Instead of cutting circles with my handheld router, I use my table-mounted router and the simple slide-on auxiliary top as shown. The sliding top not only enables me to make the cut in safe increments without stopping to raise the bit, but also to adjust the circle’s size without repositioning the pivot nail.
To make this jig, cut a piece of ¼" hardboard slightly wider than your router tabletop and attach a pair of side cleats and stop cleat as shown. (Position the stop cleat so that the router bit grazes the inside edge.) Using the cut made by the bit, measure your desired radius, then drill a hole through the hardboard and insert a finish nail to serve as a pivot point. To rout a circle, place your workpiece on the pivot point and rotate it counterclockwise as you gradually slide it, and the table, into the bit. To rout a larger circle with the same pivot point, attach a clamp to the edge your router table to stop the front edge of the sliding table.
