Dr A Ramesh

1. SCALES
in
Engineering
Drawing

2. Scale:
The proportion by which the drawing of an
object is enlarged or reduced is called the
scale of the drawing.

3.  Reduction in dimensions creates ---------- a scale of that reduction ratio----- scale is called as Reducing Scale.
 Enlargement in dimensions creates------- a scale of that enlargement ratio--- scale is called as
Enlarging Scale.
 Ratio is called Representative Factor.
 Representative Fraction (RF) : It is the ratio of the dimension of the object shown on the drawing to its actual
dimension.
 There is a wide variation in sizes for engineering objects.
 It is not convenient, always, to draw drawings of the object to its actual size.
 Some are very large (e.g. Aero planes, rockets, Buildings, Heavy machines, Bridges etc.)
 Some are very small (wrist watch, MEMs (Micro - electromechanical Systems), Electronic
devices etc.
 There is a need to reduce or enlarge while drawing the objects on paper. Some objects can be drawn
to their actual size.

4. FOR EXPAMLE

5. Bureau of Indian Standards (BIS) Recommended Scales used for
general Engineering drawings

6. Types of Graphical Scale:
• Plain Scale
• Diagonal Scale
• Vernier Scale
• Comparative scale
• Scale of chords

8. • The R.F. of the scale.
• The unit which it must represent for example,millimters and
centimeters,or feet and inches etc.
• The maximum length which it must show.
• The length of the scale is determined by the formula:
length of the scale = ( R.F. )* (Maximum length required to
be measured)
To construct a scale the following information is essential

9. Plain Scale
• A plain scale consist of a line divided into
suitable no.of equal parts ,The first unit is
subdivided into smaller parts.
• It represent either two (or) a unit and its sub-
division.

10. • The zero should be placed at the end of the 1st main unit.
• From the zero mark, the units should be numbered to the right and the sub-
divisions to the left.
• Names of The units and the subdivisions should be labeled clearly
below or the respective ends.
• The R.F. should be mentioned below the scale.
In every scale,

11. Problem:
Construct a scale of 1:4 to show
decimeter and centimeters and long
enough to measure upto 5 decimeters.
Show the length of 3.7 dm on it.

12. Procedure:

13.  R.F.= 1/4
 Length of the scale = R.F. * Maximum length to be measured
= 1/4 * 5dm
= 1/4 * 5* 10cm
= 12.5cm
NOTE : 1decimeter = 10centimeter

14. DIAGONAL SCALE:
A Diagonal scale is used to represents three
units, i.e., main unit, its sub- unit and sub-units
of sub-units. Examples meters, decimeters and
centimeters.

15.  R.F.= 1/40
 Length of the scale = R.F. * Maximum length to be measured
= 1/40 * 6m
= 1/40 * 6* 100cm
= 15cm
NOTE : 1 meter = 100 centimeter
Construct a scale of 1:40 to read metres,decimeters and centimetres and
long enough to measure up to 6m.Mark a distance of 4.76m on it.