Special Cased Instruments
Special cased instruments are uncommon drawing tools used for distinct
purposes. They are more delicate than standard cased instruments,
For drawing circles and arcs that are less than 1 inch in diameter, use bow
instruments. These delicate instruments have a side thumbscrew adjustment
that controls the diameter of the circle. There are primarily four types of
bow instruments. They are a bow pen, a bow pencil, a bow divider, and a
special tool, called a drop bow pen. A drop bow pen is for drawing circles
and arcs less than one fourth-inch in diameter. It has a rotating center shaft
that moves up and down to minimize motion during drawing.
Figure 2-29 shows bow instruments.
Figure 2-29. Bow instruments.
Keep bow instruments clean and free of debris. Do not store dirty pen nibs.
Wipe bow instruments with a light oil cloth and store them in the case when
they are not in use.
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