Drawing scales

Small objects are sometimes drawn larger than actual size, while large components and assemblies, of necessity, are drawn to a reduced size. A drawing should always state the scale used. The scale on a full-size drawing will be quoted as 'ORIGINAL SCALE 1:1'.

Drawings themselves should not be scaled when in use for manufacturing purposes, and warnings against the practice are often quoted on standard drawing sheets, e.g. 'DO NOT SCALE' and 'IF IN DOUBT, ASK'. A drawing must be adequately dimensioned, or referenced sufficiently so that all sizes required are obtainable.

The recommended multipliers for scale drawings are 2, 5, and 10.

1:1 denotes a drawing drawn full-size.

2:1 denotes a drawing drawn twice full-size.

5:1 denotes a drawing drawn five times full size. Other common scales are 10:1, 20:1, 50:1, 100:1, 200:1, 500:1, and 1000:1.

It should be pointed out that a scale drawing can be deceiving; a component drawn twice full-size will cover four times the area of drawing paper as the same component drawn full-size, and its actual size may be difficult to visualize. To assist in appreciation, it is a common practice to add a pictorial view drawn full-size, provided that the drawing itself is intended to be reproduced to the same scale and not reproduced and reduced by microfilming.

The recommended divisors for scale drawings are also 2, 5, and 10.

1:1 denotes a drawing drawn full-size. 1:2 denotes a drawing drawn half full-size. 1:5 denotes a drawing drawn a fifth full-size. Other common scales used are 1:10, 1:20, 1:50, 1:100, 1:200, 1:500, and 1:1000.

The draughtsman will select a suitable scale to use on a standard drawing sheet and this will depend on the size of the object to be drawn. Remember that the drawing must clearly show necessary information and detail. It may be beneficial to make a local enlargement of a small area and an example is given in Fig. 7.15.

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