The document outlines the concepts of scales used in engineering drawings, specifically full size, reduced, and enlarged scales with respective ratios. It details the representative fraction (r.f.) and classifications of scales, including plain and diagonal scales, alongside instructions for constructing a plain scale. Additionally, it provides examples and assignments related to constructing scales with specific requirements.

1. WELCOME
SVPM’s INSTITUTE OF TECHNOLOGY AND ENGINEERING,
MALEGAON (Bk)
2020-21

2. Lecturer:- Mr. Kadam S.P.
(M.E. CDA/CAM)
SVPM’S Institute of Technology and Engineering,
Malegaon(Bk)
Automobile Engineering Department

3. Scales – Reduced, Enlarged and Full Size
Some objects like building machines etc. are big, some
objects are very small (e.g. parts used in wrist
watches). Their drawing is required to be drawn
proportionally reduced or enlarged. The proportion by
which we are enlarging or reducing actual length of
object on drawing is known as scale.

4. Scale size: Following scale sizes used in engineering practice
1. Full size scale: The scale in which objects are drawn with actual
measurements is known as full size scale. It is written as 1:1.
2. Reduced scale: The scale in which objects are drawn with reduced
proportion is known as reduced scale. Standard reducing proportions
are :
1:2 – drawing made to one half of the actual size.
1:10 – drawing made to one tenth of the actual size.
3. Enlarged Scale: The scale in which objects are drawn with enlarged
proportion is known as enlarged scale. Standard enlarged proportions
are :
2:1 – drawing made to twice the actual size.
10:1 – drawing made to ten times the actual size.

5. Representative Fraction (R.F)
 It is the ratio of the length of object on the drawing to the actual length of
object
 For enlarging scale R.F. is more than one. It is less than one for reducing
scale. When 1cm long line in drawing represents 10 cm length of the object
= and the scale of drawing will beof full size
and represented as 1:10
𝑅. 𝐹 .=
h
𝐿𝑒𝑛𝑔𝑡 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡𝑜𝑛 h
𝑡 𝑒 𝑑𝑟𝑎𝑤𝑖𝑛𝑔
𝐴𝑐𝑡𝑢𝑎𝑙 h
𝑙𝑒𝑛𝑔𝑡 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡

6. of meter
of meter
of meter
meter
meter
meter

7. Types of scales:
The scales are classified as
1. Simple or plain scale
2. Diagonal scale
Plain Scale
Plain scales are used to read length in two units such as meters and
decimeters or to read the accuracy correct to first decimals.

8. Steps in constructing the scales:
1. Calculate the length of scale, using the relation,
Length of scale = R.F. X Length to be measured
2. Draw two lines parallel to each other and some distance apart so that they give
appearance as rule. Join the ends by vertical lines.
3. Divide the line into required number of equal parts.
4. Draw the perpendicular lines at these division points.
5. Mark ‘zero’ at the end of first division.
6. Subdivide only first main part to the left of zero into the required number of
subdivisions.
7. The subdivisions are numbered to the left, starting from zero.
8. The main units are numbered to the right, starting from zero.
9. Units of measurement of the main unit and its sub divisions are to be indicated.
10. Name of the scale and R.F. should be mentioned below the scale.

9. 1. Construct plain scale with R.F. 1:40 to read up to 5 meters in meters and decimeters
1. Calculate the length of scale which is given by
Length of scale = R.F. X Length to be measured
= X 5 = 0.125m i.e. 125mm
2. Draw two parallel lines 125mm long and some distance apart so that they give appearance as
rule. Join the ends by vertical lines.
3. Divide into five equal parts , each showing meter.
4. Draw perpendicular lines at these meter divisions, 0, 1, 2, 3 and 4
5. Divide first part from left into 10 equal parts, each showing decimeter.
6. At each decimeter division, raise perpendicular and name every second decimeter of the scale
as shown.
The reading of 3 meters and 2 decimeters i.e. 3.2. m is shown on the scale.

10. Assignments on Plain Scale:
1. Construct plain scale with R.F. 1:400 to read up to 60 meters and mark on it distance of
43 meters.
2. Construct plain scale with R.F. 1:8 to show feet and inches and long enough to measure
up to 4 feet. Show distance of 2 feet and 7 inches on your scale