�ݺ�ߣ

ENGINEERING GRAPHICS
SCALES
• Introduction
• Representative Fraction
• Types of Scales

INTRODUCTION
 Usually the word scale is used for an instrument
used for drawing straight lines.
 But actually in Engineer’s language scale means
the proportion or ratio between the dimensions
adopted for the drawing and the corresponding
dimensions of the object.

INTRODUCTION
 I.S. have recommended the following standard
scales.
 Full Scale (1:1)
 Reduced Scale
1 : 2 1 : 2.5 1 : 5
1 : 10 1 : 20 1 : 50
1 : 100 1 : 200
 Enlarged Scale
10 : 1 5 : 1 2 : 1

REPRESENTATIVE FRACTION (R.F.)
 The ratio of the size of the element in the drawing
to the size of the same element in the object is
called the Representative Fraction (R.F.).

Example 1
 If 1 cm length of drawing represents 5 m length of
the object, then in engineering scale it is written as
1 cm = 5 m and in graphical scale it is denoted by

Example 2
 If a 5 cm long line in the drawing represents 3 km
length of a road, then in engineering scale it is
written as 1 cm = 600 m and in graphical scale it is
denoted by

Example 3
 If a gear with a 15 cm diameter in the drawing
represents an actual gear of 6 mm diameter in
graphical scale, it is expressed by

TYPES OF SCALES
1.
 Mechanical Engineers’
scale
 Architects’ scale
 Civil Engineers’ scale
2.
 Plain scale
 Diagonal scale
 Comparative scale
 Vernier scale
 Scale of Chords
 Isometric scale
Scales are classified in two different manner as under:

TYPES OF SCALES
 These scales are 300
mm long and each unit
is sub-divided.
 Mechanical Engineers
generally use following
scales.
1:1 1:2 1:2.5 1:5
2:1 5:1
Mechanical Engineers’ scale

TYPES OF SCALES
 Architects are required
to take very small R.F.
since buildings are
comparatively very big
as compared to
drawing paper size.
 Only the first main
division of the
architects’ scale is sub-
divided.
Architects’ scale

TYPES OF SCALES
 Civil Engineers dealing
with road maps and
survey maps are
required to take very
very small R.F..
 These scales are sub-
divided on their entire
lengths.
Civil Engineers’ scale

PLAIN SCALES
 Plain scales read or measure upto two units or a unit and its
sub-division, for example centimeters (cm) and millimeters
(mm).
 When measurements are required upto first decimal, for
example 2.3 m or 4.6 cm etc.
 It consists of a line divided into number of equal main parts
and the first main part is sub-divided into smaller parts.

PLAIN SCALES
Example
 A 3 cm long line represents a length of 4.5 meters.
Extend this line to measure upto 30 meters and
show on it units of meter and 5 meter. Show the
length of 22 meters on this line.

Construction:
 Draw a straight line of 20cm length and divide into 6 equal parts.
 Divide again first part into 5 equal parts. Give numbers as shown. To
represent 22 meters, take 4 main parts to represent 20 meters and 2
small parts to represent 2meters. Give names as A and B so that the
distance between A and B is 22 meters as shown.
 Note: Assume height of the plain scale as 1 cm.

DIAGONAL SCALES
 Diagonal scales are used to read or measure upto three units.
 For example: decimeters (dm), centimeters (cm) and millimeters (mm) or
miles, furlongs and yards etc. This scale is used when very small
distances such as 0.1 mm are to be accurately measured or when
measurements are required upto second decimal.
 For example: 2.35dm or 4.68km etc.
 Small divisions of short lines are obtained by the principle of diagonal
division, as explained below:
 Principle of diagonal scale: To divide a given line AB into small divisions
in multiples of 1/10 its length for example 0.1AB; 0.2AB etc.

DIAGONAL SCALES
Example
 An area of 144 sq. cm on a map represents an area
of 9 sq. km on the field. Find the R.F. of the scale
for this map and draw a diagonal scale to show
kilometers, hectometers and decameters and to
measure upto 5 kilometers. Indicate on the scale a
distance of 3 kilometers, 5 hectometers and 6
decameters or 3.56km.

Construction:
 Draw a line AB of 20 cm and construct a rectangle on it, by taking AD
5cm as shown. Divide AB into 5 equal parts and number them from
second part starting with 0 to 4 towards right side to indicate kilometers
(km). Divide 0A into 10 equal parts, each part represents a hectometer
(hm). Divide AD into 10 equal parts, each part represents one decameter
(dam). Join diagonals as shown.
 To mark 3.56km, take it as sum of 3.50km and 0.06km. On the plain
scale take 3.5km and on the diagonal at 5 upto 6 parts diagonally which
is equal to 0.06km, giving a total of 3.56km as shown by MN.
 Note: Assume the height of the diagonal scale AD as 5cm for dividing it
into 10 equal parts conveniently.

ISOMETRIC SCALES
 A scale is now constructed by stepping
off true measurements along line 'AB1'
which is a true length line.
 The measurements are then transferred
back to line 'AB' to get a smaller scale, in
this case an isometric scale.
 Lines drawn using the isometric scale
are approximately 80% of true size. This
scale is usually marked off on a piece of
paper and used to step off the
foreshortened measurements along the
projection of axes lines and lines parallel
to them.
 Lines parallel to the projection of axes
are known as isometric lines.
 Lines which are not parallel to theses
axes are known as non-isometric lines.
 It is important to note that you can only
use the scales on isometric lines.

�ݺ�ߣ

Scales

More Related Content

Scales

Editor's Notes