This document provides an overview of technical drawing, including: 1. It defines technical drawing as a communication method that uses lines, symbols, dimensions, and notations to accurately describe objects. 2. It distinguishes technical drawing from artistic drawing, noting that technical drawing is used to convey precise design information while artistic drawing expresses ideas. 3. It discusses the different types of technical drawings like instrument drawings, computer-aided drawings, sketches, details drawings, assembly drawings, and pictorial drawings.

1. 1

2. Definition of Technical
Drawing
 Drawing is distinctively classified into
two major classes known as:
1. Artistic drawing
2. Technical drawing
Artistic drawings are used to express
aesthetic ideas, philosophic
imaginations, and abstract ideas.
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3. Cont...
 Technical drawing is a universal
communication media through which
ideas and thoughts are conveyed from one
person to another.
 Technical drawing 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.
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4.  When drawings are made with the use of
instruments, they are called instrument(or
board) drawing.
 When they are developed using computer
they are known as computer-aided
drawings.
 When made without instruments or the aid
of computer, drawings are referred to as
sketches.
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5. Cont….
 Mechanical drawing for Engineers
◦ Advantage
 It is technical
 Exact
 Clearest way to communicate
 It is a universal language
◦ Disadvantage
 Time consuming to produce
 It needs skill
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6. Cont…
 Sketches
◦ describe the concept in general
 Layout
◦ show the relationships of parts and defines key
dimensions
 Details
 Assembly
 Pictorial
◦ for technical manuals, sales literature, or Internet
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7. Drawing representation
 Detail drawing
◦ Drawings of single parts
◦ May be drawn one part per sheet
◦ May be several parts detailed on a large
sheet
◦ Include info such as dimensions and
notes relating to material, finish, weight, or
tolerance
◦ includes all of the information needed to
fabricate the part.
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8. Cont…
 Assembly Drawings
◦ Show how parts fit together or are
functionally related
◦ Dimensions typically refer to relationships
among the parts
◦ Often a bill of materials (listing of all parts
necessary to make up the total assembly)
is included.
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9. Care and use of drawing instrument and
materials
 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.
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10. Cont…
 List of drawing instruments
◦ Drawing board
◦ Drawing sheets
◦ T-square, or parallel-ruling straightedge, or
drafting machine
◦ Drafting tape
◦ Drafting pencils
◦ Pencil sharpener
◦ Lettering instrument
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11. Cont…
◦ Eraser
◦ Erasing shield
◦ Triangle (Set-square) (450 and 300 - 600)
◦ Architect’s or engineer’s scale
◦ Irregular curves (French curve)
◦ Drawing instrument set (Compass, Divider,
extensions)
◦ Protractor
◦ Templates
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12. Scales
There is a wide variation in sizes for engineering objects. Some are
very large, Some are vey small ( wrist watch, MEMs components)
There is a need to reduce or enlarge while drawing the objects on paper.
Some objects can be drawn to their actual size. The proportion by
which the drawing of an object is enlarged or reduced is called the scale
of the drawing.
Definition
A scale is defined as the ratio of the linear dimensions of the object
as represented in a drawing to the actual dimensions of the same.
Drawings drawn with the same size as the objects are called full sized
drawing.
Generally scales are used to prepare drawing at
Full size
Reduced size
Enlarged size 10/22/2019 Eng. Drawing 12

13. n
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14.  Definition:
- Line is the most basic design 'tool'.
- A line has length, width, tone, and texture.
- It may divide space, define a form, describe
contour, suggest direction.
Examples:
"A line is a dot that went for a walk." - Paul Klee.
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15. 1. Visible Lines: Dark, heavy lines with approximate width 0.6mm.
Show the outline and shape of an object.
Define features you can see in a particular view.
2. Hidden Lines: Light/medium, narrow, short dashed lines with
approximate width 0.3mm.
Shows the outline of a feature that can not be seen in a particular
view.
Used to help clarify a feature, but can be omitted if they clutter a
drawing.
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16. 3. Section Lines: Thin lines usually drawn at a 45 degree angle.
Indicate the material that has been cut through in a sectional view.
Section Line
4. Center Lines: Thin line consisting of long and short dashes.
Shows the center of holes, slots, paths of rotation, and symmetrical
objects.
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17. 5. Dimension Lines: Thin, dark lines.
Show the length, width, and height of the features of an object.
Terminated with arrowheads at the end.
6. Extension Lines: Thin line used to show the starting and
stopping points of a dimension.
Must have at least a 1mm space between the object and the
extension line.
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Dimension
Line
Extension
Line

18. 7. Leader Lines: Thin lines.
Used to show the dimension of a feature or a note that is too large to
be placed beside the feature itself.
8. Cutting Plane Lines: Thick broken line that is terminated with short
90 degree arrowheads.
Shows where a part is mentally cut in half to better see the interior
detail.
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Leader Line

19. 9. Break Lines: Used to break out sections for clarity or for
shortening a part.
Three types of break lines with different line weights.
a. Short Breaks. Thick wavy line.
Used to break the edge or surface of a part for clarity of a hidden
surface.
b. Long Breaks. Long, thin lines.
Used to show that the middle section of an object has been removed so
it can be drawn on a smaller piece of paper.
c. Cylindrical Breaks. Thin lines.
Used to show round parts that are broken in half to better clarify the
print or to reduce the length of the object.
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20. 10. Phantom Lines: Thin lines made up of long dashes alternating
with pairs of short dashes.
Three purposes in drawings.
1.To show the alternate position of
moving parts.
2. To show the relationship of parts
that fit together.
3.To show repeated detail.
Phantom lines can show where a part is
moving to and from.
Eliminates the confusion of thinking there may be 2 parts instead of just
1.
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Phantom Lines

21. Drawing consists of construction of primitive geometric
forms viz. points, lines and planes that serve as the
building blocks for more complicated geometric shapes
and defining the position of object in space.
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22. Cont….
The use of lines for obtaining the drawing of planes is shown in figure 1 below.
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23. Solids are obtained by combination of planes. Plane surfaces
of simple solids are shown in figure 2.
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24. Point
A point is a theoretical location that has neither width, height, nor
depth and describes exact location in space. A point is represented
in technical drawing as a small cross made of dashes that are
approximately 3 mm long. As shown in figure 4, a point is used to
mark the locations of centers and loci, the intersection ends, middle
of entities.
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25. A line is a geometric primitive that has length and direction, but
no thickness. Lines may be straight, curved or a combination of
these. As shown in figure 5, lines have few important relationship
or conditions, such as parallel, intersecting, and tangent. Lines
can be of specific length or non-specific length. A Ray is a
Straight line that extends to infinity from a specified point.
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26. Bisecting a line
The procedure of bisecting a given line AB is illustrated in figure 6.
With A as centre and radius equal to higher than half AB, draw two
arcs. With B as centre and with the same radius draw another arc
intersecting the preious arcs. The line joining the intersection points
is the perpendicular bisector of the line AB.
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27. Locating tangent points on circle and arcs
The method of locating tangent points on circle and arcs as well as
the common tangent to two circles are shown in figure 9(a) and (b) .
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28. Drawing an arc tangent to a given point on the line
The steps for drawing the arc tangent to a given point on a line is
shown in figure 10.
Given line AB and tangent point T. Construct a line perpendicular
to line AB and through point T.
Locate the center of the arc
by making the radius on the
perpendicular line. Put the
point of the compass at the
center of the arc, set the compass
for the radius of the arc,
and draw the arc which will be
tangent to the line through
the point T.
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29. Drawing an arc, tangent to two lines
The steps used to drawn an arc tangent to two lines is illustrated in
figure 11.
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30. Drawing an arc, tangent to a line and an arc
Figure 12 shows the steps in drawing an arc tangent to a line and
an arc that (a) that do not intersect and (b) that intersect each
other.
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31. Construction of Regular Polygon of given length AB
To construct a regular polygon with length of edge AB us shown in
figure 1
Draw a line of length AB. With A as centre and radius AB, draw a
semicircle.
With the divider, divide the semicircle into the number of
sides (example of number of side 7 is shown in figure 1) of the
polygon.
Draw a line joining A with the second division-point 2.
The perpendicular bisectors of A2 and AB meet at O. Draw a
circle with centre O and radius OA.
With length A2, mark points F, E, D & C on the circumferences
starting from 2 (Inscribe circle method)
With centre B and radius AB draw an arc cutting the line A6
produced at C. Repeat this for other points D, E & F (Arc method)
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32. Cont….
Fig.1 Construction of a regular polygon with a given length of edge.
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33. Borders and Title Blocks
 Borders
◦ provides a safety area to prevent the loss of
important information
◦ approve appearance for presentation purposes
 Title Blocks
◦ some items standard: drawing number, sheet
number, title, company name, logo, scale,
date, tolerances, drafter, checker, supervisor
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34. Laying out of the paper
 Before start drawing, prepare drawing
instruments and clean them properly
 The drawing table is to be set in the way
of light comes from the left
 Attach the paper near the left edge or
position at equal distance in all directions
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35. Cont…
How to begin your drawing?
To start with the preparation of a drawing the procedure
mentioned below may be followed:
Clean the drawing board and all the drawing instruments using
duster.
Fix the drawing sheet on the drawing board.
Fix the mini-drafter in a convenient position.
Draw border lines using HB pencil..
Complete the title box using HB pencil .
Plan spacing of drawings b/n two problems/views beforehand.
Print the problem number on the left top and then commence
the drawing work.
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36. Cont….
Keeping the drawing clean is a must
Never sharpen pencils over drawing.
Clean pencil point with a soft cloth after sharpening.
Keep drawing instruments clean.
Rest hands on drawing instruments as much as possible – to
avoid smearing the graphite on the drawing.
When darkening lines – try to work from the top of the drawing
to the bottom, and from left to the right across the drawing.
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37. Lettering techniques
 An H or F are grade pencils are generally
preferred.
 Keep the pencil sharp: rotate it in your finger
every letter or two.
 Hold the pencil in comfortable relaxed
manner: don’t grip to tight
 Place your arm and body in comfortable
position
 Disk containing letters of the alphabets are
also available
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38. Recommended lettering
 Inclined lettering is drawn at 68˚
 Small letters are as wide as they are high
 Capitals J, D, R, F, N, C, G, U, P, B, L, E
and H are 5/6 as wide as they high
 Capitals O, Q, S, T, A, K, V, M, X, Y and
& are as wide as they are high
 W is wider than it is high
 I is exceptional
 Numerals are 5/6 as wide as they are high.
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39. Cont...
 Letters B, E, F, & H are drawn with horizontal
element slightly above the center
 Letters K, S, X, Z, 2, 3 & 8 are drawn with
width of the top half smaller than the bottom
half for good stability.
 Examine the stability of 4, 5, 6, and 9
 The height of letters recommended for Titles
may range from 6mm to 8mm
 Notes and dimensions may be lettered 3mm
and fractional numbers may be about 6mm
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40. Guide lines
 Lettering should never done without guide lines.
 Guide lines are very light
 Horizontal guide lines to regulate the height of
letters
 Vertical and sloping to keep the letters uniformly
vertical and inclined
 Capital lettering(Cap line and base lines)
 Small letters(Cap line, waist line, base line and
drop line)
 Five equally spaced light lines are used for
fractional numbers
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41. Word Composition
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Space between the letters depends on the contour of
the letters at an adjacent side.
Good spacing creates approximately equal background
area between letters.

42. Neatness of a drawing
 Should be complete and unambiguous
 Should be neat and easy to read
 Use only as many views as necessary to
show all required detail
 Apply tolerances realistically - overly
tight tolerances can add a great deal of
additional cost with little or not added
value to the part
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43. Thank you!
The end
( Chapter1 Part One)
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