The succeeding illustration of the practice of forging will be that of the formation of a hatchet, figs. 124 and 125, which like many similar tools is made by doubling the iron around a mandrel, to form the eye of the tool: it will also permit the
* The tires of wrought-iron wheels for locomotive engines and carriages, are in general bent to the circle by somewhat analogous means to those employed in chain-making, as are likewise the skelps for the twisted barrels of guns; the latter only require a mandrel or spindle with a winch handle at the one extremity, and a loop for the end of the skelp, which is wound in contact with the mandrel by means of a fixed bar placed near the same; such barrels are coiled up in three lengths, which are joined together after the spirals are welded.
Wheels for railways display many curious examples of smithing: thus some, except the nave, are made entirely by welding; others are partly combined with rivets; in all the nave or boss is a mass of cast-iron usually poured around the ends of the spokes, with the exception of Bourne and Hartley's patent wheel, in which the nave, spokes, and periphery, are made entirely of wrought-iron and welded together.
The common practice of welding the tires of railway wheels is now as follows: the tires are cut off with ridges in the center, so as in meeting to form two angular notches into which two thin iron wedges are subsequently welded radially; the four parts thus united together in the form of a cross, make a very secure joint without the necessity for upsetting the iron, which would distort the form of the tire description of some other general proceedings, and likewise the introduction of the steel for the cutting edge.
In making the hatchet, a piece of flat iron is selected of the width of A E, and twice the length of AD; it is thinned and extended sideways before it is folded together, to form the projections near B and F, by blows with the pane of the hammer or a round-edged fuller, on the lines A B to E F, but the metal must be preserved of the full thickness at the part A E, to form the poll of the hatchet, although a piece of steel is frequently welded on at that part as a previous step. The work is then bent round a mandrel, figs. 126 and 127, exactly of the section of the eye as seen in fig. 125, and the work is welded across the line B F; the mandrel is again introduced, and the eye is perfected.
A slip of shear-steel, equal in length to D H, is next inserted between the two tails of the iron, as yet of their original size, up to the former weld, and all three are welded together between C, G, D, H: the combined iron and steel are now drawn out sideways, by blows of the pane of the hammer on and between C D and G H, to extend them together to I J. The tool is then flattened and smoothed with the face of the hammer, and the edges are pared with straight or circular chisels to the particular pattern, and trimmed with a round-faced hammer, or a top fuller.
In smoothing off the work, the smith pursues his common method of first removing with a file the hard black scales that appear like spots when the work is removed from the fire; he then dips the hammer in the slake trough, and lets fall upon the anvil a few drops of the water it picks up, the explosion of which when the red-hot metal is struck upon it, makes a smart report and detaches the scales that would be other wise indented in the work. It should be observed that the mandrel, fig. 126, is purposely made very taper, and is introduced into the hole from both sides, so that the eye may be smaller in the middle: when therefore the handle of the tool is carefully fitted and wedged in, the handle is as it were dove-tailed, and the tool can neither fly off nor slip down the handle; the same mode is also adopted for the heads of hammers.
In spades, and many similar implements, the steel is introduced between the two pieces of iron of which the tools are made; in others, as plane irons and socket chisels, it is laid on the outside, and the two are afterwards extended in length or width to the required size. The ordinary chisel for the smith's shop is made by inserting the steel in a cleft, as in fig. 118, page 220, and so is also the pane of a hammer; but the flat face of the hammer is sometimes stuck on whilst it continues at the extremity of a flat bar of steel; it is then cut off, and the welding is afterwards completed. At other times the face of the hammer is prepared like a nail, with a small spike and a very large head, so as to be driven into the iron to retain its position, until finally secured by the operation of welding.
In putting a piece of steel into the end of an iron rod to serve for a center, the bar is heated, fixed horizontally in the vice, and punched lengthways with a sharp square punch, for the reception of the steel, which is drawn down like a taper tang or thick nail, and driven in; the whole is then returned to the fire, and when at the proper heat united by welding, the blows being first directed as for forming a very obtuse cone to prevent the piece of steel from dropping out.
For some few purposes the blistered steel is used for welding, either itself or to iron; it is true the first working under the hammer in a measure changes it to the condition of shear-steel, but less efficiently so than when the ordinary course of manu-facture is panned, as the hammering is found to improve steel in a remarkable and increasing degree. For the majority of works in which it is necessary to weld steel to iron, or steel to steel, the shear, or double shear, is ex-ceedingly suitable; it is used for welding upon various cutting tools, as the majority of the cast-steel will not endure the heat without crumbling under the hammer. Shear-steel is also used for various kinds of springs, and for some cutting tools requiring much elasticity.
It is more usual to reserve the cast-steel for those works in which the process of welding is not required, although of late years mild cast-steel, or welding cast-steel, containing a smaller proportion of carbon has been rather extensively used; but in general the harder the steel the less easily will it admit of welding, and not unfrequently it is altogether inadmissible.
The hard or harsh varieties of cast-steel, are somewhat more manageable when fused borax is used as a defence instead of sand, either sprinkled on in powder or rubbed on in a lump: and cast-steel otherwise intractable may be sometimes welded to iron by first heating the iron pretty smartly, then placing the cold steel beside it in the fire, and welding them the moment the steel has acquired its maximum temperature, by which time the iron will be fully up to the welding heat. When both are put into the fire cold alike, the steel is often spoiled before the iron is nearly hot enough, and therefore it is generally usual to heat the iron and steel separately, and only to place them in contact towards the conclusion of the period of getting up the heat. In forging works either of iron or steel, the uniformity of the hammering tends greatly to increase and equalize the strength of each material: and in steel, judicious and equal forging greatly lessens also the after-risk in hardening.*