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

E2) 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

spaceTitle block

d

d

c

c

cBorder

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 AppearanceName 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

Hiddenline

Center

line

Hidden arcs should start on a center line.

HIDDEN LINE PRACTICE

HIDDEN LINE PRACTICE

Hidden line should join a visible line, except itextended from the visible line.

Correct

No !

Join

Leavespace

Correct No !

Hidden line should join a visible line, except itextended from the visible line.

Leavespace

Leavespace

HIDDEN LINE PRACTICE

Hidden line should intersect to form L and Tcorners.

Correct

No !

L T

HIDDEN LINE PRACTICE

CENTER LINE PRACTICEIn 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

Leavespace

Leavespace

Leavespace

Leavespace

Center line should always start and end with

long dash.

CENTER LINE PRACTICE

CenterlinesLocate 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 dimensionsof an object …

Width Depth

Height

Width

He

igh

t

Depth

De

pth

… can be presented onlytwo in each view.

Adjacent view(s)

is needed to

fulfill the sizedescription.

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 DrawingsFirst- 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 DrawingsThird-angle Projection

Multiview DrawingsFirst-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

De

pth

History

Orthographic

Projection

of Object Features

A

B

PROJECTION OF POINT(S)

AF

BR

AT

BFAR

BT

AFAR

AT

BFBR

BT

Equaldistance

A

B

AF BF BRAR

AT

BT

BR

AR

AF BF

AT

BT

True length

NORMAL LINE

True lengthPoint

Equallength

PROJECTION OF LINE

AB

AF BF BRAR

AT

BT

INCLINED LINEForeshortened

BR

AR

AF

BF

Foreshortened

AT

BT

True length

A

Equallength

PROJECTION OF LINE

AB

AF

BF BR

AR

AT

BT

OBLIQUED LINE

A

Equallength

B

ForeshortenedForeshortened

Foreshortened

BR

AR

AF

BF

AT

BT

PROJECTION OF LINE

BC

A

PROJECTION OF PLANE

BF AF,CF CRAR,BR

AT

CT

NORMAL PLANE

Equallength

EdgeEdge

True size

CR

AR,BR

AF,CF

BF

AT

BT

CT

BT

BC

BF AF

CR

AR,BR

AT

CT

INCLINED PLANE

A

Equallength

BT

C

CF

Edge

CR

AR,BR

Foreshortened

BT

CT

AT

AF

CF

Foreshortened

BF

PROJECTION OF PLANE

BC

BF

AF

CR

AR

AT

CT

OBLIQUED PLANE

A

Equallength

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 areinvisible 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