The widths and construction of the lines you use in making a drawing are
important to interpreting the drawing. DOD-STD-100 series states that on
drawings, the actual widths of each type of line is governed by the size and
style of the drawing. Good resolution for each type of line is important for
maximum reproductive clarity.
Line configurations and the meanings assigned to these configurations are
known as line conventions. Line conventions convey information as
succinctly as a physical example of the object itself. The appropriate use of
standard line conventions enables fabricators to replicate objects based solely
on your drawing.
Lines that indicate the center of an object or shape are called centerlines.
Centerlines are often the first lines drawn and serve to position images on
paper. Sometimes, measurements use centerlines as a common point of
reference. Centerlines may also indicate the travel of a moving center.
Centerlines are drawn by alternating evenly-spaced long and short dashes.
They extend a minimum of 1/4" beyond the object outline. At points of
intersection, they appear as short dashes. If there is no possibility of
confusion, you may draw only the short centerlines (a single dash) rather
than the entire length of the line.
Figure 3-6 shows examples of centerlines.
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