A compass draws arcs and circles. One leg is sharpened to a point; a pencil attaches to
the other. An adjustable locking arm fixes the distance between the two legs, which
governs the radius of the curve.
Using a Compass
Compass scribing a circle:
Insert a sharp pencil into the tool's short leg. Set the distance between the two legs
to the desired radius, tighten the locking screw, and position the metal pivot point at
the center of the desired circle. Then swing the pencil over the surface. Use an inscribed
ruler to set the distance between the legs accurately and easily. Set the steel point
into the groove at the 1-inch mark and then set the point of the pencil in a groove at
the desired distance away. Remember to subtract 1 inch from the measurement.
Compass scribing an irregular edge:
To trace an irregular contour onto a piece of stock, set the legs of the compass to the
widest distance between the contour and the stock. While holding the point against the
contour and the pencil against the stock, draw the compass along the contour, keeping the
compass perpendicular to the stock.
Purchasing
A 6-1/2-inch compass can draw circles and arcs from 1/16 inch to 13 inches in diameter. An
optional extension bow adds another 6 inches. When selecting an inexpensive compass
without a locking screw, be sure the legs move stiffly so they won't slip out of
position.
Other Names
Bow compass
Substitutes
An alternative to the compass is a spring divider. This device's two hardened points are
used to scribe arcs and circles, mark straight or curved parallel lines, and transfer
measurements from one place to another. The identical legs are held in place with spring
tension; you reposition them by adjusting the knurled nut on top of the device. Spring
dividers are available in sizes up to 12 inches.
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