The Family Handyman DIY Tip of the Day: Big Circle Cuts. To cut a circle, make a compass arm for your router from 1/4-in. plywood. Remove the router’s plastic base and drill corresponding holes in your compass arm. Attach the arm to your router and install a straight-cutting carbide bit. Pin the compass arm to the plywood with a 6d nail. The top of the finished circle should face down. Cut the circle in 2 or 3 passes.