Levers Presentation

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

Documents

Levers Presentation