Enlarge holes in two easy steps
Maybe you need to enlarge a hole, or make a dead-on round hole larger than your largest Forstner bit. Do either using a rabbeting and a flush-trim bit. To enlarge a hole’s radius by 1⁄4 ", first rout a 1⁄4 "-deep rabbet the width of your cutter while keeping the bearing against the edge of the hole. This creates the “step.”
Next, turn the workpiece upside down and install a flush-trim bit. Adjust the cutting depth so the bearing rides along the cut made by the rabbeting bit and rout away the step.