The standard ISO 128:1982 gives 10 line types that are defined A to
K (excluding the letter I). The table in Figure 3.4 shows these lines.
The line types are 'thick', 'thin', 'continuous', 'straight', 'curved',
'zigzag', 'discontinuous dotted' and 'discontinuous chain dotted'.
Each line type has clear meanings on the drawing and mixing up
one type with another type is the equivalent of spelling something
incorrectly in an essay.
The line thickness categories 'thick' and 'thin' (sometimes called
'wide' and 'narrow') should be in the proportion 1:2. However,
although the proportion needs to apply in all cases, the individual
line thicknesses will vary depending upon the type, size and scale of
the drawing used. The standard ISO 128:1982 states that the
thickness of the 'thick' or 'wide' line should be chosen according to
the size and type of the drawing from the following range: 0,18;
0,25; 0,35; 0,5; 0,7; 1; 1,4 and 2mm. However, in a direct contradiction
of this the standard ISO 128-24:1999 states that the thicknesses
should be 0,25; 0,35; 0,5; 0,7; 1; 1,4 and 2mm. Thus
confusion reigns and the reader needs to beware! With reference to
the table in Figure 3.4, the A-K line types are as follows.
The ISO type 'A' lines are thick, straight and continuous, as shown
in Figure 3.5. They are used for visible edges, visible outlines, crests
of screw threads, limit of length of full thread and section viewing
lines. The examples of all these can be seen in the vice assembly
detailed drawings. These are by far the most common of the lines
types since they define the artefact.
The ISO type 'B' lines are thin, straight and continuous, as shown
in Figure 3.6. They are used for dimension and extension lines,
leader lines, cross hatching, outlines of revolved sections, short
centre lines, thread routes and symmetry ('equals') signs.
Engineering Drawing for Manufacture
by Brian Griffiths
· ISBN: 185718033X
· Pub. Date: February 2003
· Publisher: Elsevier Science & Technology Books
