PPT: Shafts | Design of Machine Elements - Mechanical Engineering PDF Download

 Page 1


Design of Shaft
• A shaft is a rotating member usually of circular cross-section (solid 
or hollow), which transmits power and rotational motion. 
• Machine elements such as gears, pulleys (sheaves), flywheels, 
clutches, and sprockets are mounted on the shaft and are used to 
transmit power from the driving device (motor or engine) through a 
machine. 
• Press fit, keys, dowel, pins and splines are used to attach these 
machine elements on the shaft. 
• The shaft rotates on rolling contact bearings or bush bearings.  
• Various types of retaining rings, thrust bearings, grooves and steps
in the shaft are used to take up axial loads and locate the rotating 
elements.
• Couplings are used to transmit power from drive shaft (e.g., motor) 
to the driven shaft (e.g. gearbox, wheels).
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Page 2


Design of Shaft
• A shaft is a rotating member usually of circular cross-section (solid 
or hollow), which transmits power and rotational motion. 
• Machine elements such as gears, pulleys (sheaves), flywheels, 
clutches, and sprockets are mounted on the shaft and are used to 
transmit power from the driving device (motor or engine) through a 
machine. 
• Press fit, keys, dowel, pins and splines are used to attach these 
machine elements on the shaft. 
• The shaft rotates on rolling contact bearings or bush bearings.  
• Various types of retaining rings, thrust bearings, grooves and steps
in the shaft are used to take up axial loads and locate the rotating 
elements.
• Couplings are used to transmit power from drive shaft (e.g., motor) 
to the driven shaft (e.g. gearbox, wheels).
Visit for more Learning Resources
The connecting shaft is loaded 
primarily in torsion.
Page 3


Design of Shaft
• A shaft is a rotating member usually of circular cross-section (solid 
or hollow), which transmits power and rotational motion. 
• Machine elements such as gears, pulleys (sheaves), flywheels, 
clutches, and sprockets are mounted on the shaft and are used to 
transmit power from the driving device (motor or engine) through a 
machine. 
• Press fit, keys, dowel, pins and splines are used to attach these 
machine elements on the shaft. 
• The shaft rotates on rolling contact bearings or bush bearings.  
• Various types of retaining rings, thrust bearings, grooves and steps
in the shaft are used to take up axial loads and locate the rotating 
elements.
• Couplings are used to transmit power from drive shaft (e.g., motor) 
to the driven shaft (e.g. gearbox, wheels).
Visit for more Learning Resources
The connecting shaft is loaded 
primarily in torsion.
Combined bending and torsion loads on shaft: 
Shaft carrying gears.
From power and rpm find the torque (T), which gives rise to shear stress.
From Torque (T) and diameter (d), find F
t
= 2T/d. From F
t
and pressure 
angles of gears you can find F
r
and F
a
.
F
r 
and F
t
are orthogonal to each other and are both transverse forces to 
the shaft axis, which will give rise to normal bending stress in the shaft. 
When shaft rotates, bending stress changes from tensile to compressive 
and then compressive to tensile, ie, completely reversing state of stress. 
F
a
will give rise to normal axial stress in the shaft.
Page 4


Design of Shaft
• A shaft is a rotating member usually of circular cross-section (solid 
or hollow), which transmits power and rotational motion. 
• Machine elements such as gears, pulleys (sheaves), flywheels, 
clutches, and sprockets are mounted on the shaft and are used to 
transmit power from the driving device (motor or engine) through a 
machine. 
• Press fit, keys, dowel, pins and splines are used to attach these 
machine elements on the shaft. 
• The shaft rotates on rolling contact bearings or bush bearings.  
• Various types of retaining rings, thrust bearings, grooves and steps
in the shaft are used to take up axial loads and locate the rotating 
elements.
• Couplings are used to transmit power from drive shaft (e.g., motor) 
to the driven shaft (e.g. gearbox, wheels).
Visit for more Learning Resources
The connecting shaft is loaded 
primarily in torsion.
Combined bending and torsion loads on shaft: 
Shaft carrying gears.
From power and rpm find the torque (T), which gives rise to shear stress.
From Torque (T) and diameter (d), find F
t
= 2T/d. From F
t
and pressure 
angles of gears you can find F
r
and F
a
.
F
r 
and F
t
are orthogonal to each other and are both transverse forces to 
the shaft axis, which will give rise to normal bending stress in the shaft. 
When shaft rotates, bending stress changes from tensile to compressive 
and then compressive to tensile, ie, completely reversing state of stress. 
F
a
will give rise to normal axial stress in the shaft.
Loads on shaft due to pulleys
Pulley torque (T) = Difference in belt 
tensions in the tight (t
1
) and slack (t
2
) 
sides of a pulley times the radius (r), ie 
T = (t
1
-t
2
)xr 
Left pulley torque
T
1
= (7200-2700)x380=1,710,000 N-mm
Right pulley has exactly equal and 
opposite torque:
T
2
= (6750-2250)x380=1,710,000 N-mm
F
V2
Bending forces in vertical (F
v
) and horizontal (F
H
) directions: 
At the left pulley: F
V1
=900N; F
H1
=7200+2700 = 9900N
At the right pulley: F
V2
=900+6750+2250=9900N; F
H2
=0
Page 5


Design of Shaft
• A shaft is a rotating member usually of circular cross-section (solid 
or hollow), which transmits power and rotational motion. 
• Machine elements such as gears, pulleys (sheaves), flywheels, 
clutches, and sprockets are mounted on the shaft and are used to 
transmit power from the driving device (motor or engine) through a 
machine. 
• Press fit, keys, dowel, pins and splines are used to attach these 
machine elements on the shaft. 
• The shaft rotates on rolling contact bearings or bush bearings.  
• Various types of retaining rings, thrust bearings, grooves and steps
in the shaft are used to take up axial loads and locate the rotating 
elements.
• Couplings are used to transmit power from drive shaft (e.g., motor) 
to the driven shaft (e.g. gearbox, wheels).
Visit for more Learning Resources
The connecting shaft is loaded 
primarily in torsion.
Combined bending and torsion loads on shaft: 
Shaft carrying gears.
From power and rpm find the torque (T), which gives rise to shear stress.
From Torque (T) and diameter (d), find F
t
= 2T/d. From F
t
and pressure 
angles of gears you can find F
r
and F
a
.
F
r 
and F
t
are orthogonal to each other and are both transverse forces to 
the shaft axis, which will give rise to normal bending stress in the shaft. 
When shaft rotates, bending stress changes from tensile to compressive 
and then compressive to tensile, ie, completely reversing state of stress. 
F
a
will give rise to normal axial stress in the shaft.
Loads on shaft due to pulleys
Pulley torque (T) = Difference in belt 
tensions in the tight (t
1
) and slack (t
2
) 
sides of a pulley times the radius (r), ie 
T = (t
1
-t
2
)xr 
Left pulley torque
T
1
= (7200-2700)x380=1,710,000 N-mm
Right pulley has exactly equal and 
opposite torque:
T
2
= (6750-2250)x380=1,710,000 N-mm
F
V2
Bending forces in vertical (F
v
) and horizontal (F
H
) directions: 
At the left pulley: F
V1
=900N; F
H1
=7200+2700 = 9900N
At the right pulley: F
V2
=900+6750+2250=9900N; F
H2
=0
From Horizontal forces (F
H
) and vertical 
forces (F
v
), Bending moments M
H
& M
V
are 
drawn separately. 
Then the resultant moments at various 
points on the shaft can be found from  
Torque and Bending moment diagrams for the pulley  
system
2 2
V H R
M M M ? ?
F
H
9900N
M
H
2,227,500
F
V
900N 9900N
M 
V
2,227,500
911,250 
T
1 T
2
Torque diag.
1,710,000 N-mm
Resultant bending moment
2,227,500 
2,406,685
2 2
V H R
M M M ? ?
The section of shaft where the left pulley 
is located has obviously the highest 
combination of Torque (1,710,000 N-mm) 
and Bending moment (2,406,685 N-mm)