You can make square holes in wood with an ordinary chisel. Square holes can be used as the counterpart for the traditional mortise and tenon joint, for a craft project or to reproduce an old-fashioned technique found in turn-of-the-century woodworking. To get square holes straight, a drill press is used to drill a pilot hole, followed by hand carving the sides of the hole with an appropriately sized chisel. Start out by cutting a perfectly square 3/4-by-3/4-inch hole through a piece of poplar.
Insert a 3/4-inch brad-tipped drill bit into a drill press. Place the poplar under the bit. Turn on the drill press and drill through the poplar.
Place a tri-square along one side of the hole. Use the tri-square to draw perfectly square lines around the perimeter of the hole.
Place the tip of the chisel on one of the lines. Aligning it with the line, tap on the end of the chisel with a mallet to establish the line. Do this on all four sides.
Place the chisel vertically on one of the lines. Tap hard on the chisel to drive it down through the hole, cutting the sides of the hole square as it penetrates into the hole. Do this on all four sides.
Shave and trim the sides of the hole with the chisel until they are smooth and clean.
For the cleanest square hole, sharpen the chisel before using it.
Wear safety glasses while making this cut.