SUBJECT : BASIC TECHNOLOGY
CLASS : JSS 3
TOPIC : SCALES AND SCALE DRAWING
The scale drawing is a process by which the size of an object can be increased or decreased.
SCALES.
Scales: A scale is a means of reducing or enlarging measurements or dimensions. The scale is used so that large objects can use so that large objects can fit into the drawing sheet during drawing.
If the scale is 1cm = 10cm, then every 10m of the real figure is represented by 1cm on the scale drawing. Hence 10m on the scale drawing represent 10 x 10 = 100m.
Also 2.5m on the scale represents 2.5 x 10m = 25m.
In another way, if a scale of 1cm = 5km on a Map, it means that 5km will be represented by 1cm on the scale.
Types of Scales:
There are three types of scales in use.
1) The Full Scale: 1:1 represent an object drawn full size.
2) The Reduced Scale: The reduced scale is used when the size of the object is too big to draw. For example: Let us consider the scale 1:100 this means that every 1mm on the drawing represent 100mm on the actual size of the object.
The examples of reducing scale ratios are 1:2, 1:10, 1:50, 1:100 etc.
1:2 represent an object drawn (1/2) the full size.
1:10 represent an object drawn (1/10) the full size.
3) The Enlarged Scale: The enlarged scale is used when the size of the object is too small to be clearly drawn.
For example: Let us consider the scale 100:1 this means that every 100mm on the drawing represent 1mm on the actual size of the object.
The examples of enlarged scale ratios are 2:1, 10:1, 50:1, 100:1 etc.
2:1 represent an object drawn twice the full size.
10:1 represent an object drawn ten times the full size.
Note:
Scale drawings are given in ratios. A scale 1:50 means that every 1mm on the drawing represent 50mm on the size of the object.
SCALE MULTIPLIER
Scale multiplier and divisor of 2:5:10 are recommended. The representative fractions of the commonly used scales are:
1:1 means full size
1:2 means half full size
1:5 means one-fifth full size
1:10 means one-tenth full size
2:1 means twice full size
5:1 means five times full size
10:1 means ten times full size
Example 1:
In a scale of ratio 1:4, if the actual length of the object is 200m, what is the length of the scale used?
Solution:
Ratio 1:4 is a reduced scale.
1mm represents scale drawing.
4mm represents object length.
200m is the object length.
?mm represents scale drawing.
This implies that:
1mm on the scale drawing = 4mm object length
? = 200mm object length
This means that:
4mm on object = 1mm on scale
1mm on object = ¼
200mm on object = ¼ X 200
= 50mm
Example 2:
The scale drawing of the length of the advertisement bill board measures 5cm, what is the actual length of the bill board, if the scale is 1cm represent 2m?
Solution:
1cm represents 2m
…5cm will represent 5 X 2 = 10m
The actual length of bill board = 10m
ASSIGNMENT:
1) Define scale drawing.
2) Mention the types of scale drawing.
3) Explain the three types of scale drawing.
4) In a scale of ratio 1:4, if the actual length of the object is 200m, what is the length of the scale used?
5) Explain the scale multiplier.