When you go to a museum, you often see artefacts that have been
cut up. For example, to illustrate how a petrol engine works, the
cylinder block can be cut in half and the cut faces are invariably
painted red. In engineering drawing, cross-hatching is the equivalent
of painting something red. It is used to show the internal
details of parts which otherwise would become too complex to show
or dimension.
The cross-hatch lines are usually equi-spaced and, for small parts,
cover the whole of the 'red' cut area. They are normally positioned
at 45 ~ but if this is awkward because the part itself or a surface of it is
at 45 ~ , the hatching lines can be at another angle. Logical angles
like 0 ~ 30 ~ 60 ~ or 90 ~ are to be preferred to peculiar ones like 18 ~
(say). If sectioned parts are adjacent to each other, it is normal to
cross hatch in different orientations (+ and -45 ~ or if the same
orientation is used, to use double lines or to stagger the lines.
Examples of single and double + and --45 ~ cross-hatching lines are
shown in the vice assembly drawing in Figure 3.1. An example of
staggered cross-hatching is shown in the inverted plan drawing of
the movable jaw in Figure 3.2.
If large areas are to be sectioned, there is no particular need to have
the cross-hatching lines covering the whole of the component but
rather the outside regions and those regions which contain details.
When sections are taken of long parts such as ribs, webs, spokes of
wheels and the like, it is normally the convention to leave them
unsectioned and therefore no cross-hatch lines are used. The reason
for this is that the section is usually of a long form such that if it were
hatched it would give a false impression of rigidity and strength. In
the same way it is not normal to cross hatch parts like nuts and bolts
and washers when they are sectioned. These are normally shown in
their full view form unless, for example, a bolt has some specially
machined internal features such that it is not an off-the-shelf item.
Example of threads that are not cross-hatched can be seen in the
vice assembly drawing in Figure 3.1.
Engineering Drawing for Manufacture
by Brian Griffiths
· ISBN: 185718033X
· Pub. Date: February 2003
· Publisher: Elsevier Science & Technology Books
by Brian Griffiths
· ISBN: 185718033X
· Pub. Date: February 2003
· Publisher: Elsevier Science & Technology Books
