SCALES AND TYPES OF SCALES 

SCALES AND TYPES OF SCALES – Scale: All of us know that, always it is not possible to represent the actual size of an object on a drawing. So, it is required to reduce or increase the linear dimensions of the object, in order to accommodate it on a drawing, in some proportion. The ratio by which the original length of the object is decrease or Increased is known as the ‘Scale.

Full Size Scale: If the actual size of the object is shown on the drawing, the scale used is said to be a full size scale. Representative Fraction (RF)=1:1

Reduced Scale: If the actual size of the object is reduced in order to accommodate it on the drawing sheet the scale used is said to be a reduced scale. Ex: Plan of a building.Representative Fraction (RF)=1:100

Enlarged Scale: If the actual size of an object is enlarged, to show then details more clearly on the drawing, the scale used is said to be an enlarged scale. Ex: Machine spare part.Representative Fraction (RF)=10:1

Types of Scales:

Scales may be classified as follows:

1. Plain
2. Diagonal scale
3. Vernier scale
4. Scale of chords

The surveyor should have good knowledge of the plain and diagonal scales
•Plain Scale: A plain scale is one on which it is possible to measure two dimensions only, such as units of lengths. “km, m,and decimeters” etc.
•Diagonal Scale: This is a scale used to represent three successive units, tenth and hundredths; such as kilometers, hectometers. decameters, yards, feets and inches etc.
•Length of Scale: The length of scale should be calculated according to the maximum length to shown, when maximum. Length is not given, the length of scale may be taken 10 to 15 cm.

Representative Fraction (RF): The ratio of map distance to the corresponding ground distance is independent of units of measurements and this ratio is called representative fraction.

RF = distance on map/ corresponding actual distance on ground
For example,
If a scale is 1 cm = 20 m, then
RF=1/20×100
=1 /2000 or 1:2000