DIMENSION LINES

Engineering Aid 3 - Beginning Structural engineering guide book
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the incorrect procedure is shown in the lower views. Figure 3-28 shows an intersection between a hidden edge line and a visible edge line. Obviously, on the object itself the hidden edge line must be below the visible edge line. You indicate this face by drawing the hidden edge line as shown in the upper view of figure 3-28. If you drew it as indicated in the lower view, the hidden edge line would appear to be above, rather than beneath, the visible edge line. Figure 3-29 shows an intersection between two hidden edge lines, one of which is beneath the other on the object itself. You indicate this fact by drawing the lines as indicated in the upper view of figure 3-29. If you drew them as indicated in the lower view, the wrong line would appear to be uppermost. EXTENSION LINES Extension lines are used to extend dimensions beyond the outline of a view so that they can be read easily. These thin, unbroken lines are started about one sixteenth of an inch from the outline of the object and extend about one eighth of an inch beyond the outermost dimension line. They are drawn parallel to each other and perpendicular Figure 3-29.-Correct and incorrect procedures for draw- ing intersecting hidden edge lines that are on different levels. Figure 3-30.-Use of extension lines. to the distance to be shown. (See fig. 3-30.) In unusual cases, extension lines may be drawn at other angles if their meaning is clear. As far as practical, avoid drawing extension lines directly to the outline of an object. When it is necessary for extension lines to cross each other, they should be broken, as shown in figure 3-31. DIMENSION LINES A dimension line, terminating at either end in a long, pointed arrowhead, is inserted between each pair of extension lines. It is a thin line, and, Figure 3-28.-Correct and incorrect procedures for draw- except in architectural ing a hidden edge line that intersects a visible edge is usually broken to line. dimension numerals. 3-22 and structural drafting, it provide a space for the Occasionally, when the

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