Cited for Emary A.B. (1981) Enlarging and Reducing Drawings. In: A Comprehensive Practical Geometry for Builders. Palgrave, London

1. 15. ENLARGING AND REDUCING DRAWINGS
Very often it is necessary to enlarge and sometimes to reduce
mouldings in size but it is also essential to retain their similarity.
Figures 134 and 135 show how it is possible to reduce and
enlarge irregular figures. Let a - b - c - d - e (figure 134)
be an irregular pentagon which has to be reduced in size so
that a - b is now a - b'. All the other sides of the figure
are to be reduced proportionately.
1. Draw the figure a - b - c - d - e.
2. On a - b mark b' making a - b' the required length.
3. Draw the diagonals a - c and a-d.
4. Draw b' - c' parallel to b - c, c' - d' parallel to c - d
etc., until the figure is complete.
c
Figure 134
Figure 135
Figure 135 is similar to the preceding one, but this time
a - b - c - d - e has been enlarged so that a - b now becomes
a - b' in length.
40
Figure 136 shows how an irregular shape can be either
enlarged or reduced in size. The original drawing is divided
up into squares and a similar quadrilateral to fit the reduced
or enlarged drawing is constructed and divided into a similar
number of squares. Then, by following the pattern of the
original drawing, using the squares for reference, the required
drawing can be completed.
Figure 136
-+ ---j-~-+-~-13
+----t-,I-I 5
2 3 4 5 6 2 3 4 5 6
ENLARGEMENT AND REDUCTION OF MOULDINGS
To enlarge a moulding (figure 137) in thickness only:
1. Draw the moulding a - b - c.
2. Project the various points across the width of the mould-
ing downwards and beyond the base line.
3. Project the various points through the thickness of the
moulding across to a-c.
4. Make a - e equal to the required thickness. Draw c - e
and the lines from f and g parallel to c - e.
5. With centre a and radii a - f', a - g' and a - e describe
the arcs round to a-d. Project the points thus obtained
to intersect with the vertical lines brought down from the
moulding to give various points on the required moulding.
A. B. Emary, A Comprehensive Practical Geometry for Builders
© A. B. Emary 1981

2. Enlarging and reducing drawings 41
Figure 137
Enlargement in width and thickness
Figure 138 shows how a moulding can be increased in width
as well as in thickness. Let a - b' - c' be the moulding and
a - b the required thickness and a - c the required width.
1. Draw the given moulding and also a - b and a - c of the
required moulding.
2. Draw b' - b and the other lines through the thickness
of the moulding parallel to b' - b. And similarly draw
c' - c and the other lines across the width parallel to
c' - c.
3. Lines from points on a - b should be drawn across to
meet lines brought down from a - c to give points on the
required moulding. CO
Figure 138
Proportional reduction
Figure 139 shows how a moulding can be reduced proportion-
ately. Let 0 - 1 - 2 - 3 - 4 - 5 - 6 be the given moulding
and 0' - 6' be the depth of the required moulding.
1. Draw the given moulding and some distance away draw
0' - 6' parallel to 0 - 6.
2. Draw a line from 0, through 0' in the direction of 0".
3. Draw another line, from 6, through 6' to meet the other
in 0".
4. Draw other lines from 1, 2, 3 etc., to meet in 0".
5. Draw 0' - 2' parallel to 0 - 2, 2' - 3' parallel to 2 - 3
etc., to complete the required moulding.
As it would be difficult to position accurately point number 4
in the required moulding point number 1 has been placed on
the given moulding immediately above 4. This will enable 4' to
be placed accurately.
Figure 139 6 5
ARCHITRAVES AROUND A DOORWAY
Figure 140 shows how the shapes of two architraves around
a doorway, unequal in width can be decided.
givlZn
mitre
a Figure 140