I was hanging drywall in a den next to my kitchen recently and was using a rotary cutting tool with a guide-point bit to make cutouts around electrical boxes, doors, and windows. The tip of these bits is smooth, so it can ride harmlessly along the side of a switch box or door jamb while the cutting grooves farther up the bit go through the drywall. Because you can’t see what’s guiding the bit behind the drywall, you have to rely on the feel of the bit pressing against the guiding surface.
At one point, I found myself needing to make a large cutout for a pass-through opening between the den and the kitchen. The existing edge of the opening that would provide the guiding surface for the rotary bit was finished drywall. Even though the end of the rotary bit is smooth, it still does a fair amount of damage to any soft surface and even digs into drywall in some cases. My father, Ralph Langdon, who gets credit for this tip, suggested using a thin, flat metal edge to provide a firmer surface against which the tip of the rotary bit could ride as we cut the opening.
It turns out that we had just the thing on site as part of our drywall-finishing supplies. It’s called paper-face metal drywall tape. This product is sold in rolls and is similar to standard drywall tape except that it has two thin strips of aluminum running down its length. Typically, it’s bent 90° down its length to provide a crisp metal edge for inside or outside drywall corners.
This tape can easily be cut to length, then cut in half lengthwise, leaving a thin metal strip against which a rotary bit can ride without damaging the drywall beneath. The back edge of the strip, away from the cutting bit, is drywall tape, so a few pieces of masking tape can hold it in place, even on a ceiling.
It’s quick and cheap to apply this tape as a guide, and the resulting cuts don’t damage the underlying drywall. The same technique could be used to protect finished woodwork or any other soft surface, and because the metal is so thin and flexible, it could even be used as a guide along a curved edge.
Greg Langdon, Louisville, KY
From Fine Homebuilding 200, pp. 28
November 12, 2008