SUBJECT: TECHNICAL DRAWING
CLASS : SS 1
TOPIC: ENLARGEMENT AND REDUCTION
Basically, the instrument used for enlargement and reduction is the scale rule. But it possible to do enlargement and reduction of small figures on paper by construction.
A. ENLARGING AND REDUCING A GIVEN LINE IN A GIVEN PROPORTION (E.g. 5:7 and 5:3)
1. Draw the given line AB ( say AB – 45).
2. At any convenient point P, fix the pole or peg.
3. Draw lines from P passing through A and B.
4. Divide one line into 7 equal parts such that AB lies on division 5.
5. Transfer AB to A1B1 on division 7 for enlargement and to A2B2 on division 3 for reduction.
B. REDUCING A GIVEN FIGURE IN A RATIO OF 5:3
1. Draw the given figure ABCDE.
2. Centre at B radius BA, draw a semicircle.
3. Using a division line BO, step off 5 units.
4. Join 5P and transfer to 3P1.
5. Bisect AP1 at X and centre at X radius XP, draw a semicircle.
6. Erect a perpendicular at B to get y and z.
7. Join zA and transfer to yA1. 8. Transfer all the lines from AE to A1E1, ED to E1D1,and DC and D1C1.