The black-red heat, just visible by daylight; The low-red heat; The bright-red heat, when the black scales may be seen; The welding-heat, when the iron begins to burn with vivid sparks. Steel requires on the whole very much more precaution as to the degree of heat, than iron. The temperature of cast steel should not generally exceed a bright-red heat; that of blistered and shear-steel that of a moderate white-heat. Although steel cannot in consequence be so far softened in the fire as iron, and is therefore always more dense and harder to forge; still from its superior cohesion it bears a much greater amount of hard work under the hammer when it is not over-heated or burned; but the smallest available temperature should be always employed with this material, as in fact with all others. It has been recommended to try by experiment the lowest degree of heat at which every sample of steel will harden, and in forging always to keep a trifle below that point. This proposal however is rarely tried, and still less followed, as the usual attempt is to lessen the labor of forging by softening the steel so far as it is safely practicable. 1 Iron is more commonly worked at the bright-red and the whiteheats, the welding-heat being reserved for those cases in which welding is required; or others in which, from the great extension or working of the iron, there is risk of separating its fibres or laminæ, so as to cause the work to become unsound or hollow from the disrupture of its substance; whereas the same processes being carried on at the welding temperature, the work would be kept sound, as every blow would effect the operation of welding rather than that of separation. The cracks and defects in iron are generally very plainly shown by a difference in color at the parts when they are heated to a dull-red. This method of trial is often had recourse to in examining the soundness both of new and old forgings. When a piece of forged work is required to be particularly sound, it is a common practice to subject every part of the material in succession to a welding heat, and to work it well under the hammer, as a repetition of the process of manufacture to insure the perfection of the iron; this is technically called taking a heat over it-in fact, a heat is generally understood to imply the welding heat. For a two-inch shaft of the soundest quality, two and a half inch iron would be selected, to allow for the reduction in the fire and the lathe. Some also twist the iron before the hammering to prevent it from becoming "spilly." The use of sand sprinkled upon the iron is to preserve it from absolute contact with the air, which would cause it to waste away from the oxidation of its surface, and fall off in scales around the anvil. If the sand is thrown on when the metal is only at the full red heat it falls off without adhering; but, when the white heat is approached, the sand begins to adhere to the iron; it next melts on its surface, over which it then runs like fluid glass, and defends it from the air. When this point has been rather exceeded, so that the metal nevertheless begins to burn with vivid sparks and a hissing noise like fireworks, the welding temperature is arrived at, and which should not be exceeded. The sparks are, however, considered a sign of a dirty fire or bad iron, as the purer the iron the less it is subject to waste or oxidation, in the course of work. In welding two pieces of iron together, care must be taken that both arrive at the welding heat at the same moment; it may be necessary to keep one of the pieces a little on one side of the most intense part of the fire (which is just opposite the blast), should the one be in advance of the other. In all cases, a certain amount of time is essential, otherwise, if the fire be unnecessarily urged, the outer case of the iron may be at the point of ignition before the centre has exceeded the red heat. In welding iron to steel, the latter must be heated in a considerably less degree than the iron, the welding heat of steel being lower from its greater fusibility. But the process of welding will be separately considered under a few of its most general applications, when the ordinary practice of forging has been discussed, and to which we will now proceed. ORDINARY PRACTICE OF FORGING. THE general practices of forging works from the bar of iron or steel are, for the most part, included in the three following modes: the first two occur in almost every case, and frequently all three together, namely: By drawing-down, or reduction; By jumping, or up-setting; otherwise, thickening and shortening; By building-up, or welding. When it is desired to reduce the general thickness of the object, both in length and width, then the flat face of the hammer is made to fall level upon the work; but, where the length or breadth alone is to be extended, the pane or narrow edge of the hammer is first used, and its blows are directed at the right angles to the direction in which the iron is to be spread. To meet the variety of cases which occur, the smith has hammers in which the panes are made in different ways-either at right angles to the handle, parallel with the same, or oblique. In order to obtain the same results with more precision and effect, tools of the same characters, but which are struck with the sledge-hammer, are also commonly used. Those with flat faces are made like hammers, and usually with similar handles, except that, for the convenience of reversing them, they are not wedged in; these are called set-hammers; others, which have very broad faces, are called flatters; and the top tools, with narrow round edges like the pane of the hammer, are called top-fullers. They all have the ordinary hazel rods. When the sides of the object are required to be parallel, and it is to be reduced both in width and thickness, the flat face of the hammer is made to fall parallel with the anvil, as represented in Fig. 43, or oblique, for producing taper pieces, as in Fig. 44, and. action and reaction being equal, the lower face of the work receives the same absolute blow from the anvil as that applied above by the hammer itself. It is not requisite, therefore, to present every one of the four sides to the hammer, but any two at right angles to each other. This is only true for works of moderate dimensions; in large masses, such as anchors, the soft doughy state of the metal acts as a cushion, and greatly lessens the recoil of the anvil, and on this account such works are presented to the hammer on all four sides. It is also very injudicious in such cases to continue the exterior finish, or battering-off, too long, as this extends the outer case of the metal more than the inner part, and sometimes separates the two. When imperfect forgings are broken in the act of being proved, the inner bars are sometimes found not to be even welded together, and the outside part is a detached sheath, almost like the rind or bark of a tree. In twisting the work round the quarter circle, some practice is called for, in order to retain the rectangular section, and not to allow it to degenerate into the lozenge or rhomboidal form, which error it is difficult to retrace. This indeed may be considered the first stumbling block in forging, and one for which it is difficult to provide written rules. Of course in converting a round bar into a square with_the_hammer, the accuracy will depend almost entirely upon the change of exactly ninety degrees being given to the work, and this the experienced smith will accomplish with that same degree of feeling, or intuition, which teaches the exact distances required upon the finger-board of a violin, which is defined by habit alone. In the original manufacture of the iron, the carefully turned grooves, a, b, c, of the rollers, page 81, produce the square figure with great truth and facility; and under the tilt-hammer the two opposite sides are sure to be parallel, from the respective parallelism of the faces of the hammer and anvil; and the tietrs, from constant practice, apply the work with great truth in its second position. So that under ordinary circumstances the prepared materials are true and square, and the smith has principally to avoid losing that accuracy. First, he must acquire the habit of feeling when the bar lies perfectly flat upon the anvil, by holding it slenderly, leaving it almost to rotate in his grasp, or in fact to place itself. Next, he must cause the hammer to fall flat upon the work: with which view he will neither grasp its handle close against the head of the hammer, nor at the extreme end of the handle, but at that intermediate point where he finds it comfortably to rebound from the anvil, with the least effort of, or jar to his wrist. And the height of the wrist must also be such as not to allow either the front or back edge of the hammer-face to strike the work first, which would indent it, but it must fall fair and parallel, and without bruising the work. It would be desirable practice to hammer a bar of cold iron, cr still better one of steel, as there would be more leisure for observation, the indentations of the hammer could be easily noticed; and if the work, especially steel, were held too tightly, or without resting fairly on the anvil, it would indicate the error by additional noise and by jarring the wrist; whereas, when hot, the false blows or positions would cause the work to get out of shape, without such indications. As to the best form of the hammer, there is much of habit and something of fancy. The ordinary hand-hammer is represented in Figs. 43 and 44, but most tool makers prefer the hammer without a pane, and with the handle quite at the top, the two forming almost a right angle, or from that to about eighty degrees; and sometimes the head is bent like a portion of a circle. Similar but much heavier hand-hammers, occasionally of the weight of twelve or fourteen pounds, are used by the spade-makers for planishing; but the work being thin and cold, the hammer rises almost exclusively by the reaction, and requires little more than guidance. Again, the farriers prefer for some parts of their work, a hammer the head of which is almost a sphere; it has two flat faces, one rounded face for the inside of the shoe, and one very stunted pane at right angles to the handle, used for drawing down the clip in front of the horse-shoe; in fact, nearly a small volume might be written upon all the varieties of hammers. To return to the forging: the flat face of the hammer should not only fall flat, but also centrally upon the work; that is, the centre of the hammer, in which point the principal force of the blow is concentrated, should fall on the centre of the bar otherwise that edge of the work to which the hammer might lean would be the more reduced, and consequently the parallelism of the work would be lost. It would also be bent in respect to length, as the thinned edge would become more elongated, and thence convex; and when the blows were irregularly scattered, the work would become twisted or put in winding, which would be a still worse error. I will suppose it required to draw down (the technical term for reduction), six inches of the end of a square or rectangular bar of iron or steel; the smith will place the bar across the anvil with perhaps four inches overhanging, and not resting quite flat, but tilted up about a quarter or half an inch at the near side of the anvil, as in Fig. 44, but less in degree, and the hammer will be made to fall as there shown, except that it will be at a very small angle with the anvil. Having given one blow, he will as the only change, twist the work a quarter turn, and strike it again; then he will draw the bar half an inch or an inch towards him, and give it two more similar blows, and so on until he arrives at the extreme end, when he will recommence; but this will be done almost in the time of reading these words. The descent of the hammer, the drawing the work towards himself (whence perhaps the term), and the quarter turn backwards and forwards, all go on simultaneously and with some expedition. At other times the work is drawn down over the beak iron, in which case the curvature of this part of the anvil makes it less material at what angle the work is held or the blows given, provided the two positions be alike. In smoothing off the work, the position of Fig. 43 is assumed; the work is laid flat upon the anvil, and the hammer is made to fall as nearly as possible horizontally; a series of blows are given all along the work between every quarter turn, the hammer being directed upon one spot, and the work drawn gradually be neath it. The circumstances are exactly the same as regards the sledgehammer, which is used up-hand for light work; the right hand being slid towards the head in the act of lifting the hammer from off the work, and slipped down again as the tool descends; and the conditions are scarcely altered when the smith swings the hammer about in a circle, the signal for which is "about sledge;" whereas when, in either case, the blows of the sledge hammer are to be discontinued, the fireman taps the anvil with his hand-hammer, which is, I believe, an universal language. In drawing down the tang or taper-point of a tool, the extreme end of the iron or steel is placed a little beyond the edge of the anvil, as in Fig. 44 by which means the risk of indenting the anvil is entirely removed, and the small irregular piece in excess beyond the taper is not cut off until the tang is completed. Fig. 45 shows the position of the chisel in cutting off the finished object from the bar of which it formed a part; that is, the work is placed betwixt the edge of the anvil, and that of the chisel immediately above the same; the two resemble in effect a pair of shears Sometimes the edge of the anvil alone is used for small objects, |