Cased Instruments, ContinuedCompassesUse a compass to draw arcs and circles. A standard compass is 6 inches longand it has two legs. One leg holds the needlepoint and the other leg holds thenib. The nib may be a pen nib, a pencil attachment, or another needlepoint.The legs are often jointed above the nib to maintain perpendicularity to thedrawing surface. The joint also reduces uneven wear and friction to the nib.To draw a circle larger than 12 inches, add an extension bar at the joint.Figure 2-23 shows a pivot joint compass.Figure 2-23. —A pivotjoint compass.The type of hinge on a standard compass indicates the quality of theinstrument and its ability to hold a set. There are three types of hinges.Figure 2-24 depicts the three types of compass hinges.Figure 2-24.-Compass joints.Continued on next page2-23
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