Engineeringdrawingi 090303074237-phpapp01

Courses outline
• Introduction; Basic concepts of engineering
drawing; Instruments and their uses; First and
third angle projections; Orthographic drawings;
Principal views, Isometric views; Missing lines
and views; Sectional views and conventional
practices; Auxiliary views.

Lec. Bhuiyan Shameem Mahmood

2

Text & Ref books
• Fundamentals of
Engineering Drawing
-by French & Vierck.
• Metric Drafting
– by Paul Wallah.
• Drafting Technology and
Practice
– by William P. Spence
• Mechanical Engineering
Drawing
-by Dr. Md. Quamrul Islam

3

Class Schedule
1. Introduction: Basic Drawing Practice
2. Orthogonal views of simple block
3. Orthogonal views with circular holes
4. Orthogonal views with fillets and rounds
5. Sectional views
6. Sectional views (conventional practices)
7. Auxiliary views
8. Isometric views
9. Isometric views with circular holes
10.Missing Lines and Missing views.

4

Note:
• If a student fails to attend in any drawing class,
he/she will get ZERO GRAD in that drawing.
• No student will be allowed in the class without
necessary INSTRUMENTS and INSTRUCTION
SHEET.
• There will be a QUIZ EXAM /an ORAL EXAM
during the term time. Marks obtained in these
exams and those in drawing performed in the
classes will be added together to calculate the
final grade.

5

Graphics Language


6

Effectiveness of Graphics Language
1. Try to write a description of
this object.
2. Test your written description
by having someone attempt
to make a sketch from your
description.
You can easily understand that …

The word languages are inadequate for describing the
size, shape and features completely as well as
size
concisely.

7

Composition of Graphic Language
Graphic language in “engineering application” use
lines to represent the surfaces, edges and contours
surfaces
of objects.
The language is known as “drawing” or “drafting” .
drawing
drafting
A drawing can be done using freehand, instruments
freehand
or computer methods.


8

Freehand drawing
The lines are sketched without using instruments other
than pencils and erasers.

Example


9

Instrument drawing
Instruments are used to draw straight lines, circles, and
curves concisely and accurately. Thus, the drawings are
usually made to scale.

Example


10

Computer drawing
The drawings are usually made by commercial software
such as AutoCAD, solid works etc.

Example


11

Introduction
An engineering drawing is a type of technical
drawing, used to fully and clearly define
requirements for engineered items, and is usually
created in accordance with standardized
conventions
for
layout,
nomenclature,
interpretation, appearance size, etc.
Its purpose is to accurately and unambiguously
capture all the geometric features of a product or
a component.
The end goal of an engineering drawing is to
convey all the required information that will allow
a manufacturer to produce that component.

13

Purpose of an Engineering Drawing
1. An engineering drawing is not an illustration.
2. It is a specification of the size and shape of a part or assembly.
3. The important information on a drawing is the dimension and
tolerance of all of its features.


14

Elements of Engineering Drawing
Engineering drawing are made up of graphics language
and word language.
language
Graphics
language
Describe a shape
(mainly).

Word
language
Describe size, location and
specification of the object.

15

Basic Knowledge for Drafting

Word
language

Graphics
language
Line
types

Projection
method

Geometric
construction


Lettering

16

PROJECTION METHOD

Perspective

Parallel
Oblique

Axonometric

Orthographic

Multiview
18

PROJECTION THEORY
The projection theory is used to graphically represent
3-D objects on 2-D media (paper, computer screen).

The projection theory is based on two variables:
1) Line of sight
2) Plane of projection (image plane or picture plane)


19

Line of sight

is an imaginary ray of light between an

observer’s eye and an object.
There are 2 types of LOS : parallel and converge
Parallel projection

Perspective projection

Line of sight
Line of sight


20

Plane of projection is an imaginary flat plane which
the image is created.
The image is produced by connecting the points where
the LOS pierce the projection plane.
Parallel projection

Perspective projection

Plane of projection

Plane of projection


21

Disadvantage of
Perspective Projection
Perspective projection is not
used by engineer for manufacturing of parts, because
1) It is difficult to create.
2) It does not reveal exact
shape and size.

Width is distorted


22

Orthographic projection
• Orthographic" comes from the Greek word for
"straight writing (or drawing)." This projection shows
the object as it looks from the front, right, left, top,
bottom, or back, and are typically positioned relative
to each other according to the rules of either “First
Angle” or “Third Angle” projection.


24

Pictorial
3-dimensional representations
One-point
one vanishing point
lines that are not vertical
or horizontal converge to
single point in distance

Two-point or Three-point
two or three vanishing points

With two points, vertical or
horizontal lines parallel, but not both
With three-point, no lines are parallel

Isometric

Drawing shows corner of object,
but parallel lines on object are
parallel in drawing
Shows three dimensions, but no
vanishing point(s)

25

One-point

Two-Point


26

Symbols for Third Angle (right)or First Angle (left).

First angle projection is the ISO standard and is primarily used in
Europe. The 3D object is projected into 2D "paper" space as if you
were looking at an X-ray of the object: the top view is under the
front view, the right view is at the left of the front view.
Third angle projection is primarily used in the United States and
Canada, where it is the default projection system according to BS
8888:2006, the left view is placed on the left the top view on the
top.

27

MEANING
Orthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane
Object views from top

1

2

1 5

2

3 4

5
3
4
Projection plane

28

Image of a part represented in First Angle Projection


29

Orthographic / Multiview
• Draw object from two / three perpendicular views

/ Orthographic


What it looks
like pictorially

30


31


32

ORTHOGRAPHIC VIEW
Orthographic view depends on relative position of the object
to the line of sight.

Rotate

Two dimensions of an
object is shown.

Tilt

More than one view is needed
to represent the object.

Multiview drawing
Three dimensions of an object is shown.
Axonometric drawing

33

Multiview Drawing
Advantage

It represents accurate shape and size.

Disadvantage Require practice in writing and reading.
Example

Multiviews drawing (2-view drawing)


34

Axonometric (Isometric) Drawing
Advantage

Easy to understand

Disadvantage

Shape and angle distortion

Example

Distortions of shape and size in isometric drawing

Circular hole
becomes ellipse.

Right angle becomes obtuse angle.

35

Isometric projection


36

Isometric projection


37

Sectional views


38

Auxiliary Views
• Used to show true dimensions of an inclined
plane.


39

Auxiliary projection


40

Auxiliary projection


41

Instruments
Drawing board/table.
Drawing sheet/paper.
Drafting tape.
Pencils.
Eraser.
Sharpener.
T-square.
Set-squares/triangles.
Scales.
Compass and divider.

43

Drawing board


44

Drawing table


45

Drawing sheet/paper
•
•
•
•

216 X 280 mm
280 X 382 mm
382 X 560 mm
585 X 726 mm


46

Drafting tape


47

Pencils
• Wood pencils: H, 2H,
3H, 4H, 5H, 6H, 7H, 8H,
9H, B, HB, 2B, 3B, 4B,
5B, 6B.
• Semiautomatic Pencils
(lead holder) are more
convenient
then
ordinary wood pencils.


48

Eraser


49

Erasing Shield


50

Sharpener


51

T-square


52


53


54


55

Set-squares/triangles


56


57

Circle Template


58

Scales


59

Compass and divider


60

Sandpaper


61

Tissue paper


62

Clean paper


63

Introduction
Standards are set of rules that govern how technical
drawings are represented.
Drawing standards are used so that drawings convey
the same meaning to everyone who reads them.


65

Standard Code
Full name

Country

Code

Thailand
USA

มอก. สำำ นัก งำนมำตรฐำนผลิต ภัณ ฑ์
อุต สำหกรรม
American National Standard Institute
ANSI

Japan

JIS

Japanese Industrial Standard

UK

BS

British Standard

Australia

AS

Australian Standard

Germany

DIN

Deutsches Institut für Normung

ISO

International Standards Organization

66

Partial List of Drawing Standards
Contents

Code number
JIS Z 8311
JIS Z 8312

Sizes and Format of Drawings
Line Conventions

JIS Z 8313

Lettering

JIS Z 8314

Scales

JIS Z 8315

Projection methods

JIS Z 8316

Presentation of Views and Sections

JIS Z 8317

Dimensioning


67

Drawing Sheet
A4

Trimmed paper of
a size A0 ~ A4.

A3

Standard sheet size
(JIS)
A4
A3
A2
A1
A0

210 x 297
297 x 420
420 x 594
594 x 841
841 x 1189

(Dimensions in millimeters)

A2

A1

A0


68

Orientation of drawing sheet
1. Type X (A0~A4)
c

2. Type Y (A4 only)
d

Drawing space

c
Title block

c

Border
lines

d

Sheet size
A4
A3
A2
A1
A0

Drawing
space

Title block

c (min) d (min)
10
25
10
25
10
25
20
25
20
25


69

Drawing Scales
Length, size

Scale is the ratio of the linear dimension of an element
of an object shown in the drawing to the real linear
dimension of the same element of the object.
Size in drawing

Actual size

:


70

Drawing Scales
Designation of a scale consists of the word “SCALE”
followed by the indication of its ratio, as follow
SCALE 1:1

for full size

SCALE X:1 for enlargement scales (X > 1)
SCALE 1:X for reduction scales

(X > 1)

Dimension numbers shown in the drawing are correspond
to “true size” of the object and they are independent of
the scale used in creating that drawing.

71

Basic Line Types
Types of Lines

Appearance

Name according
to application

Continuous thick line

Visible line

Continuous thin line

Dimension line
Extension line
Leader line

Dash thick line

Hidden line

Chain thin line

Center line

NOTE : We will learn other types of line in later chapters.

72

Meaning of Lines
Visible lines represent features that can be seen in the
current view
Hidden lines represent features that can not be seen in
the current view
Center line

represents symmetry, path of motion, centers
of circles, axis of axisymmetrical parts

Dimension and Extension lines indicate the sizes and
location of features on a drawing

73

Types of Line


74

Line Conventions
•
•
•
•
•

•
•
•
•

Visible Lines – solid thick lines that represent visible edges or contours
Hidden Lines – short evenly spaced dashes that depict hidden features
Section Lines – solid thin lines that indicate cut surfaces
Center Lines – alternating long and short dashes
Dimensioning
– Dimension Lines - solid thin lines showing dimension extent/direction
– Extension Lines - solid thin lines showing point or line to which dimension applies
– Leaders – direct notes, dimensions, symbols, part numbers, etc. to features on
drawing
Cutting-Plane and Viewing-Plane Lines – indicate location of cutting planes for
sectional views and the viewing position for removed partial views
Break Lines – indicate only portion of object is drawn. May be random “squiggled” line
or thin dashes joined by zigzags.
Phantom Lines – long thin dashes separated by pairs of short dashes indicate alternate
positions of moving parts, adjacent position of related parts and repeated detail
Chain Line – Lines or surfaces with special requirements

75

Viewing-plane line
1
Extension
2
line

Dimension
3
Line

4
Center Line
Hidden Line
5
6
Break Line

Cutting-plane Line
7
8
Visible Line
9
10
Center Line (of motion)
Leader
Phantom
14
Line
13
Section Line
12
SECTION A-A

11
VIEW B-B
76

ABCDEFGHIJKLMNOPQRS
TUVWXYZABCDEFGHIJKL
MNOPQRSTUVWXYZABCD
EF

Lettering

ABCDEFGHIJKLMNOPQRS
TUVWXYZABCDEFGHIJKL
MNOPQRSTUVWXYZABCD

Text on Drawings
Text on engineering drawing is used :
To communicate nongraphic information.
As a substitute for graphic information, in those instance
where text can communicate the needed information
more clearly and quickly.
Thus, it must be written with
Legibility

- shape
- space between letters and words

Uniformity

- size
- line thickness

78

Example

Placement of the text on drawing
Dimension & Notes

Title Block

Notes

79

Lettering Standard
ANSI Standard

This course

Use a Gothic text style,

Use only a vertical Gothic

either inclined or vertical.

text style.

Use all capital letters.

Use both capital and
lower-case letters.

Use 3 mm for most

Same. For letters in title

text height.

block it is recommend to use
5~8 mm text height

Space between lines

N/A.

of text is at least 1/3

Follows ANSI rule.

of text height.

80

Basic Strokes
Straight

Slanted

Horizontal

Curved

Examples : Application of basic stroke
“I” letter

1

“A” letter 1

2

“B” letter 1

4

3

5

6

3
2

81

Suggested Strokes Sequence

Upper-case letters & Numerals
Straight line
letters

Curved line
letters
Curved line
letters &
Numerals

82

Suggested Strokes Sequence

Lower-case letters

The text’ s body height is about 2/3 the height of a capital
letter.

83

I

E

Stroke Sequence
T
F
L

H


84

Stroke Sequence
V

X

W


85

N

Y

Stroke Sequence
Z
M
K

A

4


86

Stroke Sequence
O

Q

C


G

87

D

R

Stroke Sequence
U
P
B

J

1


2

88

Stroke Sequence
5

7


89

S

8

Stroke Sequence
6
0
3

9


90

Stroke Sequence
l

i


91

v

Stroke Sequence
w
x
k

z


92

j

Stroke Sequence
y
f
t

r


93

c

d

Stroke Sequence
o
a
b

p

q


e

94

g

Stroke Sequence
n
m
h

u

s


95

Word Composition
Look at the same word having different spacing between letters.
A) Non-uniform spacing

JIRAPONG
B) Uniform spacing

J IR A P O N G
Which one is easier to read ?

96

Word Composition

Spacing
Contour

JIRAPONG
||
||

/

| )(

)|

|(

General conclusions are:
Space between the letters depends on the contour of
the letters at an adjacent side.
Good spacing creates approximately equal background
area between letters.

97

Example : Good and Poor Lettering
GOOD
Not uniform in style.
Not uniform in height.
Not uniformly vertical or inclined.
Not uniform in thickness of stroke.
Area between letters not uniform.
Area between words not uniform.

98

Sentence Composition
Leave the space between words equal to the space
requires for writing a letter “O”.

Example

ALL O DIMENSIONS O ARE O IN
MILLIMETERS O UNLESS
OTHERWISE O SPECIFIED.


99

Dimensioning Guidelines
The term “feature” refers to surfaces, faces, holes, slots, corners,
bends, arcs and fillets that add up to form an engineering part.
Dimensions define the size of a feature or its location relative to other
features or a frame of reference, called a datum.
The basic rules of dimensioning are:
1. Dimension where the feature contour is shown;
2. Place dimensions between the views;
3. Dimension off the views;
4. Dimension mating features for assembly;
5. Do not dimension to hidden lines;
6. Stagger dimensioning values;
7. Create a logical arrangement of dimensions;
8. Consider fabrication processes and capabilities;
9. Consider inspection processes and capabilities.

101

Important elements of dimensioning
Two types of dimensioning: (1) Size and location
dimensions and (2) Detail dimensioning


103

Geometrics
• The science of specifying and tolerancing
shapes and locations of features of on objects


104

Geometrics
• It is important that all persons reading a
drawing interpret it exactly the same way.
• Parts are dimensioned based on two criteria:
– Basic size and locations of the features
– Details of construction for manufacturing

• Standards from ANSI (American National
Standards Institute)


105

Scaling vs. Dimensioning
• Drawings can be a different scales, but
dimensions are ALWAYS at full scale.


106

Units of Measure
Angle
Dimensions

• Length
– English - Inches, unless
otherwise stated
• Up to 72 inches – feet and
inches over

– SI – millimeter, mm

• Angle
– degrees, minutes, seconds

107

Elements of a dimensioned drawing (Be familiar
with these terms


108

Arrangement of Dimensions
• Keep dimension off of the part where possible.
• Arrange extension lines so the larger dimensions are outside of the smaller dimensions.
• Stagger the dimension value labels to ensure they are clearly defined.

109

Dimensioning Holes

• Dimension the diameter of a hole.
• Locate the center-line.
• Use a notes and designators for repeated
hole sizes
110

Dimensioning the Radius of an Arc

Dimension an arcs by its radius.
Locate the center of the radius or two
tangents to the arc.
111

Drilled Holes, Counter bores and Countersinks

• Use the depth symbol to define the
depth of a drilled hole.
• Use the depth symbol or a section
view to dimension a counter bore.
• Countersinks do not need a section
view.
112

Angles, Chamfers and Tapers

• Dimension the one vertex for an angled face, the other vertex is determined by an

intersection.
• Chamfers are generally 45° with the width of the face specified.

113

Rounded Bars and Slots
• The rounded end of a bar or slot has a radius that is 1/2 its width.
• Use R to denote this radius, do not dimension it twice.
• Locate the center of the arc, or the center of the slot.

114

Limits of Size
• All dimensions have minimum and maximum values
specified by the tolerance block.
• Tolerances accumulate in a chain of dimensions.
• Accumulation can be avoided by using a single baseline.

115

Fit Between Parts
1. Clearance fit: The shaft maximum diameter is smaller than the hole minimum
diameter.
2. Interference fit: The shaft minimum diameter is larger than the hole maximum
diameter.
3. Transition fit: The shaft maximum diameter and hole minimum have an interference
fit, while the shaft minimum diameter and hole maximum diameter have a clearance
fit
Clearance Fit

Interference Fit

Transition Fit

116

Dimensioning standards

P. 117

Dimension text placement

P. 118

Unidirectional or aligned dimensioning?


119

Dimensioning Basic Shapes -Assumptions
•

•

Perpendicularity
– Assume lines that appear
perpendicular to be 90° unless
otherwise noted
Symmetry
– If a part appears symmetrical – it is
(unless it is dimensioned
otherwise)
– Holes in the center of a cylindrical
object are automatically located

121

Dimensioning Basic Shapes
• Rectangular Prism

122

• Cylinders
– Positive
– Negative

123

• Cone

Frustum

124

• Circle Pattern Center Lines


125

Grouping Dimensions
• Dimensions should always be placed outside
the part

Yes

No

126

Dimension guidelines
Dimensions should be placed in the view that
most clearly describes the feature being
dimensioned (contour (shape) dimensioning)


127

Maintain a minimum
spacing between the
object and the
dimension between
multiple dimensions.

A visible gap shall be
placed between the
ends of extension lines
and the feature to
which they refer.


128

Avoid dimensioning hidden
lines.

Leader lines for diameters
and radii should be radial
lines.


129

Where and how should we place dimensions
when we have many dimensions?


130

Where and how should we place dimensions
when we have many dimensions? (cont.)


131

Staggering Dimensions
• Put the lesser
dimensions closer
to the part.
• Try to reference
dimensions from
one surface
– This will depend
on the part and
how the
tolerances are
based.

132

Extension Line Practices


133

Repetitive Features

Use the Symbol ‘x’ to
Dimension Repetitive
Features


134

Symbols for Drilling Operations


135

References
•
•
•
•

T. Dragomatz
“Introduction to Engineering”, by Paul Wright
“Design Dimensioning and Tolerance”, by J. M.
McCarthy
Dr. Ashish K Darpe


136

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