3

Line Conventions

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1 Introduction

Engineering drawing is the art of combining different types of

lines to give a representation of an object. Each line has a defi-

nite purpose and sense to convey. It is therefore essential for

people involved with engineering drawing to have a clear un-

derstanding of the difference between the various types of

lines.

After completion of this chapter, students should be able to ap-

ply standard line practices while making engineering drawings.

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2 The Alphabet of Lines

The alphabet of lines is a set of standard line-types estab-

lished for technical drawing. The diagram that follows shows

the alphabet of lines, and the approximate dimensions used to

create different line types.

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3 Hidden Lines

Hidden features are represented as dashed lines, using

ANSI/ISO/BS standards line types:

Dashed lines are used to represent such hidden features as:

Holes

Surfaces

Change of planes

Example:

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Drawing convention for hidden lines:

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4 Centre Lines

Centre lines are alternating long and short thin dashes and are

used for:

the axes of symmetrical parts and features

bolt circles, and

paths of motion

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Centre lines should not terminate at another line or extend be-

tween views.

Very short, unbroken centre lines may be used to represent the

axes of very small holes.

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5 Order of priority of coinciding lines

When two or more lines of different types coincide, the follow-

ing order of priority should be observed:

a Visible outlines and edges (Continuous thick lines)

b Hidden outlines and edges (Dashed line)

c Cutting planes (Chain thin, thick at ends and changes of cutting planes)

d Centre lines and lines of symmetry (Chain thin line)

e Centroidal lines (Chain thin double dashed line)

f Projection lines (Continuous thin line)