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 lining (sometimes called diagonal hatching or crosshatching) 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.

horizontal would be parallel or perpendicular (or nearly so) to a prominent visible outline, the angle should be changed to 30°, to 60°, or some other angle. If two adjacent sectioned surfaces are shown, the hatching should be in opposite directions, as shown in figure 5-34, view B. If still a third surface is included, it should be hatched at another suitable angle to make the surface clearly stand out separately from the other surfaces (figure 5-34, view C). Note that the hatching lines on one surface are not permitted to meet those on an adjacent surface.

In drawing section lining, use a sharp, medium-grade pencil (H or 2H). Space the lines as uniformly as possible by eye. As a rule, spacing of the lines should be as generous as possible, yet close enough to distinguish the sectioned surface clearly. For average drawings, space the lines about 3/32 in. or more apart.

Diagonal hatching on an auxiliary section should be drawn at 45 degrees to the horizontal, with respect to the section. Figure 5-35 shows this rule.

In a revolution or other view of an object in other than the normal position, the diagonal hatching on a section should be drawn at 45 degrees to the horizontal or vertical axis of the object as it appears in the revolution. Figure 5-36 shows this rule.

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