Cam Drawing

7/27/2019 Cam Drawing

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ME 114 Engineering Drawing II

Dr. Ouzhan Ylmaz

Assoc.Prof.

Mechanical Engineering

University of Gaziantep

CAM DRAWING


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1

Introduction

A cam is a mechanical device with a surface or groove

that controls the motion of a second part called a follower

in order to convert rotary motion to linear motion (Fig. 1).

Figure 2

Figure 1

The follower, held against the cam by a spring or by gravity,

can be knife, roller, mushroom or flat-faced type (Fig. 2).

Type of follower, timing and manner of movement to be

created by the cam are the main elements in designing cams.


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2

Cam Types

Radial cam: The follower is raised and lowered as the cam revolves (Fig. 3).

Face cam: The follower at the end of an arm oscillates as the

cam revolves (Fig. 4).

Toe (Follower) and Wiper: The cam itself oscillates (Fig. 5).

Figure 3

Positive-Motion Cam (Yoke): The enclosed follower makes

possible the application of force in both directions (Fig. 6).

Cylindrical Groove and End Cams: The follower

moves parallel to the cam axis (Fig. 7). Force is

applied to follower in both directions in groove cam

(left) and in only one direction in end cam (right).

Figure 4 Figure 5 Figure 6

Figure 7


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3

Types of Cam Motion

Cams are designed to move the follower with a

constant velocity, constant acceleration /

deceleration orharmonic motion(from top to

bottom in Fig. 8). In most cases, the combined

motion of follower with rise orfall, or stationary

(dwell) make up the complete cam surface.

In studying the follower motion, a diagram

showing the height of the follower for successivecam positions is frequently employed. These

diagrams are usually made to actual size.

The cam position is shown on the abscissa where

one complete rotation (i.e. 360) of the cam is

divided into equally-spaced intervals, which

are generally 30 although the intermediate

points can also be used. The follower positions

are shown on the ordinate divided into the same

number of intervals as the abscissa.

0 30 60 90 120 150 180 210 240 270 300 360330

1

2

3

4

5

6

1'

2'

3'

4'

5'

6'

1''

2''

3''

4''

5''

6''

Rise (180) Fall (180)

R

R

R

One Complete Revolution (Cycle) of Cam = 360

TotalDisplac

ement

0 30 60 90 120 150 180 210 240 270 300 360330

Rise (180) Fall (180)


1'

2'

3''

2''

1''

1

4

9

4

10

0

3'''

2'''

1'''

01

4

9

0

1

4

9

0

0

3'

1''''

2''''

3''''

0 30 60 90 120 150 180 210 240 270 300 360330

1

2

3

4

5 6

1'

2'

3'

4'

5'

6'

1''

2''

3''

4''

5''

6''

Rise (180) Fall (180)


Figure 8


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4

0 30 60 90 120 150 180 210 240 270 300 360330

1

2

3

4

5

6

1'

2'

3'

4'

5'

6'

1''

2''

3''

4''

5''

6''

Rise (180) Fall (180)

R

R

R


TotalD

isplacement

Constant Velocity

Constant velocity gives a uniform rise and fall as plotted in Fig. 9.

The diagram is constructed by plotting the cam positions on the abscissa, measuring

the total follower movement on the ordinate and dividing it into the same number ofpoints as the abscissa.

As the cam moves one unit of its rotation, the follower likewise moves one unit which

produces the straight line of motion.

Figure 9

The starting and end sections

of the profile are rounded by

fillets of radius which equals

to of total displacement.

This is done due to the

reason that the cam surface

should have smooth transition

during the movement. This

type of motion is called

modified constant velocity.

constant velocitymodified constant velocity


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5

0 30 60 90 120 150 180 210 240 270 300 360330

Rise (180) Fall (180)


1'

2'

3''

2''

1''

1

4

9

4

10

0

3'''

2'''

1'''

01

4

9

0

1

4

9

0

0

3'

1''''

2''''

3''''

Constant Acceleration / Deceleration

With constant acceleration or deceleration, the distance travelled is proportional

to the square of the time (i.e. 1, 4, 9, 16, 25, etc.) where the increments of follower

distance are made proportional to 1, 3, 5, 7, etc. as shown in Fig. 10.Using a scale, the rise of follower is divided into the same number of intervals as

the abscissa, making the first part movement as one unit movement, the second

part as three units, and so on.

The points at the intersection of the coordinate lines are then plotted to obtain the

curve which accelerates and then decelerates when rising and falling.

Figure 10

uniform accceleration

uniform deceleration


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Harmonic Motion

Harmonic motion (sine curve) can be plotted as in Fig. 11 by measuring the rise,

drawing a semicircle, dividing it into the same number of intervals as the abscissa,

and projecting the points on the semicircle as ordinate lines.

Points are plotted at the intersection of the coordinate lines.

The swinging action of a mass at the end of a pendulum is a good example of

harmonic motion.

Figure 11

0 30 60 90 120 150 180 210 240 270 300 360330

1

2

3

4

56

1'

2'

3'

4'

5'

6'

1''

2''

3''

4''

5''

6''

Rise (180) Fall (180)



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Drawing a Cam Profile with Combined Motions

Lets draw a complete drawing of a cam having the following specifications

(The cam is rotating in CCW direction and a roller follower is used)

Base Circle Dia. = 40 mm

Hub Dia. = 20 mm

Shaft Dia. = 10 mm

Plate Thickness = 12 mm

Hub Thickness = 20 mm

Key Way = 2 x 2 mm

Follower Dia. = 6 mm

0 - 60Rise of 12 mm with uniform velocity

60 - 90Dwell

90 - 180Rise of 24 mm with harmonic motion

180 - 210Dwell

at 210Sudden fall of 12 mm

210 - 240Dwell

240 - 360Fall of 24 mm with uniform acceleration


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The Displacement Diagram

The displacement diagram for given cam specifications is shown below.

The circumference is divided into intervals of 30, and the profile of each motion between

specified intervals are plotted. Note that the intervals for harmonic motion are defined as 15.

Then, the intersection points between abscissa and ordinate (shown as A, B, C, etc.) are

connected in order to obtain the complete cam profile.

Figure 12

0 60 90 180 210 360

1

2

3

4

5 6

1'

2'

1

2 2''

3''

4''

5''6''

1''

1

4

9

2'''

3'''

1'''

Circumference = PI * (Base Circle Dia.)

12

24

12

24

dwell harmonic motion dwell uniform accelerationdwelluniform velocity

Base Circle

Cam Profile

240

A

B

C

D

E

F

G

H

J K L

M NP

Q

R

S

0

164'''


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The Cam Drawing

The complete cam drawing is obtained based on the displacement diagram. The ordinate of

each point on displacement diagram is measured and added onto the base circle with a radius

of follower (see the distance of M + follower radius).

Then, the follower circle is plotted having a center point as the end of each ordinate. Note that

the order of placing the points A, B, C, etc. is in CW direction (i.e. the reverse of cam rotation).

After that, the center of

each follower circle is

connected by smoothed

curve to obtain follower

path. This curve is shifted

(i.e. offsetted) towards

the base circle by the

value of radius of follower

in order to obtain the

complete cam surface.

The sectional side view is

also required to show the

plate and hub thickness.

Figure 13

Cam Surface

Follower Path

Base Circle

Hub

Shaft

Key Way

A

B

C

D E FG

H

J

K

LM

N

P

Q

R

S

CamRotatio

n

(CCW)

plate thickness

hub thickness

M+followerradius


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A Case Study Sheet

Base Circle Dia. = 40 mm

Hub Dia. = 20 mm

Shaft Dia. = 10 mm

Plate Thickness = 12 mm

Hub Thickness = 20 mm

Key Way = 2 x 2 mm

Follower Type = Roller

Follower Dia. = 6 mm

Cam Rotation = CCW

0 - 60 Rise = 12 mm

(uniform velocity)

60 - 90 Dwell

90 - 180 Rise = 24 mm

(harmonic motion)

180 - 210 Dwell

at 210 Sudden fall = 12 mm

210 - 240 Dwell

240 - 360 Fall = 24 mm

(uniform acceleration)

0 60 90 180 210 360

1

2

3

4

56

1'

2'1

2 2''

3''

4''

5''6''

1''

1

4

9

2'''

3'''

1'''

Circumference = PI * (Base Circle Dia.)

12

24

12

24

dwell harmonic motion dwell uniform accelerationdwelluniform velocity

Base Circle

Cam Profile

240

A

B

C D

E

F

G

H

JK L

M NP

Q

R

S

0

164'''

Cam Surface

Follower Path

Base Circle

Hub

Shaft

Key Way

A

B

C

D E FG

H

J

K

LM

N

P

Q

R

S

CamRotatio

n

(CCW)

plate thickness

hub thickness

M+followerradius


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Timing Diagrams

When two or more cams are used on the same machine and their functions are

dependent on each other (as in Fig. 14), the 'timing" and relative motions of each

cam can be studied by means of a diagram showing each follower curve.

The curves can be superimposed, but it is better to place them as in Fig. 15.

Figure 15Figure 14

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Cam Drawing