Posted by
Easy WoodCraft on
Feb 29, 2016
A compass is useful in the shop for laying out circles and arcs. The most common types are the bow compass and the wing compass. The bow compass is a drafting tool with a threaded shaft that runs between the legs held together with a spring on top. One leg holds a steel point, the other a pencil lead. The legs of a wing compass are hinged at the top or joined with a spring and forced open or closed by turning a knurled knob that attaches to a threaded post that spans the legs. One leg has a steel point and the other is often designed to hold a standard pencil.
Drawing circles
I like to set my compass with a steel rule. I set the steel point into the etched graduation at the 1" mark and then adjust the drawing point to the desired radius (plus 1"). Although the steel point of a compass generally does an adequate job of holding its place, I've found that making a slight starter hole with an awl helps keep the point from wandering as the compass is rotated to mark the circle or arc.
Dividing circles
Here's a quick way to convert a circle to a hexagon or lay out six equally spaced holes (such as for spindles or mounting holes). With the compass still set to the desired radius, place the steel point on the perimeter of the circle and rotate the compass until it scribes a mark across the perimeter. Then move the steel point to this location and scribe another mark. Continue like this all the way around the circle—you'll end up where you started.
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