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8/8/2019 Levers Presentation
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Design of Levers
By:
Er. Shankar Sehgal
Faculty of Mech. Engg., UIET,Panjab University, Chandigarh
Website: http://shankarsehgal.weebly.com
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Basics
A lever is a rigid rod or bar capable of turningabout a fixed point calledfulcrum.
The ratio of load lifted to the effort applied is
called mechanical advantage. W l1 = P l2
The ratio of the effort arm to the load arm i.e.l2/ l1 is calledleverage.
1
2
l
l
P
W
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First Type of Lever
Fulcrum is in between load and effort
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Second Type of Lever
Load is in between fulcrum and effort
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Third Type of Lever
Effort is in between load and fulcrum
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Design of a Lever
Known parameters: Load or Weight, W
Parameters to be calculated:
Effort , P or Lever Arm Length, L (Assume P and Calculate Lor vice versa)
Reaction at fulcrum, RF Maximum bending moment acting on cross-section of
lever arm, M
Parameters to be designed: Cross-section of lever arm
Diameter and length of pins
Diameter and length of boss
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Cross-section of Lever Arm
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Hand Lever
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Design of Hand Lever
d = diameter of shaft
d2 = diameter of boss = 1.6 d
t2 = thickness of boss = 0.3 d l2 = length of boss = 1.25 d
t = thickness of lever = 2 t2
B = width of lever = 5 t M = applied bending moment = P x L
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22
2
2
tl
td
LP
A
F
Tearing Failure of Boss:
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Bending Failure of Boss:
12
2
2
2 33222
dtdl
LP
td
I
M
y
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Also design the diameter of shaft at the centre of
bearing by considering the equivalent stresses
concept
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Check for Bending Failure of Lever Arm:
122
3tB
LP
B
I
M
y
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Foot Lever
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Design of Foot Lever
Effort applied = 80 kg = 800 N
Design is similar to a Hand Lever
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Bell Crank Lever
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Design of Fulcrum
Double Shearing Failure of Pin:
42
2
1d
R
A
FF
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Design of Fulcrum
Bearing Failure
of Pin:
11ld
R
A
F F
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Design of Fulcrum
Length of bush = length of fulcrum pin
Thickness of bush = 3 mm
Diameter of bush = 2 x Diameter of pin
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Design of Fulcrum
Check for Bending Failure of Fulcrum:
12
427245
2
72 33
M
I
M
y
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Design of Fork End (if any)
D1 = 2 x d1t1 = l1 / 2
Inner dia. of
each eye =
d1 + 2 x 3 mm
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Design of Fork End (if any)
Bending failure of the
pin at fork end:
64
42322
2
4
1
111
1 d
lWtlW
d
IM
y
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Design of Lever Arm
Use bending failure criteria
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Thank You