Representing scale in engineering drawing

          The proportion between the drawing and the object can be represented by two ways as follows: 

a) Scale:- 1cm = 1m (or) 1cm = 100cm (or) 1:100

b) Representative Fraction:- (RF) = 1/100 

"The ratio of the length of the object represented on drawing to the actual length of the object represented is called the Representative Fraction (i.e., RF)".

There are three types of scales depending upon the proportion it indicates as 

1. Full Scale: Some times the actual dimensions of the object will be adopted on the drawing then in that case it is represented by the scale and RF as 

Scale:- 1cm = 1cm (or) 1:1 and by R.F =1/1 (equal to one)

2. Reducing scale: When the dimensions on the drawing are smaller than the actual dimensions of the object. It is represented by the scale and RF as 

Scale:- 1cm = 100cm (or) 1:100 and by R.F=1/100 (Less than one)

3. Enlarging scale: In some cases when the objects are very small like inside parts of a wrist watch, the dimensions adopted on the drawing will be bigger than the actual dimensions of the objects then in that case it is represented by scale and RF as 

Scale:- 10cm = 1cm (or) 10:1 and by R.F =10/1 (Greater than one)

Note: The scale or R.F of a drawing is given usually below the drawing. If the scale adopted is common for all figures under the title of the sheet.