After the metal has been heated it is shaped with the hammer. This shaping may consist of drawing, upsetting, or bending. In drawing a bar of iron it is made longer and of smaller diameter. Upsetting consists of shortening the bar with a corresponding increase of diameter. This work is usually done with the assistance of a helper using a sledge hammer; the smith using a light hand hammer. They strike alternate blows. The helper must watch the point upon which the smith strikes and strike in the same place. Where two helpers are employed the smith strikes after each man. A blow on the anvil by the smith is a signal to stop striking.
As the hammer usually marks the metal, it is customary to leave the metal a little full and to finish by the use of flatters and swages. This applies to work that has been shaped under the sledge. Light work can be dressed smoothly, and the hammer can be made to obliterate its own marks.
In drawing out, as well as in all other forging operations where heavy work is to be done, it is always best to heat the work to as high a temperature as the metal will stand without injury. Work can sometimes be drawn out much faster by working over the horn of the anvil than on the face, the reason being this: When a piece of work is hammered on the anvil face it flattens out and spreads nearly as much in width as it does in length, working it out longer and wider. As the piece is not wanted wider but merely longer, all the work spent in increasing the width of the stock is wasted. If the hammering is done over the horn of the anvil as illustrated in Fig. 43, the rounded horn acts as a blunt wedge, forcing the metal lengthwise and thus utilizes almost the entire energy of a blow in stretching the metal in the desired direction. Fullers are also used to serve the same purpose and when working under the steam hammer a round bar sometimes takes the place of the fuller or horn of the anvil. Round Stock. When drawing out or pointing round stock, it should always first be forged down square to the required size and then rounded up in as few blows as possible. Fig. 44 illustrates, in a general way, the different steps in drawing down a round bar from a large to a smaller size, the first step being to hammer it down square as at B. This square shape is then made octagonal as at C and the octagon is finally rounded up as at D. If an attempt be made to hammer the bar by pounding it round and round without the preliminary squaring, the bar is very liable to split through the center, the action being a good deal as illustrated in Fig. 45, the effect of the blow coming as shown by the arrows A. The metal is squeezed together in this direction and forced apart in the direction at right angles as indicated by the arrows B. Then, if the piece be slightly rolled for another blow, the sides will roll by each other, and cracks and splits will sooner or later develop, leaving the bar, if it should be sawed through the center, in a good deal the shape shown in Fig. 46. Particular care should be taken in making conical points as it is almost impossible to work stock to a round point unless the point be first forged down to a square or pyramidal shape.
Fig. 43. Method of Drawing Out Work.
Fig. 44. Drawing Down Round Bar.
Fig. 45. Wrong Method of Drawing Out.
Fig. 46. Section Showing Result of Wrong Drawing.
Fig. 47. Irregular Shapes.
Fig. 48. Method of Squaring Up Bad Corners.
In drawing out it often happens that the bar becomes worked into an irregular or diamond shape, similar to the section shown in Fig. 47. To remedy this, and square up the bad corners, the bar should be laid across the anvil and worked much as shown in Fig. 48, the blows coming in the direction indicated by the arrow. Just as the hammer strikes the work it should be given a sort of sliding motion. No attempt should be made to square up a corner by striking squarely down upon the work. The hammering should all be done in such a way as to force the metal back into the bar and away from the high corner.
When a piece is worked in such a way that its length is shortened and either or both its thickness and width increased, the piece is said to be upset and the operation is known as upsetting. There are several methods of upsetting, the one used depending largely upon the shape of the work. In short pieces the work is generally stood on end on the anvil, the hammering being done directly down upon the upper end. The work should always be kept straight, and as soon as a bend or kink is started, it should be straightened out. When a long piece is to be upset it is generally swung back and forth horizontally and the upsetting done by ramming the end against the anvil. The effect of the blow has a decided influence upon the shape of the upset piece, as shown in Fig. 49. Light blows affect the metal for a short distance only, as shown by the swelled out end; the heavier blows are felt more uniformly throughout the entire length.
When rivets are to be driven to fill holes tightly, the blows should be heavy, thus upsetting the rivet tightly into the holes. If a rivet is wanted to hold two pieces together in such a way that they may move, as for instance the rivet in a pair of tongs, the head should be formed with light blows, thus working only the end of the rivet. The part of the work which is heated to the highest temperature is the part which will be most upset, and when upsetting is wished at one point only, that point should be heated to the highest temperature, leaving the other parts of the bar as cold as possible. Upsetting long pieces is sometimes done by raising the piece and allowing it to drop on a heavy cast-iron plate set in the floor. These plates are known as upsetting plates.
Fig. 49. Upsetting Rivets.
Two kinds of punches are commonly used for making holes in hot metal; the straight hand punch used with a hand hammer, and the one used for heavier stock, provided with a handle and used with a sledge hammer. Punches should of course be made of tool steel. For punching small holes in thin iron a hand punch is ordinarily used. This is a bar of round or octagonal steel, 8 or 10 inches in length, with the end forged down tapering to the same shape, but slightly smaller than the hole to be punched. Such a punch for round holes is shown in Fig. 50. The end of the punch should be perfectly square across, not at all rounding. For heavier and faster work with a helper, a punch similar to Fig. 51 is used, the striking being done with a sledge hammer. Correct Hand Method. Fig. 52 illustrates the successive steps in punching a clean hole through a piece of hot iron. The work is first laid fiat on the anvil and the punch driven about half way through as shown at A. This compresses the metal directly underneath the end of the punch and raises a slight bulge on the opposite side of the bar. The piece is then turned over and the punch driven into the bar from this side (the hole being located by the bulge) while the bar is lying flat on the anvil. The punch should be driven about half way through, leaving the work as at C. The bar is then moved over the small round hole in the end of the anvil, or is placed on some object having a hole slightly larger than the hole to be punched, and the punch is driven clear through, forcing out the small piece A and leaving the hole as shown at D. It would seem easier to drive the punch completely through the work from one side. If this were done, however, the hole would be left as shown at E; one side would be rounded in, and the other side would be bulged out, while the hole would have a decided taper, being larger at the end from which the punching was done. If the piece is thick, a little powdered coal is put in the hole after it is started, to prevent the punch from sticking to some extent.
Fig. 50. Punch for Round Holes.
Fig. 51. Punch for Heavy and Fast Work.
Fig. 52. Stages of Punching Round Hole.