Special Cased InstrumentsIntroductionSpecial cased instruments are uncommon drawing tools used for distinctpurposes. They are more delicate than standard cased instruments,BowFor drawing circles and arcs that are less than 1 inch in diameter, use bowinstrumentsinstruments. These delicate instruments have a side thumbscrew adjustmentthat controls the diameter of the circle. There are primarily four types ofbow instruments. They are a bow pen, a bow pencil, a bow divider, and aspecial tool, called a drop bow pen. A drop bow pen is for drawing circlesand arcs less than one fourth-inch in diameter. It has a rotating center shaftthat 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 whenthey are not in use.Continued on next page2-27
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