Engineering Drawing First Edition

ENGINEERING DRAWING
EXERCISE

1. What are different types of lines and their styles? Write their uses.
2. By using geometry method, draw a pentagon inscribed a circle with radius of

5mm.
3. By using geometry method, draw a hexagon inscribed a circle with radius of

6mm.
4. By using geometry method, draw an ellipse as figure below:

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ENGINEERING DRAWING

Chapter 3.0 Orthographic Projection and Isometric
Working drawings usually include a three-dimensional view (or views) of the part or
assembly as needed (but it is not a must). An axonometric view is a view in which an
object appears to be rotated to show its all three dimensions. Axonometric views are
classified according to how the axes are oriented into Isometric, Diametric and Trimetric.
Isometric View - In isometric views the
two edges of the view make 30⁰ angles
with the horizontal and that makes the
three angles between the view axes to be
equal to 120⁰.

Diametric View - In diametric views the
angles may vary but two of the three
angles between the view axes are equal.

Trimetric View – In trimetric views all
three angles between view axes are
different.

Orthographic Projection

Orthographic projection (or orthogonal projection) is a means of representing a three-
dimensional object in two dimensions. A multi-view orthographic projection is an
illustration technique in which up to six pictures of an object are produced (usually three
are sufficient in most cases or two in some cases), with each projection plane being
perpendicular to one of the coordinate axes of the object.

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Views of Orthographic Projection.
Following views are formed of an object in Orthographic Projection.

i. Front View - This view is prepared by placing the object in front. The length
and height of an object are shown in this view.

ii. Top View - This view is prepared by looking to the object from the upper
side. The length and breadth of the object are shown in it.

iii. Side View - This view is prepared by looking to the object from the right side
or left side. The breadth and height of the object are shown in it

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The views are positioned relative to each other according to either of two schemes:

First-Angle Projection: In first-angle projection the object is conceptually located in
quadrant I (i.e., it floats above and before the viewing planes), the planes are opaque,
and each view is pushed through the object onto the plane furthest from it. By taking the
Front view on the frontal plane, top view on the horizontal plane and side view on the
Profile plane, the planes are then straightened by rotation. In this way, the front view
comes over the top view; side view comes beside the front view.

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Characteristics of First Angle Projection:
i. Front view always comes over the top view.
ii. Top view always comes under the front view.
iii. Right side view always comes to the left at the front view.
iv. Left side view always comes to the right of the front view.
v. The view is always in opposite direction to the observer.
vi. The object is always in the middle of the view and the observer.

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Examples of First Angle Projection:

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Third-Angle Projection: In third-angle projection the object is conceptually located in
quadrant III (i.e., it is positioned below and behind the viewing planes), the planes are
transparent, and each view is pulled onto the plane closest to it. front view forms on the
frontal plane, top view forms on the horizontal plane and side view forms on the profile
plane. After making the views, the planes are set straight by rotation. In this way, the top
view comes over the front view, while side view forms by the side of front view.

Characteristics of Third Angle Projection:
i. Top view always comes over the Front view.
ii. Front view always comes under the top view.
iii. Right side view always comes to the right of the front view.
iv. Left side view always comes to the left of the front view.
v. The view is always formed to the side of the observer.
vi. The view is always in the middle of the object and the observer.

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Examples of Third Angle Projection:

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A standard projection symbol is used in drawings to identify the projection system of the
orthographic views.

Following rules should be followed while forming orthographic drawing.
i. Front view and top view always form over/under each other.
ii. The front view shows the length and height of an object.
iii. The side view shows the breadth and height of an object.
iv. The top view shows the length and breadth of an object.
v. Side view always forms beside the front view.
vi. Projection line always forms by the meeting of two surfaces.

vii. The hidden detail of an object is always shown by dotted line.

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Isometric Drawing
An isometric drawing is a type of 3D drawing that is set out using 30-degree angles. It's
a type of axonometric drawing in which the same scale is used for every axis, resulting in
a non-distorted image. Isometric grids are relatively easy to set up, and once you've
mastered the basics of isometric drawing, creating a freehand isometric sketch is quite
straightforward.
An isometric drawing is a 3D representation of an object, room, building or design on a
2D surface. One of the defining characteristics of an isometric drawing, compared to other
types of 3D representation, is that the final image is not distorted. This is due to the fact
that the foreshortening of the axes is equal. The word isometric comes from Greek to
mean 'equal measure'.

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In an isometric drawing, the object appears as if it is being viewed from above from one
corner, with the axes being set out from this corner point. Isometric drawings begin with
one vertical line along which two points are defined. Any lines set out from these points
should be constructed at an angle of 30 degrees.
The example below has been drawn with a 30 degree set square. Designs are always
drawn at 30 degrees in isometric projection. It is vital that drawing equipment such as T-
squares and 30/60 degree set squares are used carefully. The drawing paper should be
clip securely to a drawing board.

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Step 1: Draw two basic 30 degree guidelines, one to the left and one to the right, plus a
vertical guideline in the center of the drawing. In this example three edges of the cube
have been drawn over the guidelines (they are slightly darker)

Step 2: Draw guidelines to help you start constructing the left and right sides of the
cube. Remember to use a 30 degree set square for the 'angled' lines.

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Step 3: Complete the top of the cube by projecting lines with the 30 degree set square
as shown below.

Examples of Isometric Drawing:

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EXERCISE

1. From figure below, draw third angle projection consists of Top View, Side View &
Front View. (Dimension in mm)

2. From figure below, draw third angle projection consists of Top View, Side View &
Front View. (Dimension in mm)

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ENGINEERING DRAWING
3. From figure below, draw third angle projection consists of Top View, Side View &

Front View. (Dimension in mm)

4. Draw isometric drawing based on the figure below: (Dimension in mm)

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5. Draw isometric drawing based on the figure below: (Dimension in mm)

6. Draw isometric drawing based on the figure below: (Dimension in mm)

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ENGINEERING DRAWING
Chapter 4.0 Geometric Dimensioning and Tolerance
Dimensioning is the process of defining the size, form and location of geometric features
and components on an engineering drawing. Before an object can be built, complete
information about both the size and shape of the object must be available. The exact
shape of the part or assembly is shown by the different views in the drawing sheet.
Dimensions are added to the two- dimensional views (not to the 3D view) in the drawing
sheet such that it will show all the size and location details of the part.
In metric drawings, generally, dimensions are in millimeters. To avoid having to specify
'mm' after every dimension, a label such as 'all dimensions in mm' or 'unless otherwise
stated all dimensions are in mm' is usually contained in the title block. If the dimension is
less than one a leading zero should be used before the decimal point (e.g., 0.5).
Dimensions used in drawings can be categorized as:

• Size dimensions - define size of features (radius, diameter, length, width,
thickness, etc).

• Location dimensions - define location of part features (such as holes).
Extension (or projection) lines are used to indicate the extremities of a dimension. They
are generally drawn up to 1 mm from the outline of the object. Dimension line are used to
label a particular dimension. They have one or more arrowheads.

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Dimensions are usually placed between extension lines. But when there is no enough
room to accommodate the dimension, either the dimension value or the dimension lines
can be located outside extension lines as illustrated.

Dimensions may be divided into three different types; Linear dimensions, Angular
dimensions, and Leader dimensions.

i. Linear Dimensions - they are either horizontal or vertical to the
dimensioning plane.

ii. Angular Dimensions - they are usually specified in decimal degrees (e.g.,
27.5°). Also they can be specified using degrees and minutes or degrees
minutes and seconds (e.g., 27°30' or 0°15'40").

iii. Leader Dimensions - they are usually used to specify a diameter or a radius
where a leader line is used to point towards the feature being dimensioned.

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Two methods of dimensioning are in common use.
i. Unidirectional - The dimensions are written horizontally.
ii. Aligned - The dimensions are written parallel to their dimension line. Aligned
dimensions should always be readable from the bottom or the right of the
drawing.

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Chain Dimensioning (dimensioning from feature to feature) is commonly used and easy
to insert. Chains of dimension should only be used if the function of the object won't be
affected by the accumulation of the tolerances.
Baseline (or Ordinate) Dimensioning is used when the location of features must be
controlled from a common reference point or plane. It is used to ensures that tolerances
(or errors) in manufacturing do not add up.

Some of the most important rules for dimensioning are as follows:
• Dimension figures should never be crowded or in any way that make them difficult

to read.

• Each feature should be dimensioned.

• Dimensions should be placed outside the part when possible.

• Dimensions should be evenly spaced and grouped.

• Dimensions should not be duplicated or the same information given in two different

ways (except when dual dimensioning is to be used) and no dimensions should be

given except those needed to produce or inspect the part.

• Dimensions should be placed in the views where the features being dimensioned

are shown in true shape.

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• Dimensioning to hidden lines should be avoided wherever possible (section views
may be used to show the shape and dimensions of internal features).

• The longer dimensions should be placed outside all intermediate dimensions so
that dimension lines will not cross extension lines.

• Dimension lines should not cross, if avoidable.
• Dimension lines and extension lines should not cross, if avoidable (extension lines

may cross each other).
• Extension lines and object lines should not overlap.
• Detail dimensions should "line up" in chain fashion.
• Leaders should slope at 45°, or 30°, or 60° with horizontal but may be made at any

convenient angle except vertical or horizontal.
• Center lines or marks should be used on all circles and arcs.
• In general, a circle is dimensioned by its diameter, an arc by its radius.
• Cylinders should be located by their center lines.
• Cylinders should be located in the circular views, if possible.
• A cylinder is usually dimensioned by giving both its diameter and length in the

rectangular view when possible.

Tolerance

Tolerance is the total amount a dimension may vary and is the difference between the
upper (maximum) and lower (minimum) limits. Tolerances are used to control the amount
of variation inherent in all manufactured parts. In particular, tolerances are assigned to
mating parts in an assembly.

One of the great advantages of using tolerances is that it allows for interchangeable parts,

thus permitting the replacement of individual parts. Tolerances are used in production

drawings to control the manufacturing process more accurately and control the variation

between parts.

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Tolerance representation

Direct limits or as tolerance values
applied directly to a dimension

Geometric tolerances

Notes referring to specific condition.

Geometric Dimensioning and Tolerancing (GDT)
GDT is a method of defining parts based on how they function, using standard
ASME/ANSI symbols. Within the last 15 years there has been considerable interest in
GDT, in part because of the increased popularity of statistical process control. This control
process, when combined with GDT, helps reduce or eliminate inspection of features on
the manufactured object. The flipside is that the part must be tolerance very efficiently;
this is where GDT comes in. Another reason for the increased popularity of GDT is the

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rise of worldwide standards, such as ISO 9000, which require universally understood and
accepted methods of documentation.

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Example:

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EXERCISE

1. State the definition of ‘dimensioning’.
2. Explain TWO (2) methods of dimensioning.
3. Explain the importance of tolerance in engineering.
4. Sketch FIVE (5) examples of GDT symbols and their meaning.

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ENGINEERING DRAWING

Chapter 5.0 Sectional View

When an object becomes more complex, as in the case of an automobile engine block, a
clearer presentation of the interior can be made by sketching the object as it would look
if it were cut apart. In that way, the many hidden lines on the sketch are eliminated. The
process of sketching the internal configuration of an object by showing it cut apart is
known as sectioning.

Section views are used to reveal interior features of an object that are not easily
represented using hidden lines in order to improve the visualization of parts or
assemblies. Traditional section views are based on the use of an imaginary cutting plane
that cuts through the object to reveal interior features. Section views are used in multi-
view drawings in order to help in clarifying the drawings and to facilitate the dimensioning
of drawings.

The figure shows a regular multi-view drawing and a sectioned multi-view drawing of the

same part in the front view, the hidden features can be seen after sectioning.

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Hatching lines inclined at 45⁰ are used to represent the new surfaces that are introduced
by the section. The hatching lines spacing vary from 1.5mm for small sections to 3mm for
large sections. In some cases, the hatching may be used to indicate the material where
different standardized hatching patterns are used for identifying different materials.

A surface cut by the saw in the drawing is a cutting plane. Actually, it is an imaginary
cutting plane taken through the object, since the object is imagined as being cut through
at a desired location.

A cutting plane is represented on a drawing by a cutting plane line. The cutting plane is
shown in orthogonal view as a cutting line (a double dashed chain line is used) with two
arrows that point towards the portion of the object that will be kept. Sections are usually
designated by uppercase letters.

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ENGINEERING DRAWING
Here is a graphic example of a cutting plane line and the section that develops from it.

It is important to note that hidden lines should not be shown in section views, as seen in
the figure. Multiple sections can be used in multi-view drawings when needed, as seen in
the figure.

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ENGINEERING DRAWING
Section View Types
Different types of section views are used in technical drawing where the type of section
to be used depends on the shape of the object to be sectioned and the internal features
to be revealed by the section.

i. Full Section

▪ A full section view is made by passing an imaginary cutting plane fully

through an object.

▪ The figure shows an imaginary cutting plane passing fully through an object

and half of it being removed.

▪ The section may cut the object in the middle or at any desirable location.
▪ In a multi- view drawing, a full section view is placed in the same position

that an un-sectioned view would normally occupy; that is, a front section
view would replace the traditional front view.

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ii. Half Section

▪ A half section is made by passing two perpendicular imaginary cutting

planes halfway through an object such that one quarter of the object is
removed.

▪ Hidden lines are omitted on both halves of the section view.
▪ External features of the part are drawn on the un-sectioned half of the view.
▪ A center line, not an object line, is used to separate the sectioned half from

the un-sectioned half of the view.

▪ Half section views are most often used on parts that are symmetrical, such

as cylinders.

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iii. Broken-out Section

▪ A broken-out section is used to show interior features of a part by breaking

away some of the object.

▪ A broken-out section is used instead of a half or full section view to save

time.

▪ A break line separates the sectioned from un-sectioned portion of the view.
▪ A jagged break line is drawn to represent the edge of the break.
▪ No cutting plane line is drawn for the broken-out section view.
▪ Unlike half sections, hidden lines are shown in the un- sectioned portion of

the view.
iv. Offset Section

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▪ An offset section has its cutting plane bent at 90 degree angles to pass

through important features.

▪ Offset sections are used for complex parts that have a number of important

features that cannot be sectioned using a straight cutting plane.

▪ It should be noted that the edges resulting from bending the cutting plane

are not shown in the sectional view.
v. Aligned Section

▪ Aligned sections are special types of orthographic drawings used to revolve

or align special features of parts to clarify or make them easier to represent
in section.

▪ Two intersecting planes (the angle between them is more than 90 degrees)

are used for sectioning.

▪ The sectioned surfaces resulting from the two cutting planes are aligned

together along one plane.

▪ Normally the alignment is along a horizontal or vertical cutting plane.

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ENGINEERING DRAWING
EXERCISE

1. State the definition of sectioning.
2. From the figure below, construct the front view with offset sectioning (according to

cutting plane C-C).

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3. From the figure below, construct the orthographic view (front view, top view, side

view) with FULL sectional view (according to cutting plane A-A)

A
A

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REFERENCES

Parthasarathy, N.S & Murali, V (2015). Engineering Drawing. Oxford University Press.
MALAYSIAN STANDARD (2009) Technical Drawings - Indication of Dimensions and

Tolerances - Part 1: General Principles (ISO 129-1:2004, Idt). Department of
Standards Malaysia.
Simmons, C. & Maguire, D. (2012). Manual Engineering Drawing.
R. K. Dhawan, R.K (2011). Fundamental of Engineering Drawing. S. Chand Publishing.
K Vendata Reddy (2010). Textbook of Engineering Drawing. BS Publications.
Shiv Kumar (2016). Engineering Graphics. Tech India Publication.

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