Table of Contents
• Copy a Segment
• Copy an Angle
• Bisect a Segment (Perpendicular Bisector)
• Bisect an Angle

Copy a Segment
A B
1) Since a segment is a part of a
line, we’ll start by drawing a
ray that is somewhat longer
than our intended segment,
and call the starting point A’.
A’
2) Place the Needle end of the
compass on point A, and
adjust its length to match the
distance AB.
3) Without changing the width of
the compass, put the Needle
end of the compass on point
A’, and draw the arc to cross
your ray. Label the point of
intersection B’. You’ve just
copied AB to A’B’
B’

Copy An Angle
A
B
1) Since an angle is two rays with
a common vertex we’ll start by
drawing a ray and call ray
B’A’.
A’
2) Place the Needle end of the
compass on point B, and
make an arc that crosses over
from BA to BC.
3) Without changing the width of
the compass, put the Needle
end of the compass on point
B’, and draw the arc crossing
B’A’ long enough to more than
cross where B’C’ will be.
B’
C4) Now go back to the original
angle, and put your needle on
the point of intersection of AB
and the arc. Measure the
distance along the arc to the
ray BC.
5) Without changing the width of
the compass, put your needle
on the point of intersection of
the arc and B’A’. Make an arc
that crosses the first arc you
drew on this new angle.
6) Draw a ray from B’ thru the
point of intersection of the two
arcs. Label a point on the ray
as C’. You’ve copied the angle
ABC as A’B’C’.
C’

Bisecting a Segment
A B
1) Place the needle of your compass on A.
Make its width more than half-way to B,
and make a half-circle.
2) Without changing the width of the
compass, put the needle of your
compass on B. Make a half-circle that
overlaps the first one.
3) Draw a line that connects the two points
of intersection of the two half-circles.
That new line is both a bisector of the
segment AB, and is perpendicular to
AB.
4) Leave your construction marks to show
your work, and draw additional marks to
indicate both perpendicular AND
bisector.

Bisecting an Angle
A
B
1) Place the needle of your compass on B.
Draw an arc that crosses both BA and
BC.
3) Place the needle of the compass on D,
and set the width to match more than half
the distance to E. Make a half-circle.
5) Draw a line that connects the two points
of intersection of the two half-circles.
That new line is both a bisector of the
angle ABC.
C
D
E
2) Label the intersection of the arc and BA
“D”, and the intersection of the arc and
BC “E”.
4) Leave the compass width as it is. Place
the needle of the compass on E, and
make a half-circle overlapping the
previous half-circle.

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.

ISO International Standards Organization
Standard Code
ANSI American National Standard InstituteUSA
JIS Japanese Industrial StandardJapan
BS British StandardUK
AS Australian StandardAustralia
Deutsches Institut für NormungDINGermany
Country Code Full name
TS Turkish StandardTurkey

Drawing Sheet
Trimmed paper of
a size A0 ~ A4.
Standard sheet size
(ISO)
A4 210 x 297
A3 297 x 420
A2 420 x 594
A1 594 x 841
A0 841 x 1189
A4
A3
A2
A1
A0(Dimensions in millimeters)

Drawing space Drawing
space
Title block
d
d
c
c
c
Border
lines
1. Type X (A0~A4) 2. Type Y (A4 only)
Orientation of drawing sheet
Title block
Sheet size c (min) d (min)
A4 10 25
A3 10 25
A2 10 25
A1 20 25
A0 20 25

Drawing Scales
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
Length, size
:

Scale
• Scales are used to measure distances on
technical drawings.
• Types of scales
– Mechanical Engineers Scale (Fractional divisions)
– Civil Engineer’s Scale (Division of 10)
– Metric Scale
– Architectural Scale (Fractional divisions)
– Combination Scale

Mechanical Engineer’s Scale
• Mechanical Drawings are drawn in inches.
• 16 Divisions per inch
• Scales
– 1:1 Full Size
– 1:2 Half Size
– 1:4 Quarter Size
– 1:8 One Eight Size

Civil Engineer’s Scale
• Civil Drawings are drawn in feet as the base unit.
• Scales commonly used
– 1”:10’ 1”:100’
– 1”:20’ 1”:200’
– 1”:30’ 1”:300’
– 1”:40’ 1”:400’
– 1”:50’ 1”:500’
– 1”:60’ 1”:600’

Metric Scale
• Metric Mechanical Drawings are drawn in inches.
• Metric Civil Drawings are drawn in meters.
• Scale
– 1:1 Full Size
– 1:2 Half Size
– 1:5 Fifth Size
– 1:10 Tenth Size

Drawing Scale
• We use scale in drawing to represent objects
in the appropriate size on our drawing sheet.
– We can represent large objects on a B-Size sheet
using scale. (1” = 50’)
– We can represent small objects on B-Size Sheet
using scale. (4:1)
• What are some examples that you might want
to represent in a drawing?

Hidden Lines
• Dashed lines, lighter (thinner) than object
lines.
• Used in orthographic projection views to
represent edges that are “hidden” from the
line of sight for a view.
• Not used in isometric or oblique views.

Line Convention

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.

Visible lines represent features that can be seen in the
current view
Meaning of Lines
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

LINE CONVENTION
Precedence of coincide lines.
Hidden line drawing.
Center line drawing.

PRECEDENCE OF LINE
Visible
line
Order of
importance
Hidden
line
Center
line

Hidden arcs should start on a center line.
HIDDEN LINE PRACTICE

HIDDEN LINE PRACTICE
Hidden line should join a visible line, except it
extended from the visible line.
Correct
No !
Join
Leave
space

Correct No !
Hidden line should join a visible line, except it
extended from the visible line.
Leave
space
Leave
space
HIDDEN LINE PRACTICE

Hidden line should intersect to form L and T
corners.
Correct
No !
L T
HIDDEN LINE PRACTICE

CENTER LINE PRACTICE
In circular view, short dash should cross at the intersections of center line.
For small hole, center line is presented as thin continuous line.
Center line should not extend between views.
Leave space Leave space

Leave the gap when centerline forms a continuation with a visible or hidden
line
Leave
space
Leave
space
Leave
space
Leave
space
Center line should always start and end with
long dash.
CENTER LINE PRACTICE

Centerlines
Locate the center of circles and the axis
of cylindrical features.

Example : Line conventions in engineering drawing

PROJECTION
METHOD

PROJECTION METHOD
Perspective
Oblique Orthographic
Axonometric Multiview
Parallel

Types of Projection

Types of Projection

PROJECTION THEORY
The projection theory is based on two variables:
1) Line of sight
2) Plane of projection (image plane or picture plane)
The projection theory is used to graphically represent
3-D objects on 2-D media (paper, computer screen).

Line of sight is an imaginary ray of light between an
observer’s eye and an object.
Line of sight
Parallel projection
Line of sight
Perspective projection
There are 2 types of LOS : parallel convergeand

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

Orthographic
Projection

5
Orthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane
MEANING
Object views from top
Projection plane
1
2
3
4
51 2 3 4

ORTHOGRAPHIC VIEW
Orthographic view depends on relative position of the object
to the line of sight.
Two dimensions of an
object is shown.
Three dimensions of an object is shown.
Rotate
Tilt
More than one view is needed
to represent the object.
Multiview drawing
Axonometric drawing

Orthographic projection technique can produce either
1. Multiview drawing
that each view show an object in two dimensions.
2. Axonometric drawing
that show all three dimensions of an object in one view.
Both drawing types are used in technical drawing for
communication.
NOTES
ORTHOGRAPHIC VIEW

Axonometric (Isometric) Drawing
Easy to understand
Right angle becomes obtuse angle.
Circular hole
becomes ellipse.
Distortions of shape and size in isometric drawing
Advantage
Disadvantage Shape and angle distortion
Example

Multiview Drawing
It represents accurate shape and size.Advantage
Disadvantage Require practice in writing and reading.
Multiviews drawing (2-view drawing)Example

Perspective Projection
• Perspective – The most realistic of the
pictorial drawing styles because it is closest to
the way that we see.
– An ordinary photograph shows the view in
perspective.
• We will not cover this view in this class.
– You can study it on you own. See Chapter 16 in
you text.
– A drawing class would be another option.

Types of Parallel Projection
• Orthographic projections are a type of parallel
projection
– Orthographic (right angle) projections have
parallel projectors that are perpendicular (90
degrees) to the plane of projection
– In orthographic projection objects can be
presented at true size or scaled at a proportion of
their true size

Types of Orthographic Projection
• Multiview projection – A two dimensional
representation of a three dimensional object.
– It shows one or more necessary views of an object
• Front, Rear, Top, Bottom, Right or Left

MULTIVIEW PROJECTION
Three principle dimensions
of an object …
Width Depth
Height
Width
Height
Depth
Depth
… can be presented only
two in each view.
Adjacent view(s)
is needed to
fulfill the size
description.

1. Revolve the object with respect
to observer.
TO OBTAIN MULTIVIEW
REPRESENTATION OF AN OBJECT
2. The observer move around the
object.

Multi-view drawing

Multiview Drawings
First- and Third-Angle Projection
• There are two main systems used for
projecting and unfolding the views:
– Third-angle projection which is used in the United
States, Canada and some other countries
– First-angle projection which is primarily used in
Europe and Asia
• You should understand both methods

• Controls the placement of views
• Depicted on drawings by the truncated cone symbol
• Third Angle
• United States and Great Britain
• Top view - above front view.
• Right side - right of front view
• Same as “Glass box” unfolding
• First Angle
• Rest of world
• Top view - below front view.
• Right side - left of front view
• We will only use third-angle projections in EF101
Projection Types

Multiview Drawings
Third-angle Projection

Multiview Drawings
First-angle Projection

Isometric Drawings

Glass Box

Unfolding Glass Box

View
Relationships

OBSERVER MOVE AROUND
Front view Right side view
Top view

THE GLASS BOX CONCEPT
Bottom view
Left side view
Rear view

Height
Width
Depth
History

Orthographic
Projection
of Object Features

A
B
PROJECTION OF POINT(S)
AF
BR
AT
BF
AR
BT
AF AR
AT
BF
BR
BT
Equal
distance

A
B
AF BF BRAR
AT
BT
BR
AR
AF BF
AT
BT
True length
NORMAL LINE
True lengthPoint
Equal
length
PROJECTION OF LINE

A
B
AF BF BRAR
AT
BT
INCLINED LINE
Foreshortened
BR
AR
AF
BF
Foreshortened
AT
BT
True length
A
Equal
length
PROJECTION OF LINE

A
B
AF
BF BR
AR
AT
BT
OBLIQUED LINE
A
Equal
length
B
Foreshortened
Foreshortened
Foreshortened
BR
AR
AF
BF
AT
BT
PROJECTION OF LINE

B
C
A
PROJECTION OF PLANE
BF AF,CF CRAR,BR
AT
CT
NORMAL PLANE
Equal
length
Edge
Edge
True size
CR
AR,BR
AF,CF
BF
AT
BT
CT
BT

B
C
BF AF
CR
AR,BR
AT
CT
INCLINED PLANE
A
Equal
length
BT
C
CF
Edge
CR
AR,BR
Foreshortened
BT
CT
AT
AF
CF
Foreshortened
BF
PROJECTION OF PLANE

B
C
BF
AF
CR
AR
AT
CT
OBLIQUED PLANE
A
Equal
length
BT
C
CF
B
BR
Foreshortened
CR
AR
BR
AF
BF CF
Foreshortened
AT
BT
CT
Foreshortened
PROJECTION OF PLANE

PROJECTION OF OBJECT
The views are obtained by projecting all object features to the picture
plane.
You have to project the remaining surfaces which are
invisible too !

s
s
s
PROJECTION OF OBJECT

Freehand
Sketching

Straight Line
1. Hold the pencil naturally.
2. Spot the beginning and end points.
3. Swing the pencil back and forth between the points, barely
touching the paper until the direction is clearly established.
4. Draw the line firmly with a free and easy wrist-and-arm
motion

Horizontal line Vertical line

Nearly vertical
inclined line
Nearly horizontal
inclined line

Small Circle
Method 1 : Starting with a square
1. Lightly sketching the square and marking the mid-points.
2. Draw light diagonals and mark the estimated radius.
3. Draw the circle through the eight points.
Step 1 Step 2 Step 3

Method 2 : Starting with center line
Step 1 Step 2 Step 3
1. Lightly draw a center line.
2. Add light radial lines and mark the estimated radius.
3. Sketch the full circle.
Small Circle

1. Place the little finger (or pencil’ s tip) at the center as a
pivot, and set the pencil point at the radius-distance from
the center.
2. Hold the hand in this position and rotate the paper.
Large Circle

Arc
Method 1 : Starting with a square
Method 2 : Starting with a center line

Steps in Sketching
1. Block in main shape.
2. Locate the features.
3. Sketch arcs and circles.
4. Sketch lines.

Example