How do I make a large hole?
Hole-y dilemma, Batman!
Q: Every so often, I have a project that calls for making a hole larger than my largest holesaw. What is the best method for doing this?
—Randy Claxton, Mesa, Ariz.
A: Most holesaw sets max out at 2-1⁄2", Randy, although you can buy individual holesaws for diameters up to 6". For holes larger than that, or in between standard holesaw sizes, try one of these methods.
For holes up to about 8" in diameter, consider a circle cutter (also known as a wing cutter) in a drill press. A circle cutter features an adjustable arm that holds a cutter. Set the distance between the center of the pilot bit and the cutter's edge to the radius of the hole you want to drill (photo, above).
For workpieces too large for the drill press, use the wing cutter to make a template by cutting the hole in a scrap. Then, rough-cut the hole in the workpiece with a jigsaw. Secure the template over the hole with double-faced tape and complete the hole with a router and pattern bit (photo, below).
To cut larger holes, use a router and trammel jig. Purchase a jig or make your own from 1⁄4" hardboard or plywood. Drill a clearance hole near one edge of the jig for a 1⁄4" straight bit, and holes to mount your router. Using the radius of the hole you wish to make, measure from the far edge of the bit and drill a 1⁄4" hole near the other end of the jig. Insert a bolt, or glue a short length of dowel into the hole for a pivot pin.
To use the jig, drill a 1⁄4" hole in your workpiece and insert the jig's pivot pin into the hole. Turn on the router, and lower the bit into the wood 1⁄4" for the first pass (photo, below). Then lower the bit 1⁄4" and make another pass, repeating the procedure until you cut through the workpiece.
For less exacting jobs where you won't see the edge of the hole, a jigsaw makes quick work of cutting large holes. Lay out the hole circumference on your workpiece and drill a 3⁄8" starter hole on the inside edge. Then, insert the jigsaw blade into the hole and carefully cut along the line. With a steady hand, you can achieve reasonable accuracy.