I was wondering if anyone knew of a method to drill concentric counterbores on both sides of a rectangular block of acrylic with a through hole? I've tried one method of drilling a counterbore one side and then drilling a hole through the center. Then flipping the piece and placing its hole through the drill bit to center it and clamp it down before doing another counterbore. This method works okay, but I was wondering if anyone knew of a more efficient method that gives better results?