An inexpensive and simple jig quickly and accurately pinpoints the center of a circle. Cut a 90° notch from 3⁄4 " stock. Screw a straightedge over the notched base, as shown, to create a 45° angle. Place the circle against the guide and scribe one line. Rotate the circle about 60° and mark another line. To check the accuracy, rotate the circle once more. If the lines form a small triangle, the center is inside the triangle.
—George Harenberg Chincoteague, Va.