts
Types :-
1) Main shaft
It is a primary shaft, which is
driven by the machine shaft and
from which the power is supplied to
the counter shaft.
2) Countershaft
It is a secondary shaft, which
is driven by the main shaft and from
which the power is supplied to the
machine components.
B) Transmission shaft:
These shafts transmit power from the source of power to the machine which
absorbs that power.
e.g. the power is transmitted from motor to compressor by means of a
transmission shaft.
The transmission shaft is usually circular in cross section. The shaft is always
stepped (having different cross sections of shafts) for positioning transmission
elements like gears, pulleys and bearings. Transmission shafts may be solid
or hollow.

17. Types based on structure of Shafts
• Hollow shafts are lighter than
solid shafts. They have more
strength per kg weight of
material compared to solid
shaft.
• The various types of shafts
are as shown in Fig.
• The examples of the hollow
shafts are propeller shafts.
• Main shaft between air
compressor and gas turbine
in air craft engine.

18. SOLID SHAFT
STEPPED SHAFT HOLLOW SHAFT

19. Shaft Material
• The material used for the shaft should have the following properties
1) It should have high strength.
2) It should have good machinability.
3) It should have good heat treatment properties.
4) It should have high wear resistant properties.
5) It should have sufficient hardness.
6) It should be corrosion resistant in marine or corrosive
environments.
7) It should have high modulus of elasticity.
• The material commonly used for shaft is mild steel. The carbon steel
is also used where strength, wear resistance and facility of heat
treatment is needed. The steels are designated as C40, C50, C60 etc.
(that means carbon percentage in the steel is 0.40, 0.50 and 0.60
respectively.) For greater strength alloy steels such as nickel steel,
nickel-chromium steel and molybdenum steel are used.

20. Summary
• Machine element is an individual component or a group of
components of a machine which performs a specific function.
• Machine elements are used for holding the components, for
transmitting the power, for the support of other component.
• A shaft is a rotating member or machine element, which is used to
transmit power from one place to another.
• Shafts are classified as
i) Machine shaft ii) Transmission shaft
Review Questions
1) State the various functions of machine elements, with application.
2) What are the d material properties of shaft ?
3) Give the types of shafts with their application.
4) Differentiate between transmission shaft and axle.

21. Keys
A key is a machine element used on shafts to secure the rotating elements
like gears, pulleys or sprockets and prevent the relative motion between the
two. 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.
Materials used:
 Plain carbon steels
 Alloy steels

22. • A key performs following two basic functions.
1) The primary function of key is to transmit the torque from the
shaft to the hub of machine element and vice-versa.
2) The second function of the key is to prevent relative rotational
motion between the shaft and mounted machine element like gear
or pulley.
• In most of the cases, key also prevents axial motion between the
elements.
• A keyed joint consisting of shaft, hub and key is illustrated in Fig.
• A recess or slot machined on the shaft and or in the hub to
accommodate the key is called as key way.
• One key way is usually cut by milling machine.
• Keys are designed in order to withstand shear and compressive
stresses resulting from transmission of torque.
• Generally, material of the key is selected, which has less strength
than the shaft material.

23. Types of Keys
• Keys are broadly classified as
a) Saddle keys
b) Sunk keys
c) Round key
d) Splines

24. Keys

26. Parallel key
Parallel keys are the most widely used. They
have a square or rectangular cross-section.
Square keys are used for smaller shafts and
rectangular faced keys are used for shaft
diameters over 6.5 in
SS- 410 & SS- 316 material
used in automobile industries, Textile Industries, machine tool industries,
Motor & pump Industries, Cement Industries etc

27. Saddle Keys
• Saddle keys are fitted only in the key way of one
member of the mating surface i.e. either shaft or hub.
• Saddle keys are only of uniform width, and tapered in
thickness along the length.
• Power transmission of the saddle key is due to the
frictional forces set up between the keys and the shaft.
• Saddle keys are of two types -
i) Flat saddle key
ii) Hollow saddle key

28. Flat Saddle Key
• The flat saddle key is a
taper key which fits in a
key way in the hub and
is flat on the shaft as
shown in Fig.

29. Hollow Saddle Key
• A hollow saddle key is a
taper key which fits in a key
way in the hub and its lower
surface of the key is hollow
or curved to fit on the
curved surface of the shaft
as shown in Fig.

30. • Advantages of Saddle Keys
1) Construction is simple.
2) Mounting cost is less as compared to other keys as there is
key way on the hub only.
3) No weakning of shaft as there is no key way.
• Disadvantages of Saddle Keys
1) Used for transmission of lighter loads only.
2) No positive transmission of power as means of power
transmission in friction.
• Applications
Used for light loads only like temporary fastening in fixing
and setting of eccentric cams etc.

31. Sunk Keys
• Sunk keys are inserted half in the key way of hub and half in
the key way of the shaft. Sunk keys are of uniform width and
tapered in thickness along the length.
• Power transmission of the sunk key is due to the tangential
force between key and mating surfaces. Due to the key
inserted between key ways in both hub and the shaft there is
no relative motion between the shaft and hub. Thus there is
no slip between them. Hence it is a positive drive.
• Sunk keys are of following types.
i) Parallel sunk key
ii) Taper sunk key
iii) Feather key
iv) Woodruff key

32. Parallel SunkKey
A parallel key is square
or rectangular in cross
section and of uniform
thickness and width
over its length.
Parallel sunk keys with
rectangular and square
cross section is shown in
Figs.

33. Gib Headed Key
• The gib head keys are
ordinary sunk keys
tapered on top with a
raised head on one side
so that its removal is
easy. This is shown in
figure.

34. Feather Key
Some feather key
arrangements are
shown in figure.
A feather key is used
when one component
slides over another.
The key may be
fastened either to the
hub or the shaft and
the keyway usually
has a sliding fit.

35. Woodruff Key
A woodruff key is a form of sunk key
where the key shape is that of a
truncated disc, as shown in figure.
It is usually used for shafts less than
about 60 mm diameter and the
keyway is cut in the shaft using a
milling cutter.
It is widely used in machine tools and
automobiles due to the extra
advantage derived from the extra
depth.

37. Coupling
It is the mechanical element used to connect two shaft of a
transmission system and transmit the torque from one shaft to
another
Coupling

38. Types of Coupling
• Rigid couplings
– Muff and sleeve coupling
– Split muff or compression coupling
– Flanged coupling
• Flexible Couplings
– Bushed-pin type flexible coupling
– Oldham coupling
– Universal coupling

39. Rigid Flanged coupling

41. Rigid couplings
• Rigid couplings do not allow any misalignment
of connecting members.
• Not of absorbing shocks and vibration.
Muff and sleeve coupling
Use to connect two line shafts
•Muff and sleeve coupling
•Split muff or compression coupling
•Flanged coupling

42. Split muff or compression coupling

43. Flexible couplings
• It is used to connect shafts having small
amount of lateral or/and angular
misalignment.
• These coupling are capable of absorbing
shocks and vibration.
•Bushed-pin type flexible coupling
•Oldham coupling
•Universal coupling

44. Bushed-pin type flexible coupling
Used to connect diesel engine to generator

45. Oldham coupling
Use to connect Two eccentric shafts

46. Universal coupling

47. Sr.
No.
Comparison Parameters Rigid Coupling Flexible Coupling
1 Purpose To connect two shafts which
are perfectly aligned
To connect two
shafts having small
misalignment
2 Alignment Cannot tolerate any
misalignment
Can tolerate any
misalignment
3 Shock and vibration Cannot absorb Shock and
vibration
Can absorb Shock
and vibration
4 Deflection Deflection is less Deflection is more
5 Cost Less expensive More expensive

48. Bearings
Introduction
• Bearing is a mechanical element, which supports the
rotating element. Thus it permits the relative rotating
motion between two parts.
• Due to relative motion, a moving part comes in contact
causing friction with the stationary part, resulting wear
of mating surface. To reduce the frictional resistance
and wear, a lubricant is provided between the mating
surface.
• A lubricant is a substance placed between the two
surfaces which reduces friction, wear and takes away
heat is known as lubricant.
• Generally mineral oil, vegetable oil or grease are used as
lubricant in bearings.

49. Types of Bearings
a) Sliding Contact Bearings
b) Rolling Contact Bearings

50. Sliding Contact Bearings
• In sliding contact bearings, the motion between the
shaft and the bearing is purely sliding. Because of the
surface contact, the friction between the rotating
shaft and bearing surface is high and hence
lubrication is necessary.
• They are used for crankshaft in I.C. engine, ball mills,
centrifugal machines in sugar industry, turbo-
generators centrifugal pumps. etc.

51. Rolling Contact Bearing
• Rolling motion takes place along the surfaces
of contact between the parts. Steel balls or
rollers are interposed between the moving
and fixed elements, which offer rolling
friction. They are also known as antifriction
bearings. They have point or line contact with
moving element.

52. Ball bearing
Single Row Double Row

53. The Ball Bearing
• It is as shown in Fig.
• It also consists of four major
parts.
(i) Outer race
(ii) Inner race
(iii) Balls and
(iv) Cage
• It consist of number of balls placed between the races. The balls are
placed properly by the cage, which acts like a separator. All balls are
free to rotate within the cage and are able to roll inside the outer
race and inner race.
• A position clearance is kept between the races to accomplish slight
misalignment of balls due to load.
• Ball bearings are able to take only radial loads. It is used in high speed
applications like grinders, cutters etc.
• Deep groove ball bearings are able to sustain radial load as well as
axial (thrust) load.

54. Deep Groove Ball Bearing

55. Cylindrical Roller Bearing

56. Angular Contact Bearing

57. Taper Roller Bearing

58. Self-Aligning Bearing

59. Thrust Ball Bearing

60. Sr. No. Comparison parameter Ball bearing Roller Bearing
1 Rolling bearing Spherical ball Cylindrical roller
2 Nature of contact Point contact Surface contact
3 Load carrying capacity low High
4 Radial dimensions More Less, use for
compactness
5 Axial dimensions less more

61. Sr. No. Comparison parameter Sliding contact bearing Rolling contact bearing
1 Nature of relative motion sliding rolling
2 Starting friction high low
3 Running friction low High
4 Load carrying capacity More Less, use for compactness
5 Nature of load Can take shock load Poor in taking shock load
6 Type of load Either radial or axial Can take combine radial & axial
7 speed Suitable for high speed application Not suitable for high speed
8 Life More Less
9 Positional accuracy Poor Good
10 Lubrication Required continuous supply Not Required continuous supply
11 Noise Noise less More noise
12 Initial cost High Low
13 Maintenance More less
14 Application Steam and gas engine, crankshaft
bearing, marine, conveyors, centrifugal
pumps
Automotive gear box, m/c spindle,
automobile

62. Single plate clutches

63. Multi-plate clutch

67. Brakes
• It is the mechanical device used to slow down or
completely stop the motion of a moving system by
applying an artificial frictional resistance.

68. Caliper disc brake
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69. Power Transmission Devices
• Belt drive,
• chain drive,
• gear drive

70. BELT DRIVES
The belts or ropes are used to transmit
power from one shaft to another by means
of pulleys which rotate at the same speed
or at different speeds.
The amount of power transmitted depends
upon the following factors:
1. The velocity of the belt.
2. The tension under which the belt is placed
on the pulley.
3. The arc of contact between the belt and
the smaller pulley
4. The condition under which the belt is used.
5. The material of the belt used.
Selection of the Belt Drive:
1. Speed of the driving and driven shafts.
2. Speed reduction ratio
3. Power to be transmitted
4. Centre distance between the shafts.
5. Positive drive requirements.
6. Shaft layout.
7. Space available.
8. Service conditions.

71. Types of Belt Drives
Light Drives: used to transmit small powers at belt speeds up to about
10 m/s in agricultural machines and small machine tools.
Medium Drives: Used to transmit medium power at belt speeds over
10 m/s but up to 22 m/s as in machine tools.
Heavy Drives: Used to transmit large powers at belt speed above 22 m/s as in compressor
& generators.

72. Types of Belt [According to Shape]
Flat Belt : used in factories
and workshops, where a
moderate amount of power is
to be transmitted, from one
pulley to another when two
pulleys are not more than 8 m
apart.
V-Belt : used in factories
and workshops, where a
moderate amount of power
is to be transmitted, from
one pulley to another when
two pulleys are very near to
each other.
Circular or Rope Belt :
used in factories and
workshops, where a greater
amount of power is to be
transmitted, from one pulley to
another when two pulleys are
not more than 8 m apart.
e.g. Crane
Timing Belt : They are toothed belts which transmit
power by means of teeth rather than friction. Hence there is
no slip occurring in these types of belts. They need toothed
wheels. e.g. CNC m/c, Automobiles

79. Types of Belt [According to Materials]
Leather Belt : Leather belts are made from
1.2 m to 1.5 m long strip cut from either side of
the back bone of the top grade steer hide.
The leather may be oak- tanned and Chrome
tanned. Leather belts are used in steam & oil
condition.
No. of layers: Single, Double, Triple ply belts.
Rubber belt : These are made from
layers of fabric impregnated with
rubber composition. They can not
withstand in hot, oily and greasy
conditions. They are very flexible and
can be made endless. They are used
in saw mills, paper mills etc.
Cotton or fabric belt : These belts are
made from folding canvas or cotton duck.
They are impregnated with linseed oil to
make water proof. They are suitable in warm
climates, in damp atmosphere. They are
used in form machinery, belt conveyor etc.
i.e. Flooring mills

80. Types of Belt Drive [According to its Arrangement]
The power from one pulley to another can be transmitted by
different arrangement of the belts.
Open Belt Drive :
It is used, when shafts are arranged
parallel and rotating in the same
direction, In this case, the driver A pulls
the belt from one side (i.e. lower side)
and delivers it to the other side (j,e.
upper side).
Thus the tension in the lower side belt
will be more than that in the upper side
belt. Hence lower side belt is known as
tight side, whereas the upper belt is
known as slack side,

81. Cross Belt Drive :
This belt drive is used when shaft
are arranged parallel and rotating
in the opposite direction. A crossed
belt drive can transmit more power
than open belt drive, as the angle
of wrap is more. However, the belt
has to bend in two different planes
and it wears out more.
Types of Belt Drive [According to its Arrangement]

82. Quarter Turn Belt Drive :
The quarter turn drive always
known as right angle belt drive,
is used with shafts arranged at
right angles and rotating in one
definite direction. In order to
prevent the belt from leaving
the pulley, the width of the face
of the pulley should be greater
or equal to 1.4 b, where b- is
the width of the belt. when the
reversible motion is desired,
then a quarter turn belt drive
with guide pulley.
Types of Belt Drive [According to its Arrangement]

83. Belt Drive with idler Pulleys :
A belt drive with an idler pulley, used
with shafts arrangement parallel and
when an open belt drive can not be
used due to small angle of contact on
the smaller pulley. This type of drive is
provided to obtain in high velocity ratio
and when the required belt tension
cannot be obtained by other means.
When it is desired to transmit motion
from one shaft to several shafts, all
arranged in parallel, a belt drive with
many ideal pulleys can be employed.
In conveyer system to avoid slackness
of the belt, idler pulleys are used.
Types of Belt Drive [According to its Arrangement]

84. Compound Belt Drive :
It is used to transmit power from
one shaft to another through a
number of pulleys.
Types of Belt Drive [According to its Arrangement]

85. Stepped or Cone Pulley Drive :
A stepped or cone pulley drive, used
for changing the speed of the driven
shaft while the main or driving shaft
runs at constant speed. This is
accomplished by shifting the belt from
one part of the steps to the another.
Types of Belt Drive [According to its Arrangement]

86. Velocity ratio
It is the ratio between the velocities of the driver and the follower or driven

87. In belt drives, slipping of belt may
occur.
In order avoid slipping, steel
chains are used,
The chains are made up of rigid
links which are hinged together in
order to avoid the necessary
flexibility for warping around the
driving and driven wheels.
The wheels have projecting teeth
and fit into the corresponding
recesses, in the links of The
chain.
The wheels and the chain are
constrained to move together
without slipping and ensures
perfect velocity ratio.
The toothed wheel are known as
sprocket wheels or simply
sprockets.
These wheels resemble to spur
gears
Chain Drive

88. Link Chain
These chains are used for hoisting and hauling purposes.
The links of this type of chain are of oval or square shape.
The joint of each link is welded. The sprockets which are used
for this type of chain have receptacles to receive the links.
Such type of chains are used only at low speeds such as in chain
hoists and in anchors for marine works, cranes and dredges.

89. Block Chain
These chains are used for transmission of power, when the distance
between the centers of shafts is short. These chains have provision for
efficient lubrication.
A block or bush chain is shown in figure. This type of chain was used
in the early stages of development in the power transmission.
It produces noise when approaching or leaving the teeth of the
sprocket because of rubbing between the teeth and the links. Such type
of chains are used to some extent as conveyor chain at small speed.

90. Roller Chain
 A roller chain consists of outer plates or pin link plates, inner
plates or roller link plates, pins, bushes and rollers. A pin
passes through the bush which is secured in the holes of the
roller between the two sides of the chain. The rollers are free
to rotate on the bush which protect the sprocket wheel teeth
against wear. The pins, bushes and rollers are made of alloy
steel.

91. Advantages of Chain Drive over Belt Drive
1. As no slip takes place during chain drive, perfect velocity ratio is obtained.
2. Since the chains are made of metal, therefore they occupy less space in width
than a belt or rope drive.
3. The chain drives can be used when the distance between the shafts is less.
4. It has high power transmitting capacity than belt drive.
5. It gives high transmission efficiency (Upto 98%).
6. The chain drive gives less load on the shafts.
7. A number of shafts can be driven in the same or opposite direction by means of
chain from a single driving sprocket.
8. It permits high speed reduction ratio upto 10 : 1 in one step.
9. It can be operated under adverse temperature and atmospheric conditions.
10. Chain drives are more compact than belt drive.

92. 1. Compared with belt drives, chain drive require precise alignment
of shafts.
2. Compared with belt drives, chain drives require proper
maintenance, particularly lubrication and slack adjustment.
3. The production cost of chain is relatively high.
4. They generate noise.
Dis-advantages of Chain Drive over Belt Drive

93. 1. Bicycles, motor cycles
2. Agriculture machinery
3. Conveyors
4. Rolling mills
5. Road rollers
6. Metal and wood working machinery
7. Textile industry
8. Building construction
9. Material handling equipment
Application Chain Drive

95. Gear drive

96. Types of gears
• Parallel axis
• Intersecting
• Non-intersecting and perpendicular
• Non-intersecting and non-perpendicular

98. Parallel axis

100. Parallel gears also classified

101. Intersecting axes gears

102. Non-intersecting and perpendicular

103. Non-intersecting and non-perpendicular

104. SIMPLE GEAR TRAIN

105. Velocity ratio