Making square holes in wood most often involves a mortising machine. However, the broach, a machinists tool, can accomplish the same function better and more quietly. It will produce a perfectly square, smooth 1/2" hole in any location where a round hole can be drilled providing that the hole is a through hole. Just drill a round hole with a diameter equal to the dimensions of the desired square. Then insert the broach in the hole and either drive it through with a brass hammer or push it through with your drill press, always backing it with a piece of scrap to prevent splintering on the back side.