Scale Drawing – JSS3 Basic Technology Lesson Note (First Term)

TOPIC: SCALES AND SCALE DRAWING, SIMPLE BLUE PRINT READING

CONTENT

1. DEFINITION OF SCALE DRAWING
2. MATERIALS AND INSTRUMENTS FOR SCALE DRAWING
3. TYPES OF SCALE DRAWING
4. MEASURING AND COMPARING GIVEN SIZES
5. SIMPLE DETAILS OF A BUILDING PLAN
6. COMMON SYMBOLS USED AND THEIR INTERPRETATIONS

 DEFINITION OF SCALE DRAWING

Scale drawing can be defined as the accurate representation of objects in a determined proportion .Scale drawing is different from ordinary drawing in that it presents the object either reduced or enlarged. There are scales for reduction and for enlargement of the size of the object.

 MATERIALS AND INSTRUMENTS FOR SCALE DRAWING

1. Metric rule

This has two flat straight edges. It is usually 30cm long. Each main division on the metric rule is equal to one centimeter (1cm =10mm) and each division is sub divided into 10 units being 1mm .Always start from 0 as the beginning of your measurement.

2. Scale rule 

These have three straight edges and are triangular in shape. Each edge is graduated and each scale designation is marked on the rule.

 EVALUATION  

• Define scale drawing.
• State the materials and instruments for scale drawing.

 SCALE 

Some objects are too big for the actual size to be contained on a drawing paper, while some are too small for the parts to be clearly seen. Hence, such objects should be drawn to an appropriate scale.

Scale is usually given as a ratio and they are stated in the title block.

 TYPES OF SCALE DRAWING

A scale is used to draw or read a scale on a drawing paper

We have the following scales:

1. Full scale  drawing 
2. Reduced scale drawing
3. Enlarged scale drawing

Therefore a cupboard of size 1800mm long drawn as 18mm has a reduced scale drawing of 1:100mm.

 ENLARGED SCALE DRAWING 

This is used when the object to be drawn   is too small to be clearly seen.Here, the actual size of the object is enlarged in the proportion to the drawing.

Examples include 2:1, 10:1, 100:1,  

 Drawing size          100:1            actual size

 REDUCED SCALE DRAWING: this is used when the object to be drawn is too big. Here the actual size of the object is reduced in the proportion of the drawing. Examples include 1:2, 1:5, 1:10, 1: 100 etc.

 FULL SCALE DRAWING: This is when the object to be drawn is the same size as the size of the object the scale used is 1:1.

 EVALUATION

1. Define scale drawing.
2. Mention three types of scale drawing.