PUNCH, a tool for cutting circular or other shaped pieces out of metal, wood, or other materials. The simplest form of this instrument consists of a piece of steel formed at one end into a hollow cylinder, the end of which is ground to a very sharp cutting edge. The other end of the punch is made strong and thick, to receive blows from a hammer, and to serve as a handle. When the instrument is in use, the cutting edge is applied to the surface which is to be perforated, and a blow sufficiently hard is struck on the end of the handle. when a circular piece of the material is cut out and left in the hollow part, which can be removed at the upper end of the cylinder. The mode of manufacturing such tools is very simple. A piece of square steel-bar is taken, the thick ness of which must correspond with the thickness of the handle. This is brought up to a sufficient heat in the furnace, and is then beaten or rolled laterally so as to have about the shape of a chisel. In the next stage. the edges are brought up; and finally, a man dril is put into the groove thus made, and the edges are brought together; and welded: the mandril is then withdrawn, and the tool goes to be ground and finished. It will be obvious that. by skill, punches may be made which will make holes of almost any shape. The enormous development of our iron manufactures has necessitated the use of machine-tools in the place of those made for the hand, and none of the very ingenious inventions for this purpose have played a much more important part than the punching machines. for without them the labor of drilling holes in iron plates for such objects as steam-boilers, iron-ships, bridges, and other great works, would have been so great as to have effectually prevented them from being undertaken. The punching-machine. in
vented by Messrs. Roberts and Nasmyth, with recent modifications and improvements, is in very general use in all our great engineering works; its essential parts are the punch, lever, and the spring. The punch is simply a piece of tough, hard steel of a cylindrical form, and of the size of the intended holes; it fits into a socket, which is suspended over a fixed iron plate or bench, which has a hole exactly under the punch, and exactly fitting it. In the socket which holds the punch is a coiled iron spring, which holds up the punch, and allows it to descend when the power is applied, and returns it when the pressure is relieved, The lever, when in action, presses on the top of the punch, and the plate of metal which is to be perforated being placed on the iron bench, receives the pressure of the punch with sufficient force to press out a disk of metal exactly the diameter of the punch, which falls through the hole in the iron bench. The lever is moved by a cam on a powerfull wheel, which presses upon it until it can pass; then the lever being relieved, the punch is drawn up by the spring in its socket, ready to receive the action of the cam when the revolution of the wheel again brings it to bear on the lever. The punch itself is always solid, differing entirely in this respect from the hand-tools. This useful machine will perforate thick plates of iron, such as are used for shipbuilding, almost as quickly-as a workman with an ordinary hand-punch could perforate thin plates of tin; the boles made are quite true, and are ready to receive the rivets.