Comprising two hardwood dowels and a center block, this adjustable jig allows your router to cut circles of virtually any diameter. The jig is assembled by slipping the dowels into the accessory holes in the router base plate, fixing the dowels to the block, and attaching the block to the center of the circle marked on the workpiece. With wood cleats holding the stock to a work surface, the router bit is aligned with the end of the circle’s marked radius and the screws that clamp the dowels to the base plate are tightened. The circle can then be routed.
To cut larger circles than most commercial guides allow, use the compass jig shown at right. Make the device from Winch hardboard, sizing it to suit your router. The router end of the jig should be circular and about the size of your tool’s base plate. Make the arm at least 2 inches wide and longer than the radius of the circle you will be cutting. Bore a hole in the center of the rounded end for the router bit. To mount the jig on your router, remove the sub-base and center the bit over the clearance hole. Mark the screw holes on the jig, bore and countersink them, then screw the jig to the router. Draw a line down the center of the jig arm and mark the radius of the circle on it, measuring from the edge of the bit. Drill a hole at the center mark and screw the jig to the workpiece. Secure the stock to the work surface with cleats. Plunge the bit into the stock and rout the circle in a clockwise direction.