WHENcutting out a hole in metal it is not necessary always to cut out all the metal in the form of chips and shavings. The most economical method is to cut out a piece of a desired diameter after the fashion of a surgeon when trepanning a skull. The accompanying illustration shows a method of doing this work. The drill consists of a shank provided with a reduced threaded portion and with a still further reduced projection, serving as a pivot. The plate A trepanning drill. mounted on the shank is clamped in place by means of a nut which holds it securely against the shoulder of the shank. The plate is provided with a square aperture in which the tool is secured. The pivot of the drill is fitted into a small hole drilled in the center of the circle which is to be cut out. Then by driving the cutting tool into its socket and turning the shank, a circular slot will be made removing the metal in the form of a disk and leaving a hole of the desired diameter.