Adjustable compass swings wide for big arcs

When laying out the semicircle on the backrest of an Adirondack chair, I found I needed a compass. A big one.

Here's how to build an adjustable beam compass that fits the bill: First, cut and rabbet two pieces of scrap hardwood to fit inside a length of aluminum T-track. Drill a ³⁄₁₆ " hole in each piece and twist in a length of ¹⁄₄ "×20 threaded rod. On the opposite end of one piece, drill a hole to snugly fit a pencil. In the other piece, drive a screw to serve as a trammel point. Slide the scraps into the T-track and tighten them with a fender washer and T-knob.

After setting the distance between the pencil and screw to the needed radius, I scribed a perfect sweeping top on my project.
—Gary Dean, Prince George, B.C.