10 Drawings and rods
size, or this can be thought of as 1mm on the drawing
equalling 10mm in reality.
Although a scale rule is useful when reading draw-
ings, because of the dimensional instability of paper,
preference should always be given to any written
dimensions displayed on the drawing.
Finally, scaled drawings not only mini-
mize a designer/draughtsman’s project to fit
commercially- sized, manageable sheets of paper,
they also serve to convey an important sense of
proportion; i.e. if a scaled project looks dispropor-
tionate on paper, then common sense should tell us
that the full- size completed project will look dispro-
portionate.
EXPRESSING DIMENSIONS
CORRECTLY
The abbreviated unit symbol for metres is a small
(lower case) letter m; and letters mm for millimetres.
Symbols are not finalized by a full stop and do not use
the letter ‘s’ for the plural. Confusion occurs when, for
example, 4½ metres is written as 4.500 mm – which
means, by virtue of the decimal point in relation to the
unit symbol (mm): 4½ mm! To express 4½ metres, it
should have been written as 4500mm, 4.5m, 4.50m,
or 4.500m. Also, either one symbol or the other (m
or mm) should be used throughout on drawings;
they should not be mixed. Normally, whole numbers
should indicate millimetres; and decimalized numbers,
to three places of decimals, should indicate metres.
Contrary to what seems to be taught in schools,
the construction industry in the UK does not use
centimetres. All references to measurement are made
in millimetres and/or metres; i.e. 5 cm should always
be expressed as 50 mm.DIMENSIONING SEQUENCE
Figure 2.2: The recommended dimensioning sequence is
illustrated below. Length should always be given (or
written) first, width second and thickness third. For
example, a particular length of timber might be 1500 ×
150 × 25 mm. However, if a different sequence is used,
it should be consistent throughout.Figure 2.1 Commonly used
metric scales 1:5, 1:10, 1:20,
1:50 and 1:100.ABCFigure 2.2 Dimensioning sequence should be A × B × C.1: (^100) 5öO 5öO
0 1m (^2 3 4 51) m
1: 50 250 500 750 250 500 750 250 500
0 1 m 2m
1: (^20 100 300 500 700 )
0 1 m
1: (^10 50 100 200 300 400) 500mm
0
1:5 25 50 75 100 200mm
0