1. MET 305 MECHANICS OF MACHINES TUTORIAL .5
Student Name & No.________________________________ Date:___________________
Section: _________________________________________ Score: ___________________
Cams
1. Introduction
A cam is a rotating machine element, which gives reciprocating or oscillating motion to another
element known as follower. The cam and the follower have a line contact and constitute a
higher pair. The cams are usually rotated at uniform speed by a shaft, but the follower motion
is predetermined and will be according to the shape of the cam The cam and follower is one of
the simplest as well as one of the most important mechanisms found in machinery today. The
cams are widely used for the inlet and exhaust valves of internal combustion engines,
automatic attachment of machineries, paper cutting machines, spinning and weaving textile
machineries, feed mechanism of automatic lathes etc.
2. Classification of Followers
The followers may be classified as discussed below:
2.1. According to the surface in contact.
The followers, according to the surface in contact, are as follows:
(a) Knife edge follower. When the contacting end of the follower has a sharp knife-edge, it is
knife-edge follower, as shown in Fig. (a). The sliding motion takes place between the surfaces
(i.e. the knife-edge and the cam surface). This is seldom used in practice because the small area
of contacting surface results in excessive wear. In knife-edge followers, a considerable side
thrust exists between the follower and the guide.
(b) Roller follower. When the contacting end of the follower is a roller, it is called a roller
follower, as shown in Fig.(b). Since the rolling motion takes place between the contacting
surfaces (i.e. the roller and the cam), therefore the rate of wear is greatly reduced. In roller followers
also the side thrust exists between the follower and the guide. The roller followers are
extensively used where more space is available such as in stationary gas and oil engines and
aircraft engines.
(c) Flat faced or mushroom follower. When the contacting end of the follower is a perfectly flat
face, it is called a flat-faced follower, as shown in Fig.(c). It may be noted that the side thrust
between the follower and the guide is much reduced in case of flat-faced followers. The only
side thrust is due to friction between the contact surfaces of the follower and the cam. The
relative motion between these surfaces is largely of sliding nature but wear may be reduced by
off-setting the axis of the follower, as shown in Fig.(f) so that when the cam rotates, the
follower also rotates about its own axis. The flat faced followers are generally used where space
is limited such as in cams which operate the valves of automobile engines.
Note : When the flat faced follower is circular, it is then called a mushroom follower.
(d) Spherical faced follower. When the contacting end of the follower is of spherical shape, it is
called a spherical faced follower, as shown in Fig.(d). It may be noted that when a flat-faced
follower is used in automobile engines, high surface stresses are produced. In order to minimize
these stresses, the flat end of the follower is machined to a spherical shape.

2. MET 305 MECHANICS OF MACHINES TUTORIAL .5
2.2.According to the motion of the follower. The followers, according to its motion, are of the
following two types
(a) Reciprocating or translating follower. When the follower reciprocates in guides as the cam
rotates uniformly, it is known as reciprocating or translating follower. The followers as shown in
Fig. 20.1 (a) to (d) are all reciprocating or translating followers.
(b) Oscillating or rotating follower. When the uniform rotary motion of the cam is converted
into predetermined oscillatory motion of the follower, it is called oscillating or rotating
follower. The follower, as shown in Fig 20.1 (e), is an oscillating or rotating follower.
2.3. According to the path of motion of the follower. The followers, according to its path of
motion, are of the following two types:
(a) Radial follower. When the motion of the follower is along an axis passing through the
centre of the cam, it is known as radial follower. The followers, as shown in Fig. (a) to (e) are all
radial followers.
(b) Off-set follower. When the motion of the follower is along an axis away from the axis of the
cam centre, it is called off-set follower. The follower, as shown in Fig. (f), is an off-set follower.
Note : In all cases, the follower must be constrained to follow the cam. This may be done by
springs, gravity
or hydraulic means. In some types of cams, the follower may ride in a groove. important in
order to draw the cam profile.

3. MET 305 MECHANICS OF MACHINES TUTORIAL .5
3. Cam Terminology
3.1. Base circle. It is the smallest circle that can be drawn to the cam profile.
3.2. Trace point. It is a reference point on the follower and is used to generate the pitch
curve. In case of knife edge follower, the knife edge represents the trace point and the
pitch curve corresponds to the cam profile. In a roller follower, the centre of the roller
represents the trace point.
3.3. Pressure angle. It is the angle between the direction of the follower motion and a
normal to the pitch curve. This angle is very important in designing a cam profile. If the
pressure angle is too large, a reciprocating follower will jam in its bearings.
3.4. Pitch point. It is a point on the pitch curve having the maximum pressure angle.
3.5. Pitch circle. It is a circle drawn from the centre of the cam through the pitch points.
3.6. Pitch curve. It is the curve generated by the trace point as the follower moves relative
to he cam. For a knife edge follower, the pitch curve and the cam profile are same whereas
for a roller follower, they are separated by the radius of the roller.
3.7. Prime circle. It is the smallest circle that can be drawn from the centre of the cam and
tangent to the pitch curve. For a knife edge and a flat face follower, the prime circle and
the base circle are identical. For a roller follower, the prime circle is larger than the base
circle by the radius f the roller.
3.8. Lift or stroke(throw, travel). It is the maximum travel of the follower from its lowest
position to the topmost position.

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4. Types of follower motions
1. Uniform velocity
2. Simple harmonic motion

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3. Uniform acceleration and retardation
4. Cycloidal Motion

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5. Objective
a. To understand different types of followers
b. To analyze various types of follower displacements
c. To analyze and draw different types of cams for different types of followers and
motions
6. Procedure
1. Check the type of follower.
2. Study the type of follower motion.
3. Draw the displacement diagram.
4. Construct the cam profile.
7. Problems
1. Draw the profile of a disc cam to give uniform motion (uniform velocity) during outstroke of 25
mm to a knife edge follower during the first half of the cam revolution. The return of the cam also
takes place with uniform motion (uniform velocity) during the remaining half of the cam
revolution. Minimum radius of the cam is 25 mm. Draw the shaft on which the cam is mounted
showing the position of the key. Shaft diameter - 25 mm. The axis of the knife edge follower passes
through the axis of the cam.

7. MET 305 MECHANICS OF MACHINES TUTORIAL .5
2. Draw the cam profile for cam with roller reciprocating follower. The axis of the follower passes
through the axis of the cam and rotates anticlockwise. Particulars of the cam and the follower motion
are the following:
Roller diameter = 5 mm
Minimum radius of the cam = 20 mm
Total lift = 25 mm.
The cam has to lift the follower with simple harmonic motion during 180° of cam rotation, then allow
the follower to drop suddenly halfway, and further return the follower with uniform velocity
during the remaining 180° of cam rotation. Show the position of key on the shaft to which the
cam is mounted. Determine the maximum velocity and maximum acceleration on the outstroke, if
the cam rotates at a uniform speed of 100 r.p.m.
Answer

8. MET 305 MECHANICS OF MACHINES TUTORIAL .5
3.. Cam with 30 mm as minimum diameter is rotating clockwise at a uniform speed of 1200
r.p.m. clockwise and has to give the motion to the roller follower 10 mm diameter as defined
below :
(i ) Follower to complete outward stroke of 25 mm during 120° of cam rotation with
equal uniform acceleration and retardation.
(ii) Follower to dwell for 60° of cam rotation.
(iii) Follower to return to its initial position during 90° of cam, rotation with equal uniform
acceleration and retardation
(iv) Follower to dwell for the remaining 90° of cam rotation.
Layout the cam profile when:
(a) the roller follower axis passes through the axis of the cam ;
(b) the roller follower axis is offset to right by 5 mm.
Determine the uniform acceleration of the follower on the outstroke and the return stroke, and
also the maximum velocity of the follower during outstroke and the return stroke.
Answer

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4. Determine the profile of cam to give oscillatory motion to the follower, with uniform angular
velocity about its pivot. One oscillation is completed in one revolution of the cam. The distance
between the cam centre and the pivot of the follower is 50 mm. The base circle diameter is 40
mm. Angle of oscillation is 29°. The length of the oscillating lever = 50 mm with roller of 5 mm
diameter at the end. The cam rotates anticlockwise.
Answer

10. MET 305 MECHANICS OF MACHINES TUTORIAL .5
5. It is required to set out the profile of a cam to give the following motion to the reciprocating
follower with a flat mushroom contact face:
(i) Follower to have a stroke of 20 mm during 120° of cam rotation;
(ii) Follower to dwell for 30° of cam rotation (ii) follower to return to its initial position during
120° of cam rotation;
(iv) Follower to dwell for remaining 90° of cam rotation. Cam rotates anticlockwise
Answer

11. MET 305 MECHANICS OF MACHINES TUTORIAL .5
6. It is required to set out the profile of a cam to give the following motion to the follower:
(i) Follower to move outwards through 31.4 mm during 180° of cam rotation, with cycloidal
motion;
(ii) Follower to return with cycloidal motion during 180° of cam rotation.
Determine the maximum velocity and acceleration of the follower during the outstroke when the
cam rotates at 2400 r.p.m. clockwise. The base circle of the cam is 30 mm diameter and the roller
diameter of the follower is 10 mm. The axis of the roller is offset by 7.5 mm to the right.

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10. Conclusion
This tutorial enables the student to construct any type of cam profile for any mechanism
design.

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10. Conclusion
This tutorial enables the student to construct any type of cam profile for any mechanism
design.