Beginning this section with the tools having the most acute edges, we have to refer to the punch pliers, fig. 947, fitted with round hollow punches for making holes in leather straps and thin materials; some pliers of this kind have a small oval punch terminating in a chisel edge, for cutting those holes that have to be passed over buttons; and pliers have been made with circular, square, and triangular punches, for the cruel practice of marking sheep in the ear. In all these tools the punch is made to close upon a small block of ivory or copper, so as to ensure the material being cut through without injuring the punch.
Another example of slender thisel-like punches, is to be seen in Mr. Roger's machine for cutting the teeth of horn and tor-toiseshell combs (see page 130, vol. i.). The punch or chisel is in two parts, slightly inclined and curved at the ends to agree in form with the outline of one tooth of the comb, the cutter is attached to the end of a jointed arm, moved up and down by a crank, so as to penetrate almost through the material, and the uncut portion is so very thin that it splits through at each stroke, and leaves the two combs detached.
The little instrument called a pen-making machine, is another ingenious example of punches moving on a joint, it is represented of half its true size, and ready to receive the pen, in fig. 948, and in fig. 949, the two cutters are shown of full size and laid back in a right line; although in reality it only opens to a right angle. The lower half has a small steel cutter b, pointed to the angle of the nibs of the pen, and fluted to the curve of the quill as at a, the upper cutter d, is made as an inverted angle with nearly vertical edges as seen at e, which exactly correspond with the lower cutter, so as between them to cut the shoulders of the pen. The upper tool also carries a thin blade or chisel, which penetrates nearly through the quill and forms the slit.
The quill having been pared down to its central line, is inserted through the hollow joint, on the line /, and the cutters being very near the joint, the lever on being closed gives abundant power for the penetration of the punches. The pen requires to be afterwards nibbed, and for which purpose another cutter is attached to the instrument which has likewise an ordinary pen-blade, so as to be entirely complete in itself.
This method of producing a pen was introduced in a somewhat different form, in the late Mr. Timothy Bramah's patent machinery for making portable quill pens, the barrel of the quill was in that case cut into two lengths, and each length being split longitudinally into three parts, and shaped at each end in a small fly-press with cutters of the above character, converted every quill into six double-ended pens, many thousand boxes of which were made; they may be considered to have opened the path to the present truly enormous manufacture of steel pens, which consumes many tons of steel annually.
Passing from the punches with guides obtained by means of joints, and actuated by the pressure of the fingers, we will return to fig. 94-5, on page 929, which with its simple guide becomes a very effective tool sometimes known as the hammer press, in contradistinction to the screw or fly press to be hereafter spoken of.
The guide in the contrivance fig. 945, is a strong piece of iron attached to the bottom tool, and sufficiently above it to admit the work between the two. Each part is pierced with a hole of exactly the same size, and accurately formed as if they were interrupted portions of the same hole. The punch is made exactly to fit either hole, so that from the upper it receives a correct guidance, and it therefore cuts through the material, and penetrates the lower piece, with a degree of precision and truth scarcely attainable when the tools are unattached, and are used simply upon the anvil as before described.
As however the punch mostly sticks tight in the work, it is needful to turn the instrument over, and drive out the punch with a drift a little smaller than the punch, and on which account punching tools of this kind are often made of two parallel plates of steel firmly united by screws or steady pins, yet separated enough for the reception of the work, and frequently contrivances are added to guide the works to one fixed position, in order that any number of pieces may be punched exactly alike.
Thus in punching circular mortises, as in the half of a pair of inside and outside callipers a, fig. 950, the punch c, is first used to produce the central hole, and this punch is then left in the bed b, to retain the work during the action of the second punch to, by which the mortise is cut. The punch to, is very short to avoid the chance of its being broken, and it is also narrow so as to embrace only a short portion of the mortise, which is then completed, with little risk to the tool, at three or four strokes, whilst the punch c serves as a central guide.
Occasionally also punches of this simple kind, but on a larger scale, have been placed under drop hammers, falling from a considerable height through guide rods, somewhat as in a pile-driving machine. This mode of obtaining power is not suited to the action of punches used in cutting out metals, amongst other reasons, because the punch sticks very hard in the perforation it has made, and requires some contrivance for pulling it out, which is not so easily obtained in this apparatus as in fly presses, that are suited alike to large and small works.
The drop hammer, or as it is more commonly called a force, is, however, very much used at Birmingham in the manufacture of stamped work, or such as are figured between dies, of which an example is described at length in pages 409 & 410 of vol. i. Compared with a fly-press of equal power, the force is less expensive in its first construction, but it is also less accurate in its performance.
Fig. 951 is a very simple yet effective tool which may be viewed as a simplification of the fly-press, it consists of one very strong piece of wrought iron, about one inch thick and four or five inches wide, thickened at the ends and bent into the form represented, the one extremity is tapped to receive a coarse screw, the end of which is formed as a cylindrical pin, or punch, that is sometimes made in the solid with the screw, but more usually as a hardened steel plug inserted in a hole in the screw. Immediately opposite to the punch is another hole in the press, the extremity of which is fitted with a hardened steel ring or bed punch. When the screw is turned round by a lever about three feet long, it will make holes as large as 3/4 inch diameter in plates 3/4 inch thick, and is therefore occasionally useful to boiler-makers for repairs, and also for fitting works in confined situations about the holds of ships, and other purposes. When this screw is turned backwards the punch is drawn out and relieved from the work, but the screwing motion is apt to wear out the end and side of the punch, and therefore to alter its dimensions.
A very convenient instrument of exactly the same kind is used in punching the holes in leather straps, by which they are laced together with leather thongs, or united by screws and nuts, to constitute the endless bauds or belts used in driving machinery. In this case the frame of the tool is made of gun-metal, and weighs only a few ounces, the end of the screw is formed as a cutting punch, and it is perforated throughout, that the little cylinders of leather may work out through the screw, which only requires a cross handle to adapt it to the thumb and fingers.
In this case the screwing motion is desirable, as the punch in revolving acts partly as a knife, and therefore cuts with great facility, as the leather is supported by the gun-metal which constitutes the clamp or body of the tool.