Engineering Graphics '' SCALE ''

Dimensions of large objects must be reduced to accommodate on standard size drawing sheet. This reduction creates a SCALE of that reduction scale, which is generally a fraction. Such a scale is called REDUCING SCALE.
AND that ratio is called REPRESENTATIVE FACTOR.

USE FOLLOWING FORMULAS FOR THE CALCULATIONS IN THIS TOPIC.



>> REPRESENTATIVE FACTOR (R.F.) = DIMENSION OF DRAWING / DIMENSION OF OBJECT
= LENGTH OF DRAWING / ACTUAL LENGTH

>> LENGTH OF SCALE = R.F. * MAX. LENGTH TO BE MEASURED

TYPES OF SCALES


>>PLAIN SCALES ( FOR DIMENSIONS UP TO SINGLE DECIMAL)

PROBLEM 1 : Draw a scale 1 cm = 1m to read decimeters, to measure maximum distance of 5 m. Show on it a distance of 3 m and 4 dm.

Calculation R.F. 1cm/ 1m = 1/100 Length of scale = R.F. X max. distance = 1/100 X 500 cm = 5 cms

>>DIAGONAL SCALES ( FOR DIMENSIONS UP TO TWO DECIMALS)

PROBLEM 2 : The distance between Delhi and Agra is 200 km. In a railway map it is represented by a line 5 cm long. Find it’s R.F. Draw a diagonal scale to show single km. And maximum 600 km. Indicate on it following distances.
1) 222 km 2) 336 km 3) 459 km 4) 569 km

Calculation

RF = 5 cm / 200 km = 1 / 40, 00, 000 Length of scale = 1 / 40, 00, 000 X 600 X 105 = 15 cm

>>COMPARATIVE SCALES ( FOR COMPARING TWO DIFFERENT UNITS)

PROBLEM 3 : A motor car is running at a speed of 60 kph. On a scale of RF = 1 / 4,00,000 show the distance traveled by car in 47 minutes.

Calculation

Scale of km.

length of scale = RF X 60 km = 1 / 4,00,000 X 60 X 105

= 15 cm.