Page 30 - Engineering drawing from first principles using AutoCAD

First steps 23

Table 1.2

Applications Drawing sheet size Minimum character
height (mm)

Drawing numbers etc. AO,A1,A2,A3 7
Dimensions and notes A4 5
AO 3.5
A1,A2,A3,A4 2.5

Dashed lines start and finish with a dash in contact with connecting outlines or other
hidden lines. Dashes meet at corners and junctions where changes in direction occur. A
dashed line joining a curve should start with a dash at the tangency point.

Chain lines are drawn with long and short alternate dashes and start and finish with a
long dash. Generally the proportions of chain and centre lines should be adjusted so that
they appear to be balanced and symmetrical if possible. Centre lines extend a short
distance beyond an outline. If centre lines cross they should be arranged to intersect
on a line rather than in the space.
Where centre lines define a circle centre, the centre point should be defined by crossing
lines. Where a succession of holes are drawn, the centre lines appearance can often be
improved by drawing one hole with its centre lines and using the COpy or ARRAY feature
to repeat as required.

Minimum character height proportions are given in Table 1.2. All dimensions and notes
have been drawn with a minimum character height of 3.5mm and this is meant to take
into account the fact that some drawings need to be reduced in size to fit a book page.
Roman Duplex is the text style selected with a width factor of 0.9. This width factor
reduces the width of notes by about 10 per cent when compared with a width factor of 1.
Please also refer to Chapter 5 regarding text applications.

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Figure 1.21