Basic introduction to Engineering Drawing

Engineering Drawing – MEng2011
Chapter 1
Introduction to Basic Engineering Drawing
Debre Berhan University
College of Engineering
Department of Mechanical Engineering
By Tariku D.
Thermal Engineering
February 2021

Outline
 Introduction
 Classification of drawing
 Instruments
 Scale
 Alphabets of lines
 Title block
 lettering
College of Engineering, Department of Mechanical Engineering, Prepared by Mr. Tariku Dessie

s
Introduction
1. How are you going to explain an object in words?
2. How much words do you need to explain the object
completely?
3. How much you are efficient in transferring and
conveying information regarding to the object?
 These three main questions raise the development of
Engineering drawing
1

What is drawing?
Drawing is a universal communication media through
which ideas and thoughts are conveyed from one person
to another.
It is the art of representation of an object by systematic
lines.
 Also it is a graphical language to exchange ideas so it is a
means of communication.
It is used for:-Design, construction, maintenance,
installation, etc.
College of Engineering, Department of Mechanical Engineering, Prepared by Mr. Tariku Dessie 2

• Drawing is distinctively classified into two major classes known as:
1. Artistic drawing (Free hand)
2. Engineering drawing (Instrumental drawing)
Artistic drawing:
 It gives more emphasis to esthetic value of the object
 It is used to express beauty, imaginations and abstract ideas
Engineering drawing:
 It is a universal communication media through which ideas and
thoughts are conveyed from one person to another.
 It is a language which uses lines, symbols, dimensions and notations
to accurately describe the form, size, kind of material and finish of a
product or a construction.
 It is prepared by using drawing instrument.
Classification of drawing
3

Types of Technical/Engineering Drawings
Three Basic Types:
1. Freehand sketches/Drawing
 The lines are sketched without using instruments other
than pencils and erasers.
Example
4

2. Instrument drawing
 Instruments are used to draw straight lines, circles, and
curves concisely and accurately. Thus, the drawings are
usually made to scale.
Example
5

a
3. Computer aided drawing
 The drawings are developed by and usually made by
commercial software such as AutoCAD, CATIA,
SOLIDWORKS, ANSYS, ProEngineer, etc.
Example
8
6

 Based on the dimension of the object
1. Plane geometrical drawing
 It is art of representation of objects having two dimensions such as rectangle,
square ellipse and etc.
2. Solid geometrical drawing
 It is art of representation of objects having three dimensions such as prism, cube,
cone, cylinder, sphere and etc.
 Based on Engineering profession drawing can be divided into the following:-
1. Mechanical Engineering drawing or machine drawing
- It is art of representation of mechanical engineering objects such as machines and
machine parts, automobiles, airplanes, ships and etc.
2. Civil Engineering drawing
- It is art of representation of civil engineering objects such as roads, buildings,
bridges, dams and etc.
3. Electrical and Electronic engineering drawing
 It is the art of representation of electrical objects such as electronic circuits,
motors, generators, poles, towers, transformers, wiring diagrams and etc.

Principles of Drawing
There are two principles in drawing:-
 Visualization
The ability to see what an object looks like in the mind
of eye.
 Implementation
Drawing of an object that has been visualized.

Elements of Engineering Drawing
Engineering drawing are made up of graphics language
and word language.
Graphics
language
Describe a shape
(mainly).
Word
language
Describe size, location and
specification of the object.
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Drawing Instruments
Drawing Instruments
• In engineering drawing any object is represented by straight lines
and/or curves. These lines should be drawn as accurate as possible
by the help of drawing instruments.
• Quality of a drawing depends to a large extent on the quality ,
adjustment, proper use and care of drawing instruments.
10

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Cont.…
List of drawing instruments
 Drawing board
 T-square
 Drawing sheets
 Drafting pencils
 Pencil sharpener
 Lettering instrument
 Eraser
 Erasing shield
 Triangle (Set-square)
(450 and 300 - 600)
 French curve
 Drawing instrument set
(Compass, Divider,
extensions)
 Protractor
11

T
Drawing board
 Drawing tables come in many different size
and design. It could be fixed, movable,
adjustable, etc.
 They are used to attach drawing sheet.
Note that:-
 Keep your drawing table clean and dry not
to affect your drawing quality.
 Don’t use blades to cut drafting tapes on
drawing table.
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T-Square
 They can be made from different materials, mostly from wood
or plastics.
 Parts: blade and head
 Two edges of the blade should be parallel.
 The head is fixed at 900 to the blade
 The cleanness of your T –square greatly affect your drawing
quality and cleanliness.
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Drawing sheet
 Made from different materials with different quality.
 Paper, tracing paper, vellum, tracing cloth, glass cloth or film.
 Drawing sheets will determine selection of pencil grade.
Standard drawing sheet size
A5 148 x 210 mm
A4 210 x 297 mm
A3 297 x 420 mm
A2 420 x 594 mm
A1 594 x 841 mm
A0 841 x 1189 mm
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Drawing space Drawing
space
Title block
d
d
c
c
c
Border
lines
1. Type X (A0~A3) 2. Type Y (A4 only)
Orientation of drawing sheet
Title block
Sheet size c (mm) d (mm)
A4 5 20
A3 5 20
A2 5 20
A1 10 20
A0 10 20
c
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Set square/triangles
 Inclined lines are drawn at standard angles using the 45º x
45º and the 30º x 60º triangles.
 Used to draw parallel and perpendicular lines accordingly.
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Drawing pencils
 Most drawing pencil leads are made from graphite
and mixture of varying quantity of clay.
• 6B(softest and blackest)
• 5B(extremely soft)
• 4B extra soft)
• 3B (very soft)
• 2B (soft, plus)
• B (soft)
• HB (medium soft)
• F (intermediate, between
soft and hard)
• H (medium hard)
• 2H (hard)
• 3H (hard, plus)
• 4H (very hard)
• 5H (extra hard)
• 6H (extra hard, plus)
• 7H (extremely hard)
• 8H (extremely hard,
plus)
• 9H (Hardest)
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20
 Selection of drawing pencil
 Type and quality of drawing paper
 How thick and dark you want the line to be.
 Pencil lines should be clean and sharp. They must be dark enough for the
views to be seen when the standard lines are drawn.
 If you use too much pressure, you will groove the drawing surface. You can
avoid this if you use proper grade of lead.
 Semi-automatic Pencils (having lead holder) are more convenient than
ordinary wood pencils.
18

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Protractors
 Are used for measuring and laying off angles other than those that
may be drawn by set squares.
 Protractors are used to mark or measure angles between 0 -1800
(half circle) and 0 - 3600 (full circle).
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Compass and divider
 Compass : Used to draw circles and arcs.
 For a small circle, standard ( bow) compass is used.
 For a large circle beam compass are used
Distances are subdivided and measurements are transferred with
dividers.
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Eraser
• Extra lines and lines drawn by mistake are canceled
by using eraser made of rubber material.
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Templates
 Saves a great deal of time.
 Helps to draw circles, ellipses, squares, bolts heads, nuts,
electrical symbols, architectural symbols, plumbing symbols and
so on (of smaller size).
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French Curve
 Also called irregular curves
 Used to draw curves other than circles and circular arcs.
 French curves are used to draw irregular curves which are
impossible to draw using compass.
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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
:
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Cont.….
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)
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Alphabet of Lines
 Alphabet of lines is the list of lines symbols, used to
represent the shape and describe the size of an object.
 Each lines is drawn at different thickness or darkness
for contrast.
 The weight of the line refers to its thickness or width.
 Lines are divided into three weights: thick, medium
thick and thin lines.
26

Types of lines
27
1. Construction lines:
 Thin lines, used to lay out drafting sheets and drawing;
 4H to 6H pencil with a sharp, conical point should be used.
2. Visible or Object lines:
 Are solid and thick lines, used to indicate visible surfaces and
edge of an object or a view.
 2H or B are used.

3. Hidden lines:
 Used to indicate interior or inside edges, non-visible surfaces
and hollow areas of an object;
 Are medium weight short dashes and drawn with 1mm gaps and
3mm long dashes;
 2H lead is used.
4. Centre lines:
 Used to indicate the centre of circle, arc, or any symmetric
object;
 Are thin lines, consisting of alternating and evenly spaced long
and short dashes, with long dashes at each ends;
 At intersection point, centre lines should be drawn as short
dashes;
 4H lead is used.
3mm
1mm
3mm
1mm
18-36mm
28

5. Symmetry lines:
 Are used when partial view of symmetrical parts are drawn;
 It is a centre line with two thick short parallel lines drawn at right angels to it
at both sides;
 4H lead is used.
6. Extension lines:
 Are thin and unbroken lines
 Are used to extend dimensions beyond the outline of view.
 They are drawn parallel to each other and perpendicular to distance to be
shown/dimension lines;
45mm
Dimension Line
Extension Line
leader line
29

7. Dimension lines:
 Thin unbroken lines, inserted between each pair of extension
lines to define the size and location;
 All arrow heads in a drawing should be uniform in size and
style;
 Leader lines: Medium line with arrowhead to show notes or
label for size or special information about a feature.
 4H to 6H pencil with a sharp, conical point should be used
 Leader lines are also used for dimensioning features of an
objects.

8. (a) Viewing Plane lines:
 Are thick lines, used to indicate the direction of the plane from which a surface is
viewed;
 2H or B are used.
(b) Cutting Plane lines:
 Used to indicate the location of cutting plane from which a sectional view is taken;
 Dark thick lines and composed of one long and two short dashes spaced alternatively;
 They can also be drawn composed of equal dashes approximately 6mm long and
1.5mm gap between dash;
Gap=1.5mm
Short dash=3mm
Long dash=18 to 36mm
Gap=1.5mm
dash=6mm
A
A
A
A
OR
31

9. Section lines:
 Thin lines, used to show the cut surface of an object in sectional view;
 Should be equally spaced and proportional to the mass of the sectioned surface;
 2H is used.
10. Break lines:
 Are used to shorten the view of long uniform sections or to show partial section
views;
 2H or B are used.

11. Phantom lines:
 Thin lines used to indicate an alternate position of a moving part,
adjacent position of related parts, and repetitive detail;
 The part in one position is drawn in full lines, while in the
alternative position, it is drawn with phantom lines;
12. Chain lines:
 Consisting of thick, alternating long and short dashes
 Show that a surface or surface zone receive additional treatment;
 4H to 6H pencil with a sharp, conical point should be used.
Long dash=10-20mmm
Short dash= 3mm
Gap=1.5mm
Long dash=18-36mmm
Short dash= 3mm
Gap=1.5mm
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Example : Line conventions in engineering drawing
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Title Block
 The title block is part of the drawing on which different descriptions
of the drawing are written.
 Different companies and organizations may have their own style of
title block.
The conventional one includes the following:
1. Title of Drawing
2. Drawing number
3. Scale of drawing
4. Method of projection
5. Name of the firm
6. Initials of the Staff who have designed, checked and approved.
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Precedence of Lines
 When a visible line coincide with a hidden line or center
line, draw the visible line. also, extend the center line
beyond the outlines of the view.
 When a hidden line coincides with a center line, draw the
hidden line.
 When a visible line coincides with a cutting plane, draw
the visible line.
 When a center line coincides with a cutting plane, draw
the center line and show the cutting plane line outside the
outlines of the view at the ends of the center line by thick
dashes.
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Dimensioning
 The expression of the features on a drawing, using lines, symbols,
figures and notes.
Principles of Dimensioning
• All dimensional information necessary to describe a component
clearly and completely shall be written directly on a drawing.
• Features shall be dimensioned once only on a drawing not be
repeated in another view.
• Dimension should be placed on the view where the shape is best
seen.
• Dimensions should be placed outside the view
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• Dimensions should be taken from visible outlines rather than from
hidden lines.
• Dimensions should be expressed in one unit only preferably in
millimeters, without showing the unit symbol (mm).
Arrangement of Dimensions
Dimensions are arranged in 3 ways:-
 Chain dimensioning
 Parallel dimensioning
 Combined dimensioning.
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LETTERING
 A drawing without ‘lettering’ would only communicate the
appearance and shape of an object.
 The size of the object, the location of features and the materials
needed to make the object can only be expressed by words which
must be lettered in a clear and uniform style.
 Gothic style is the standard style of lettering for engineering
drawing.
There are two types of lettering:-
 Vertical lettering and
 Inclined lettering (67.5 degree from horizontal)
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Rules for lettering
1. Use single stroke, vertical, evenly spaced gothic
lettering
2. Use upper case letters only
3. Always skip a space b/n rows of words about 3mm
4. Uniform lettering height (normal lettering height is 2.5,
3.5, 5, 7 mm)
5. Use very light guide lines
 lettering composition means arrangements of
words and lines with letters of the right style and
size.
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Basic Strokes
Straight Slanted Curved
Horizontal
1 1 2
3
Examples : Application of basic stroke
“I” letter “A” letter 1
2
3
4 5
6
“B” letter
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Suggested Strokes Sequence
Straight and
inclined line
letters
Curved line
letters
Curved line
letters &
Numerals
Upper-case letters & Numerals
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Stroke Sequence
I L T F
E H
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 The text’ s body height is about 2/3 of the height of a
capital letter.
Suggested Strokes Sequence
Lower-case letters
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Stroke Sequence
j y f t
r
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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.
Example : Good and Poor Lettering
48

Basic introduction to Engineering Drawing

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