Modern Machine-Shop Practice Part 192

The proper shape for blacksmiths' tongs depends upon whether they are to be used upon work of a uniform size and shape, or upon general work. In the first case, the tongs may be formed to exactly suit the special work. In the second case, they must be formed to suit as wide a range of work as convenient.

Suppose, for example, the tongs are for use on a special size and shape of metal only; then they should be formed so that the jaws will grip the work evenly all along, and therefore be straight along the gripping surface. It will be readily perceived, however, that if such tongs were put upon a piece of work of greater thickness, they would grip it at the inner end only, and it would be impossible to hold the work steady. The end of the work would act as a pivot, and the part on the anvil would move about. It is better, therefore, for general work to curve the jaws, putting the work sufficiently within the jaws to meet them at the back of the jaw, when the end will also grip the work. By putting the work more or less within the tongs, according to its thickness, contact at the end of the work and at the point of the tongs may be secured in one pair of tongs over a wider range of thickness of work than would otherwise be the case. This applies to tongs for round or other work equally as well as to flat or square work.

To maintain the jaw pressure of the tongs upon the work, a ring is employed, the tong ends being curved to prevent the ring from slipping off.

After a piece of work has left the fire it should, if there are scales adhering upon it, have them cleaned off before being forged, for which purpose the hammer head or an old file is used, otherwise the forging will not be smooth, and the scale will be hammered into the surface.

This will render the forging very hard to operate upon by steel cutting tools, and cause them to dull rapidly. For the same reason it is proper to heat a finished forging to a low red heat and pa.s.s a file over its surface, which will leave the forging soft as well as free from scale. A forging should not be finally finished by being swaged or forged after it has become black hot, because it produces a surface tension that throws the work out of true as the metal is cut away in finishing it.

Work to be drawn out is treated according to the amount of elongation and reduction of diameter required. Thus, suppose a piece of square work to require to be drawn out, then it is hammered on its respective sides, being turned upon the anvil so that each successive side shall receive the hammer blows. It is essential, however, that the piece be forged square, or in other words, that during the forging the sides be kept at a right angle one to the other, or else the work will hammer hollow, as it is termed; that is to say, the iron will split at the centre of the bar, which occurs from its being forged diamond-shaped instead of square. If a piece required to be forged diamond-shaped, it must be forged square until reduced to such dimensions as will leave sufficient to draw out while altering its form from the square to the diamond-shape.

In very small work, which is more apt to hammer hollow than large work, the end of the piece is left of enlarged size, as shown in the figure, the strength of the enlarged end serving to prevent the hammering hollow, which usually begins at the end of the piece; the end is in this case forged last. In the case of round work the same rule holds good, inasmuch as that a round bar may be forged smaller to some extent, either by hammer blows or by swaging, but if the forging by hammer blows be excessive, hammering hollow is liable to ensue.

The blacksmith's set of chisels consists of a hot chisel for cutting off hot iron, a cold chisel for cutting cold metal, a hardy, which sets in the square hole in the anvil, [C]-chisels, which are curved somewhat like the carpenter's gouge, and a cornering or [V]-chisel, in which the cutting edges are at a right angle one to the other.

[Ill.u.s.tration: Fig. 2844.]

The hot chisel has its edge well curved in its length, and is kept cool by lifting it from the work after each hammer blow, and by occasionally dipping it in water. Lifting it also prevents it from wedging in the work. The cold chisel is tempered to a blue, and answers virtually to the machinist's chisel. The hardy is used for small work, which is laid upon it and struck with the hammer. The [C]-chisel is used, not only in curved corners, but also to cut off deep cuts, answering, like the cape or cross-cut chisel of the machinist, to relieve the corners of the hot chisel. The cornering chisel is used for square corners, situated so that the hot chisel cannot be used. The blacksmith's punch is made well taper, so that it shall not wedge in the hole it produces.

For large holes a small punch is first used, and the hole enlarged in diameter by driving in punches of larger diameter. If this swells the work at the sides, it is forged down while the punch is in the hole.

The first blow given to the punch is a light one, so as to leave an indentation that will mark the location, and enable its easy correction if necessary. The blows delivered after the correct location is indented are quick and heavy; but a piece of soft coal is inserted and the punch placed on top of it, the gases formed by the combustion of the coal serving to prevent the punch from binding in the hole. Between the blows the blacksmith lifts the punch and moves the handle part of a lateral rotation, which prevents it from becoming fast in the hole. The punch should not be suffered to get red hot, but must be removed and cooled, a fresh piece of green soft coal being inserted in the hole just previous to the punch. If the punch is allowed to become as heated as the work, the end will "upset" or swell and become firmly locked. Should the punch lock in the hole a few blows will usually loosen it, but in extreme cases it is sometimes necessary to employ another punch from the opposite side of the work. Unless in very thin work, the hole is punched half way from each side, because by that means a short stout punch may be used.

It is obvious that when the hole requires to be bell-mouthed or of any other form, the punch must be made to correspond.

The tools employed by the blacksmith, other than tongs, hammers, chisels, and punches, are composed mainly of "fullers" and "swages" of various kinds. The fuller is essentially a spreading tool, while the swage may be termed essentially a shaping one.

[Ill.u.s.tration: Fig. 2845.]

In Fig. 2845, for example, let A represent an end view of an anvil, B the bottom, and C the top fuller, and the effects of blows upon C will be mainly to stretch the piece in the direction of its length without swelling it out sideways.

[Ill.u.s.tration: Fig. 2846.]

[Ill.u.s.tration: Fig. 2847.]

[Ill.u.s.tration: Fig. 2848.]

[Ill.u.s.tration: Fig. 2849.]

If the work requires to be swelled sideways we turn the fuller the other way around, as in Fig. 2846, in which it is supposed that one side of the work is to be kept flat, hence no bottom fuller is employed. The action of a fuller may be increased in the required direction by leaning in the direction in which we desire to drive the iron; thus, suppose we require to spread the end of a rectangular bar from the full lines to the dotted ones in Fig. 2847 and the first fuller across the piece as at A, Fig. 2848, and then spread out the end by fullering, as in Fig. 2849, inclining the fuller in the direction in which we desire to forge the iron.

[Ill.u.s.tration: Fig. 2850.]

It is the roundness of the face of the fuller that serves to control the direction in which it will drive the iron, since the curve acts somewhat on the principle of a wedge. Suppose, for example, that the faces were flat, as in Fig. 2850, and the iron would spread in both directions, the same as though the hammer were used direct, and if the work were intended to be kept parallel it would frequently require to be turned on edge to forge down the bulge that would form on the edge.

[Ill.u.s.tration: Fig. 2851.]

Fullers are, however, also used as finishing tools for curves or corners, an example being given in Fig. 2851, which represents a fuller applied to finish the round corner of a collar.

[Ill.u.s.tration: Fig. 2852.]

[Ill.u.s.tration: Fig. 2853.]

[Ill.u.s.tration: Fig. 2854.]

For finishing plane surfaces the flatter shown in Fig. 2852 is employed, W representing the work. For inside surfaces the flatter requires to be offset, as in Fig. 2853, in which L represents a link whose face A may be flattened by the flatter F. There is a tendency in this case for the flatter to tip or cant; and to avoid this and regulate the flatter upon the work, a side foot is sometimes added, as at A in Fig. 2854.

Swages are shaped according to the kind of work they are to be used for.

[Ill.u.s.tration: Fig. 2855.]

[Ill.u.s.tration: Fig. 2856.]

Fig. 2855, for example, represents a top and bottom swage for rounding up iron. For general work the recesses or seats of such swages would be made considerably oval, as in Fig. 2856, the work being revolved slightly after each blow. This capacitates one swage for different sizes of iron. When, however, a swage is to be used for one particular size only, its cavity may be made more nearly a true half circle and may envelop one half the diameter of the work, so that when the top and bottom swages meet, the work will be known to be of the required diameter without measuring it. If the seat were made a true half circle it would lock upon the work, preventing the smith from revolving it and making it difficult to remove the swage.

[Ill.u.s.tration: Fig. 2857.]

If the conditions are such that a swage must be used to perform forging rather than finishing, its seat should be [V]-shaped and not curved.

Suppose, for example, that a piece of iron, say, 6 inches in diameter, required a short section to be forged down to a diameter of 3 inches, then the swages should be formed as in Fig. 2857, because otherwise the effects of the blow will act to a certain extent to force the iron out sideways, for reasons which will be explained presently.

[Ill.u.s.tration: Fig. 2858.]

[Ill.u.s.tration: Fig. 2859.]

[Ill.u.s.tration: Fig. 2860.]

In some cases, for small work, the upper swage is guided by the lower one: thus, in Fig. 2858 is a swage for a cross piece, and the outside of its base is squared and fits easily within the upper part of the lower one shown in Fig. 2859. For very small work, on which the hand hammer is sufficiently heavy to perform the swaging, a spring swage may be use: thus, in Fig. 2860 is a swage for pieces of 3/8, 5/16, and 1/4 inch in diameter, and having a square stem fitting into the square hole in the anvil. Fig. 2861 represents a spring swage for a pin having a collar, and it may be observed that the recess to form the collar must be tapered narrowest at the bottom, so that the top swage will readily release itself by the force of the spring, and so that the work may easily be revolved in the lower one. A similar tool is shown in Fig.

2862, designed for punching sheet metal cold, the die D being changeable for different sizes of punches P.

[Ill.u.s.tration: Fig. 2861.]

[Ill.u.s.tration: Fig. 2862.]

[Ill.u.s.tration: Fig. 2863.]

For large hand-made forgings the swage block, such as in Fig. 2863, is employed, S representing a stand for the block, whose dimensions are larger than the block, so that the latter may be rested on its face in the stand when the holes are to be used.

[Ill.u.s.tration: Fig. 2864.]

Fig. 2864 represents a swage block mounted on bearers, so that it may be revolved to bring the necessary cavity uppermost.

[Ill.u.s.tration: Fig. 2865.]

[Ill.u.s.tration: Fig. 2866.]

[Ill.u.s.tration: Fig. 2867.]

Swages for trip hammers or for small steam hammers are for work not exceeding about 4 inches in diameter, made as in Fig. 2865, the weight of the top swage being sufficient to keep the two closed as in the figure; for larger sizes the bottom swage fits to the anvil, and the top one is provided with a handle, as in Fig. 2866, B representing the anvil block, S' the bottom, and S the top swage, having a handle H. The f.l.a.n.g.e of the bottom swage is placed as in Fig. 2867, so as to prevent the swage from moving off the anvil block when the work is pushed through it endways. Obviously such swages are employed when the part to be swaged is less in length than the width of the hammer or of the anvil face.