sectional view. These lines are omitted by general
custom, the custom being based on the fact that
the elimination of hidden lines is the fundamental
reason for making a sectional view. However, any
lines that would be VISIBLE behind the sectional
plane of projection must be included in the
sectional view.
The section shown in figure 5-31 is called a
FULL SECTION because the cutting plane passes
entirely through the object and divides it into two
equal parts. Also, the object shown in figure 5-31
is a symmetrical object—meaning, in general,
that the shape of one half is identical to the
shape of the other. This being the case, you could
have used a HALF SECTION like the one shown
in figure 5-32. This half section constitutes one
half of the full section. Because the other half of
the full section would be identical with the half
shown, it need not be drawn.
Note that a center line, rather than a visible
line, is used to indicate the division between the
sectioned and the unsectioned part of the sectional
view. A visible line would imply a line that is
actually nonexistent on the object. Another term
used in place of center line is LINE OF
SYMMETRY.
A section consisting of less than half a
section is called a PARTIAL SECTION. (See
fig. 5-33.) Note that here you use a break line to
indicate the division between the sectioned and
unsectioned part. For this reason, a partial
section is often called a BROKEN SECTION.
The section lines drawn on a sectional surface
always serve the basic purpose of indicating the
limits of the sectional or cutaway surface. They
may also indicate the type of material of which
Figure 5-32.-Use of half section.
Figure 5-33.-Use of partial or broken section.
the sectioned surface consists. For example, in
figure 5-34, view A shows section lining for an
object made of cast iron. View B shows two
matching parts made of steel, and view C shows
three adjacent parts made of brass, bronze, or
copper. For other symbolic section lining symbols,
refer to ANSI Standard Y14.2.
In view of the vast numbers of different
materials, and since drawings must always
identify materials by lettered form, such as notes,
it is usually more desirable, and it is common
practice, to use a general purpose symbol for
section lining. The general purpose symbol is the
cast iron symbol shown in figure 5-34, view A.
The use of other symbols, then, should be limited
to those situations when it is truly desirable, or
conventional, to graphically differentiate between
materials. For example, in an assembly drawing
(a drawing showing different papers fitted
together), it is often desirable to differentiate
materials.
On a regular multi-view section, section lin-
ing (sometimes called diagonal hatching or cross-
hatching) should be drawn at 45° to the
horizontal, as shown in figure 5-34, view A.
However, if section liners drawn at 45° to the
Figure 5-34.-Diagonal hatching on separate sectional
surfaces shown in normal position.
5-19
