Router bit "drills" odd- and over-size holes
While building the mantel clock project from issue 194 (November 2009), I wanted a more precise method than jigsawing to fashion the 33⁄16 " hole for the clock movement. Here's the simple jig I came up with for easy odd-sized holes.
The jig consists of two scraps of plywood—the base sized to fit on your auxiliary drill-press table, the platform sized to rotate without hitting the drill-press column—and a 31⁄2 " long scrap of 4×4 lumber as a spacer.
Center, glue, and screw the spacer to the base, and the platform to the spacer. Next, drill a 3⁄8 " clearance hole, centered, through the platform.
After laying out the clock face on your workpiece, drill a 3⁄8 " hole through its center point. Mount the workpiece to the platform using a 3"-long, 3⁄8 " lag screw and washer, as shown, leaving the lag just loose enough so the platform turns freely.
With a 1⁄4 " spiral upcut router bit chucked in the drill press, clamp the base to the table, positioning it so the bit will cut just inside the marked circle on the workpiece. Set the depth stop to 1⁄4 " depth; then, with the drill press on its highest speed setting, lower the bit and turn the workpiece to complete the circle. Repeat the cut, lowering the depth stop an additional 1⁄4 " each pass to complete the cutout.
—Frank Rasberry, Bedford, Texas