Use of the Compass

about one grade softer than the pencil used for corresponding line work. For dim construction lines, use 4H to 6H leads. Avoid using leads that are too short. The compass lead should be sharpened with a single elliptical face, as shown in figure 3-7, view A. A sandpaper pad works best for sharpening compass leads. The elliptical face of the lead is normally placed in the compass so that it faces outward from the other compass leg. Adjust the shoulder-end needlepoint so that the point extends slightly farther than the lead (fig. 3-7, view B). With the needlepoint pressed lightly in the paper, the compass should be centered vertically when the legs are brought together. Bow compasses and pivot joint compasses are used in the same manner. To draw a circle with a compass, lightly press the needlepoint into the drawing paper and rotate the marking leg around it. Always rotate the compass clockwise. As you rotate, lean the compass slightly forward. With a little practice, you will find that you can easily draw smooth circles using only the thumb and forefinger of one hand. It is important that you use an even pressure as you rotate the compass. You may find it necessary to rotate the compass several times to produce a circle with a uniform dense black line. When you wish to set the compass to draw a circle of a given diameter, use a piece of scratch paper and follow the steps listed below, referring to figure 3-8. 1. Draw a horizontal line with a straightedge. 2. With the straightedge as a base, use a triangle and draw a vertical line intersecting the horizontal line (fig. 3-8, view A). 3. Measure the radius of the circle with a scale, as shown in figure 3-8, view B, and draw a second vertical line from this point. 4. Set the needlepoint at the intersection of the first vertical line and the horizontal line (fig. 3-8, view C). This is the center of the circle. 5. Set the marking leg to fall on the intersection of the second vertical line and the horizontal line (fig. 3-8, view D). 6. Draw a half circle with the compass fig. 3-8, view E). 7. Check your diameter established (fig. 3-8, view F). work by measuring the by this half circle with a scale Figure 3-8.-Drawing a circle of a given radius. 45.157 Once You have set the compass to the exact radius of the circle, handle it very carefully so that you don’t disturb the setting. Set the needlepoint at the center of the circle and carefully rotate the compass to draw a line describing the circumference of the circle. Do not apply too much pressure on the needlepoint or it will bore a hole in the paper and you will lose the accurate center mark. To keep the diameter of the hole to a minimum, you may set the needlepoint of the compass on a small strip of paper or thin cardboard over the drafting sheet at the center of the circle. When you are using the pencil leg to draw circles smaller than 1 in. in radius, keep the adjustable pencil and needle legs straight. For larger circles, both legs should be adjusted so that they are perpendicular to the paper. On the other hand, when you are using the compass with the pen leg, you MUST adjust it at the hinge joint to keep it perpendicular to the paper for all size 3-7