It is easy to see how a difference in relative proportions would modify the method of making which ought to be adopted, and since our connecting rod is selected, not as of any particular size, but illustrative only of different methods of forging, we will now make it the medium of sundry remarks in reference to the practice of welding.
Upsetting is hard work when the quantity of metal to be upset is large, and particularly so when done without the aid of a monkey, or in the absence of a massive plate which is frequently sunk in the floor for the same purpose. Welding is, therefore, much easier in certain instances. But the stub end B (Fig. 245) is not so much larger than the original size of the bar in the centre; therefore we may upset that very well. Also, when the sum of the widths of the two forks is little more than that of the original bar, and the forks are forged as in the last example, we may accept the jumping up method as being practicable. Moreover, in the first instance described, we upset the bar on the supposition that, though the end was solid, it was not of great width, and this would also be applicable to the ends of many light levers. But assuming the end were both solid and wide, measuring, say, over the bosses 3 or 4 times the diameter of the bar in the centre, welding then would be preferable because involving less labour.
When making a weld, there are three points to be borne in mind: to have a joint of sufficient area, and in suitable direction for hammering up; to have the necessary temperature; and to be sure of perfectly clean surfaces. For the first condition, a scarf joint, that is, one running diagonally with the common axis of the pieces to be shut (Fig. 251), is to be preferred, and is, therefore, commonly employed when practicable. When a scarf joint cannot be used, a veed or cleft joint is suitable. When that cannot be employed, a spreading joint, made by fullering down a portion of the bar, is resorted to. A plain butt joint, except when the abutting surfaces are of large area, is seldom used; but flat surface shuts are common. The temperature for welding iron is that just now referred to, when the iron begins to sparkle, and to drop off in globules. For steel, the temperature is lower, barely approaching to a white heat. Different qualities of iron and steel require different degrees of heat, and the temperature in each case become a matter of experience. When the ends to be welded are taken from the fire, any scale adherent to the surface must be detached by striking the bar smartly on the anvil, joint face downward, or by sweeping away the scale with a muck brush.
If any • persistently adhering scale remains on the faces, the shut should not be made.
Fractures occur sometimes from this reason, the weld being perfect near the edges, but faulty in the centre. The joint surfaces are usually dusted with sand, but this is not so essential as it is sometimes stated to be, provided the scale is removed in the manner stated, for numbers of ordinary iron shuts are made without it. The weld is made immediately that the faces are brought into contact, by rapid hammering, every second at the welding heat being of vita? importance. When closed together with the hammer, the joint of a good weld should not be visible, the presence of a black line indicating that the shut is imperfect. If during ham mering the bar becomes reduced or drawn down below its proper size, diameter, width, or thickness, as the case may be, it must be slightly jumped up to thicken it sufficiently, and then swaged circular, or smoothed with the flatter. Iron and iron are easily welded, so are the milder varieties of steel; but some hard and brittle steels require tact and practice to weld properly, and some, if heated over a certain temperature, crumble under the hammer.
In a connecting rod, the cotter way in the stub end is usually drilled and filed out, but in many instances cotter ways and holes of other shapes are punched and drifted, either to save the labour of drilling previous to filing through, or as being suitable enough for the purpose which they have to fulfil. Before punching, the iron is brought to a welding heat, or nearly so, laid upon the anvil, and the punch, struck with the hammer, is made to pass half way through from one face. It is then knocked back, the iron turned over and punched from the opposite face, the holes meeting, therefore, in the middle or thereabout. Then a drift is inserted i*i the hole, and either driven half way in from each side, or right through, according to circumstances. While the drift is still in place, opportunity is taken of giving a rough kind of finish to the exterior outline. Punches and drifts become red hot, and soften and bend if they remain more than a few minutes in contact with the iron, so that it is necessary to remove them once or twice from a deep hole and quench them in water. Punches and drifts are usually picked up with the pliers, though the former are sometimes finished with withy handles.
They are circular, oval, or rectangular in section, the difference being that while a punch is tapered, a drift is parallel for a considerable portion of its length, and tapers only toward the end.
When bending work, various devices are resorted to. A turn-down edge at right angles would be bent over the edge of the anvil, the flat of the bar lying horizontally across the anvil, the smith grasping the tongs, and steadying them against his leg to resist the force of the endlong blows. The bar is frequently nicked across slightly with a fuller previous to bending, and the fuller, having a circular section, does not divide the fibre as a set would do. Eyes or rings are bent around the beak of the anvil, whose tapered outline permits. eyes, rings, loops, and curves of many different diameters being bent. Fig. 252 shows the method of welding a ring and an eye. Rings of large diameter are finished on the conical mandrel (Fig. 253). Small rings are finished on a parallel bar or mandrel of suitable diameter, the bar remaining in place while the outside is finished with flatters or swages. When eyes are being bent, or other work being performed on bars of considerable length, the trouble of supporting the opposite end is saved by driving a rest (Fig. 254) into the ground, and placing the bar in the hollow.