Bangladesh University of Business and Technology

Department of Textile Engineering

MEC 102
Engineering Drawing Lab

Laboratory Manual

January 2020
 Preface

The purpose of this manual is to guide the students for the engineering drawing lab course. This
course is designed to make the students familiar with different techniques of engineering drawing,
drafting tools and their operations. Typically, engineering drawing is used among engineers to
convey information about different machine parts and objects. Moreover, various engineering
drawing of machine structure and machine parts are depicted in the textbooks. It is hoped that, a
basic knowledge about drafting tools, orthographic and isometric drawings, sectional drawings
will be gained by the students after completion of this course.
General Information:
Course Code: MEC 102.
Course Title: Engineering Drawing Lab.
Credit Hour: 1.5.
Contact Hour: 3 Hours per week.
Full Marks: 100.
Lab Room: B3/401 (Building 3).

Lab Rules and Regulations:

1. Attend the classes with full preparation.
2. Bring this manual every time you come to the lab.
3. Keep your drawing sheet clean.
4. Follow all the safety instructions in the lab.
5. Assignments should be prepared according to the instruction given. Assignments should be
submitted on due date, failure to this may result in number deduction.
6. Perform every experiment with utmost attention and sincerity. No horseplay is allowed.
7. Make sure to bring all the necessary instruments.
8. Make sure that each drawing table has required free space surrounding it.
9. Do not cause disturbance to other students’ drawing.
10. Attend all the viva, quizzes and lab exams for being eligible to get full grade.
Safety Rules:
1. Keep hands and tools wiped clean and free of dirt, oil and grease.
2. Do not carry sharp tools on pockets.
3. Do not keep working tools at the edge of the table.
4. Tools that are not being used should always be kept at their proper places.
5. Protect your eyes from any debris and sharp objects.
6. Turn on enough light bulbs to ensure sufficient light in the room.
7. Always turn off the bulbs and fans when leaving the room.
8. Never throw rubbish on the floor.
9. Make sure you understand all instructions before using electrical equipment.
10. Always switch off or isolate before connecting or disconnecting any electrical equipment.
11. Take care when using flammable substances.
12. Know the location of fire extinguishers in the room and read the instructions of using it
carefully.
13. Have first aid treatment for every injury however trivial, contact immediately with the lab
instructor in case of any injury.
List of Experiments:

Exp. Name of the experiments

No.
1. a) Introduction to engineering drawing, its types, lettering system,
different types of lines and dimensioning.
b) Introduction to the instruments and their use in engineering drawing.
2. Orthographic drawing of objects with flat surface.
3. Orthographic drawing of objects with circular features.
4. Orthographic drawing of objects with circular holes.
5. Orthographic drawing of objects with slope.
6. Sectional Views.
7. Isometric drawing of objects.
8. Isometric drawing of objects with circular holes.
 Experiment No.: 01

Experiment Title:

a) Introduction to engineering drawing, its types, lettering system, different types of lines
and dimensioning.

b) Introduction to the instruments and their use in engineering drawing.

Theory

Introduction
Engineering drawing is a kind of drawing used by the engineers and technologists. It is the
communication medium between the various persons involved in the design and manufacture of
machines, building, bridges etc. For that matter it is often called graphic language. Mechanical
engineering drawing (mechanical drawing) is one class of engineering drawing that is used to
manufacture the various machine elements.

Drafting Instruments
The instruments which are used to perform the drawing are called drafting instruments such as,
drawing board, T-square, triangles, compasses, pencils etc. It may also be done with the help of a
computer.

T-Square: T-square is used to draw horizontal line. A T-square is shown in Figure 1.4. Usually a
student uses a T-square on a drawing board. The T-square is commonly made of wood with its
side made of transparent plastic. The head of the T-square is placed on the left edge of the board
for the right-handed person and vice versa. To draw the parallel lines by the T-square the head of
it has to be held firmly against the edge of the board.

T-Square
Triangles: They are used together with the straightedge of the T-square to draw the vertical and
the inclined lines.

45o and 30o- 60o Triangles

Drawing Lines with T-Square

Drawing a Horizontal Line

Drawing Lines with Triangles

Drawing a Vertical Line

Drawing Inclined Lines

Drawing Circle/Arc with Compass

Drawing Circles and Arcs

Types of Lines

Sl No. Types of Line Usage

1 Visible line / object line

to indicate all visible outlines of an object. It
shows the shape of an object.

2 Hidden line / dashed line

to represent the hidden edge of an object. It must
begin and end with a dash touching the visible
lines. Dashes that show hidden lines usually
touch each other at intersection.

3 Center line

to show the center line of holes, pitch line.

 4 Extension line, dimension line and
Leaders
to show dimension of an object extension line,
dimension line and leaders are used.

5 Section line

to indicate the cut portion of an object.

6 Cutting plane line to show the imaginary cutting of an object

7 ISO Cutting Plane Line to show the imaginary cutting of an object

8 Break line

to show a break on the object. It shortens the view

of a long part.

9 Phantom line/repeat line to show the alternate position of an object or the

position of an adjacent part.

Lettering
Lettering is an important part of drawing. For the description, figured dimension, notes on material,
finish, title etc. lettering is essential. Most of the lettering is done in single stroke either in vertical
or in inclined manner. However, only one style of lettering should be used throughout the drawing.
Lettering may be done either freehand or by templates. In the figure below, vertical gothic alphabet
has been shown. It is commonly used for all types of mechanical drawings. This type of letter is
easier to make and read. Each letter has been shown in a square to show the relative proportion of
the height and width of the letter. It can be observed that the heights and widths of the letters A,
O, Q, T, V, X, Y and Z are same. On the other hand, the widths of the letters M and W are more
than their heights. The heights of the rest letters are more than their widths. The heights of all the
numerals are more than their widths.

Vertical Gothic Alphabet

Arrowheads
The approximate length of the arrowhead may be 3 mm. However, for the larger drawing it may
be a little bit larger in size. The approximate ratio of the length to width of the arrowhead is 3:1 as
shown in the figure. The arrowhead must touch the line. It must not be either away from the line
or cross the line.

Arrowheads
Extension Line, Dimension Line and Leaders
Extension and dimension lines are used to show dimension of a part. Extension lines indicate the
point or line on the drawing to which the dimension is applied while dimension lines show the
dimensions. On the other hand, leaders are used to present note, dimension, symbol, item number
or part number on the drawings. They are thin lines.

Extension and Dimension Lines

Dimensioning of Angles

Dimensioning of Angles
Dimensioning in Circular Features

Dimensioning in Single Diameter

Dimensioning in Radii

Dimensioning in Cylindrical Holes

Through Hole Blind Hole

 Group of Holes

Task: 1. Prepare a drawing sheet according to the instruction given.

2. Write the vertical gothic alphabet.

3. Draw the given views with all the necessary dimensions.

 Experiment No.: 02

Experiment Title: Orthographic drawing of objects with flat surface.

Theory

Orthographic Projection
All objects have three dimensions such as length, breadth and height. The exact shape of an object
may be produced with the help of projection. Projection is the process in which the rays of sight
taken in a particular direction from an object to form an image on a plane called plane of projection
or picture plane. The image on the plane is called the view of the object.

(b)

(a)

(c)
Steps of orthographic projection
 Orthographic Projection

Task:
Draw the front, top and right-side views of the object given to you.
 Experiment No.: 03
Experiment Title: Orthographic drawing of objects with circular features.

Theory:

Curved features appear as a curved edge in one view, as a surface in the other two views.

Centerlines and Centermarks

Centerlines and centermarks are used to show the center of a circular or cylindrical feature.
Centerlines are drawn through the length of the center of a cylinder or circular hole and are shown
as alternating long and short dashes. Both centerlines and centermarks extend past the edges of the
circular feature.

Visible lines take precedence over all other lines, hidden lines take precedence over center lines,
center lines have lowest precedence.

Task:
Draw the front, top and right-side views of the object given to you.
 Experiment No.: 04

Experiment Title: Orthographic drawing of objects with circular holes.

Theory:

Read the theory of experiment 01, 02 and 03.

Circular or cylindrical holes appear as a circle in one view, and as hidden surfaces in other two
views.

Figure: Orthographic views of an object with holes.

Use of center marks and centerlines are discussed in experiment 03.

Dimensioning of cylindrical holes are discussed in experiment 01.

Task:
Draw the front, top and right-side views of the object given to you.
 Experiment No.: 05

Experiment Title: Orthographic drawing of objects with slope.

Theory:

Inclined surfaces are defined by the primary view to which they are perpendicular — in other
words, they are defined by the view in which they appear as an edge.

• An inclined frontal plane appears as an edge in the front view and as a surface in the top
and side.
• An inclined horizontal plane appears as an edge in the top view and as a surface in the front
and side.
• An inclined profile surface appears as an edge in the side view and as a surface in the front
and top.

Following figure illustrates the three classifications for inclined surfaces that are found on objects.

Figure: Inclined surface definitions

Task: Draw the front, top and right-side views of the object given.
 Experiment No.: 06

Experiment Title: Sectional Views.

Theory:

A sectional view is that view, which is seen beyond the imaginary cutting plane through an object
at right angle to the direction of sight. It represents the interior construction or details of hidden
features clearly to the users.

(a) (b)

Figure: (a) Object with Cutting Plane Through Mid-Section. (b) Section After Cutting and
Removal of Front Portion.

Figure: Views Showing Cutting Plane and Section

A cutting-plane line represents the plane, along which the object is cut. In Figure, the cutting plane
line has been shown on the view of the object, along which section has been made.

Section lining:

Section lining is often called cross-hatching. The purpose of section line is to indicate the surface
that has been cut hypothetically thereby clarifying the internal shape of the object and the material
from which the object is made of.

The lines used to indicate section are thin and they are usually drawn at an angle of 450 to the
major outline of the object. The spacing of the lines has to be reasonably uniform for good
appearance. The pitch or in other words the perpendicular distance between the consecutive lines
may vary between 1 to 3 mm.

Figure: Symbols for Section Lining

Task: Draw the sectional front view and top view of the object given.
 Experiment No.: 07

Experiment Title: Isometric drawing of objects.

Theory:

Making Isometric View

A simplified procedure is provided below to draw an isometric view from the orthographic
projection. In Figure1, the orthographic projection of an object is given from where an isometric
view will be drawn. The steps as mentioned below are to be followed to make the isometric view.

1. An isometric parallelepiped is drawn (Figure 2) in such a way that the length (l), breadth
(b) and height (h) of the parallelepiped are respectively equal to those of the orthographic
projection (Figure 1). The lines will be very thin so that they can be erased easily when
required.
2. Now the views are drawn on the respective side of the isometric parallelepiped keeping
appropriate relationship with each other (Figure 3). In drawing views the unnecessary lines
may be avoided otherwise, the drawing will be clumsy. The horizontal lines of the view
will be parallel to the isometric axes OB and OC while the vertical lines will be parallel to
the isometric axis OA. Each line will be thin.
3. Next shifting of the necessary surfaces is made keeping conformity with the views. Surface
a-b-c-d has been shifted to the new position a'-b'-c'-d' and surface p-q-r-s has been shifted
to the new position p'-q'-r'-s' (Figure 4).
4. The unnecessary lines are now erased, and the isometric view is completed making the
lines thick (Figure 5).
5. Finally, from the generated isometric view the orthographic projection may be verified to
confirm the drawing whether it has been done properly.
 Figure 1: Orthogonal Projection

Figure 2: Isometric Parallelepiped Figure 3: Views on Each Side

Figure 4: Shifting of Surfaces Figure 5: Isometric View

Task: Draw the isometric sketch of the objects from the given orthographic views.
 Experiment No.: 08

Experiment Title: Isometric drawing of objects with circular holes.

Theory:
Making Isometric View with Circular Features
A circle in the orthographic projection is transformed into the shape of an ellipse. In Figure 1 the
orthographic projection of an object with circular feature is provided. To make the isometric view
the steps as mentioned below are followed.
1. A square touching the circle is drawn with sides equal to the diameter of the circle on the
orthographic projection (Figure 2).
2. Now the isometric parallelepiped (Figure 3) is drawn as done earlier.
3. Next the views on the surfaces of the parallelepiped (Figure 4) are drawn with the square
of the circle omitting the circle itself. The square is turned into the shape of a rhombus.
The unnecessary lines may be avoided.
4. Now the lines on the rhombus are drawn as shown in Figure 5. Then the four centers c1,
c2, c3, and c4 are located.
5. The two arcs are drawn with radii c1b and c2a with respect to the centers c1 and c2
respectively. Next two other arcs are drawn with radii c3a and c4b with respect to the
centers c3 and c4 respectively (Figure 6).
6. Now the unnecessary lines are erased, and the isometric view is completed making the lines
thick (Figure 7).

Figure 1: Orthographic Projection

 Figure 2: Square Touching Circle

Figure 3: Isometric Parallelepiped Figure 4: Views on Faces of Parallelepiped

Figure 5: Location of Centers Figure 6: Drawing Arcs

Figure 7: Isometric Circle

Task: Draw the isometric sketch of the objects from the given orthographic views.
Drawing Sheet Samples:

Figure: Sample drawing sheet.

Figure: Title block dimensions.