Engineering graphics introduction converted

Dr.R. GANESAMOORTHY.B.E.,M.E.,Ph.d.
Professor –Mechanical Engineering
Saveetha Engineering College
Tandalam
Chennai.
24-Sep-18 1Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS

Definition
Engineering graphics is the language for
Effective Communication among engineers which
elaborates the details of any component,
structure or circuit at its initial drawing through
drawing.

DRAFTING TOOLS
❖ Drawing Board
❖ Mini drafter or T- square
❖ Drawing Instrument box
❖ Drawing Pencils
❖ Eraser
❖ Templates
❖ Set squares
❖ Protractor
❖Scale Set
❖French curves
❖Drawing clips
❖Duster piece of cloth(or)
brush
❖Sand-paper (or) Emery
sheet block
❖Drawing sheet
The following are the various drafting tools used in
engineering graphics.

DRAFTING TOOLS
24-Sep-18 Dr.RGM PROF/MECH / UNIT 1 ENGG GRAPHICS 4

Drawing Sheet
Designatio
n
Dimension, mm
A0 841 x 1189
A1 594 x 841
A2 420 x 594
A3 297 x 420
A4 210 x 297

Lines
• Visible Outlines, Visible ,Edges- Continuous wide lines
• Dimension Lines - Continuous narrow Lines
• Extension Lines - Continuous narrow Lines
• Construction Lines - Continuous narrow Lines
• Hatching / Section Lines - Continuous narrow Lines
• Guide Lines - Continuous narrow Lines
• Break Lines - Continuous Narrow Freehand Lines
• Break Lines - Continuous Narrow Lines With Zigzags
• Dashed Narrow Lines - Dashed Narrow Lines
• Centre Lines - Long-Dashed Dotted Narrow Lines
• Cutting Plane Lines - long-dashed dotted narrow line
• Border Lines - Continuous wide lines

Types of Lines and their applications
1.Continuous narrow line-Dimension lines, Extension
lines, Leader lines, Reference lines, Short centre lines,
Projection lines, Hatching, Construction lines, Guide lines,
Outlines of revolved sections ,Imaginary lines of
intersection
2.Continuous narrow freehand line-Preferably manually
represented termination of partial or interrupted views,
Cuts and sections, if the limit is not a line of symmetry or
a Centre line·

Conti........
3.Continuous narrow line with zigzags -Preferably
mechanically represented termination of partial or
interrupted views. cuts and sections, if the limit is not a
line of symmetry or a centre line .
4.Continuous wide line -Visible edges, visible outlines,
Main representations in diagrams, maps. flow charts.
5.Dashed narrow line -Hidden edges ,Hidden outlines

Conti........
6.Long-dashed dotted narrow line -Centre lines /
Axes. Lines of symmetry, Cutting planes
7. Long-dashed dotted wide line-Cutting planes at
the ends and changes of direction outlines of visible
parts situated front of cutting plane

Dimensioning
Dimensioning provided through the distances between
the surfaces, location of holes, nature of surface finish,
type of material, etc.
Elements of dimensioning
1.Dimension line
2.Leader line
3.Origin indication
4.Dimension
5.Projection or extension line
6. Dimension line termination

Principles of Dimensioning
I. All dimensional information necessary to describe a
component clearly and completely shall be written
directly on a drawing.
2. Each feature shall be dimensioned once only on a
drawing, i.e., dimension marked in one view need
not be repeated in another view.

Conti.....
3. Dimension should be placed on the view where the
shape is best seen (Fig.)
4. As far as possible, dimensions should be expressed
in one unit only preferably in millimetres, without
showing the unit symbol (mm).

Conti.....
5. As far as possible dimensions should be placed
outside the view (Fig.).
6. Dimensions should be taken from visible outlines
rather than from hidden lines (Fig.)

Conti.....
7. No gap should be left between the feature and the
start of the extension line(Fig.).
8. Crossing of centre lines should be done by a long
dash and not a short dash (Fig.).

Methods of Indicating Dimensions
Method - 1 (Aligned method).
Method - 2 (Uni -directional method)

Arrangement of Dimensions
They are arranged in three ways.
1. Chain dimensioning 2. Parallel dimensioning
3. Combined dimensioning.

Set of Scales
Scales are used to make drawing of the objects to
proportionate size desired. These are made of wood,
steel or plastic.
M1 M2 M3 M4 M5 M6 M7 M8
Scale on one
edge
1:1 1:25 1:10 1:50 1:200 1:300 1:400 1:1000
Scale on other
edge
1:2 1:5 1:20 1:100 1:500 1:600 1:800 1:2000Scales for use on technical drawings(IS: 46-
1988)
Category Category Recommended scales
Enlargeme
nt scales
50 : 1
5 : 1
20 : 1
2 : 1
10 : 1
Full size 1 : 1
Reduction
scales
1 : 2
1 : 20
1 : 200
1 : 2000
1 : 5
1 : 50
1 : 500
1 : 5000
1 : 10
1 : 100
1 : 1000
1 : 10000

Scale
Definition :
Scale is defined as the ratio of the linear dimension of
an element of an object as represented in the original
drawing to the linear dimension of the same element of
the object itself.
Full size scale
If we show the actual length of an object on a drawing,
then the scale used is called full size scale.

Scale Conti…..
Reducing scale
If we reduce the actual length of an object so as to
accommodate that object on drawing, then scale used is
called reducing scale.
Enlarging scale
Drawings of smaller machine parts, mechanical instruments,
watches, etc. are made larger than their real size. These are
said to be drawn in an increasing or enlarging scale.

Representative Fraction (R.F)
The ratio of the drawing of an object to its actual size is
Called the representative fraction, usually referred to as
R.F.
R.F=Drawing of an object/It’s actual size(in same units)
For reducing scale, the drawings will have R.F. values of
Less than unity.
if 1 cm on drawing represents
1 m length of an object.

Representative Fraction (R.F) conti....
Increasing or enlarging scale, the R.F values will be
Greater than unity.
For example, when 1 mm length of an object is shown by
a length of 1cm on the drawing

Types of Scales
Types of Scales
1.Simple scales
2. Diagonal scales
3. Vernier scales
Simple scales
A plain scale is simply a line, which is divided into a
suitable number of equal parts, the first of which is further
sub-divided into small parts.
It is used to represent either two units or a unit and its
fraction such as km, m and dm, etc.

Types of Scales Conti.....
Plain scales , Diagonal Scales, Vernier Scale
Plain scales are used to read lengths in two units such as
metres and decimetres or to read the accuracy correct to
first decimal.
Diagonal scales are used to represent either three units
of measurements such as metres, decimetres, centimetres
or to read to the accuracy correct to two decimals.
The diagonal scales, vernier scales are used to read very
Small units with accuracy.
They are used, when a diagonal Scale is inconvenient to
use due to lack of space.

Vernier scale
A vernier Scale consists of two parts, i.e., Main scale
and a vernier.
The main scale is a Plain scale divided into minor
divisions.
The vernier is also a scale used along with the main
scale to read the third unit, which is the fraction of
the second unit on the main scale.

Least count: Least count the smallest distance
that can be measured accurately by the vernier
scale and is the vernier scale and is the difference
between a main scale division and a vernier scale
division.
Types of Verniers:
1. Forward vernier or direct vernier
2. Backward vernier or retrograde vernier

Lettering
Technical lettering is the process of forming letters,
numerals, and other characters in technical drawing. It is
used to describe, or provide detailed specifications for, an
object.
Characteristic Parameter Ratio Dimensions(mm)
Lettering Height
(Height of capitals)
h (14/14)h 2.5 3.5 5 7 10 14 20
Height of lower case
letters
(without stem or tail)
c (10/14)h - 2.5 3.5 5 7 10 14
Spacing between
characters
a (2/14)h 0.35 0.5 0.7 1 1.4 2 2.8
Minimum spacing of base
characters
b (20/14)h 3.5 5 7 10 14 20 28
Minimum spacing
between words
e (6/14)h 1.05 1.5 2.1 3 4.2 6 8.4

Lettering Conti.....
Characteristic Parameter Ratio Dimensions(mm)
Lettering Height
(Height of capitals)
h (10/10)h 2.5 3.5 5 7 10 14 20
Height of lower case letters
(without stem or tail)
c (7/10)h - 2.5 3.5 5 7 10 14
Spacing between
characters
a (2/10)h 0.5 0.7 1 1.4 2 2.8 4
Minimum spacing of base
characters
b (14/10)h 3.5 5 7 10 14 20 28
Minimum spacing between
words
e (6/10)h 1.5 2.1 3 4.2 6 8.4 12
Thickness of lines d (1/10)h 0.25 0.35 0.5 0.7 1 1.4 2

Geometric Construction
Drawing consists of construction of primitive geometric
forms viz. points, lines and planes that serve at building
blocks . The use of lines for obtaining the drawing of
planes

Geometric Construction Conti........
Solids are obtained by combination of planes. Plane
surfaces of simple solids are shown in figure.

To divide a straight line into a given
number of equal parts say 5. Construction
1. Draw AC at any angle θ to AB.
2. Construct the required number of equal parts of
convenient length on AC like 1,2,3.
3. Join the last point 5 to B
4. Through 4, 3, 2, 1 draw lines parallel to 5B to intersect
AB at 4',3',2' and 1'.

1. Draw a line AB and AC making the given angle.
2. With centre A and any convenient radius R draw an
arc intersecting the sides at D and E.
3. With centers D and E and radius larger than half the
chord length DE, draw arcs intersecting at F
4. Join AF, <BAF = <PAC.
To bisect a given angle Construction

To inscribe a square in a given
circle Construction
1. With centre 0, draw a circle of diameter D.
2. Through the centre 0, draw two diameters, say AC and
BD at right angle to each other.
3. Join A-B, B-C, C- D, and D-A. ABCD is the required
square.

To inscribe a hexagon in a given
circle.
By using a set-square or mini-draughter
1. With centre 0 and radius R draw the given circle.
2. Draw any diameter AD to the circle.
3. Using 30° - 60° set-square and through the point A draw lines AI, A2 at an
angle 60° with AD, intersecting the circle at B and F respectively.
4. Using 30° - 60° and through the point D draw lines Dl, D2 at an angle 60° with
DA, intersecting the circle at C and E respectively.
By joining A, B, C, D, E, F, and A the required hexagon is obtained.

To inscribe a hexagon in a given
circle.
By using compass
2. Draw any diameter AD to the circle.
3. With centres A and D and radius equal to the radius of the circle draw
arcs intersecting the circles at B, F, C and E respectively.
4. ABC D E F is the required hexagon.

To circumscribe a hexagon on a given
circle of radius R construction
2. Using 60° position of the mini draughter or 300-
600set square, circumscribe the hexagon as shown.

To construct a hexagon, given the
length of the side
(a)Using set square
1. Draw a line AB equal to the side of the hexagon.
2. Using 30° - 60° set-square draw lines AI, A2, and BI,B2.
3. Through 0, the point of intersection between the lines
A2 at D and B2 at E.
4. Join D,E
5. ABC D E F is the required hexagon.

To construct a hexagon, given the
length of the side
(b) By using compass
1. Draw a line AB equal to the of side of the hexagon.
2. with centres A and B and radius AB, draw arcs
intersecting at 0, the centre of the hexagon.
3. With centres 0 and B and radius OB (=AB) draw arcs
intersecting at C.
4. Obtain points D, E and F in a similar manner.

To construct a regular polygon
(say a pentagon) given the length
of the side.
1. Draw a line AB equal to the side and extend to P such that AB = BP
2. Draw a semicircle on AP and divide it into 5 equal parts by trial and error.
3. Join B to second division
4. Irrespective of the number of sides of the polygon B is always joined to
the second division.
5. Draw the perpendicular bisectors of AB and B2 to intersect at O.
6. Draw a circle with 0 as centre and OB as radius.
7. With AB as radius intersect the circle
successively at D and E.Then join CD.
DE and EA.

To construct a regular polygon
(say a hexagon) given the side AB
– alternate Method.
1. Steps 1 to 3 are same as above
2. Join B- 3, B-4, B-5 and produce them.
3. With 2 as centre and radius AB intersect the line B, 3
produced at D. Similarly get the point E and F.
4. Join 2- D, D-E, E-F and F-A
to get the required hexagon.

To construct a pentagon, given
the length of side.
1. Draw a line AB equal to the given length of side.
2. Bisect AB at P.
3. Draw a line BQ equal to AB in length and perpendicular to AB.
4. With centre P and radius PQ, draw an arc intersecting AB produced at R.
AR is equal to the diagonal length of the pentagon.
5. With centres A and B and radii AR and AB respectively draw arcs
intersecting at C.
6. With centres A and B and radius AR draw arcs
intersecting at D.
7. With centres A and B and radii AB and AR
respectively draw arcs intersecting at E.
ABCDE is the required pentagon.

By included angle method
1.Draw a line AB equal to the length of the given side.
2.Draw a line B 1 such that <AB 1 = 108° (included angle)
3.Mark C on B1 such that BC = AB
4.Repeat steps 2 and 3 and complete the pentagon ABCDE
To construct a pentagon, given the
length of side.

Engineering graphics introduction converted

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