The forging of a two-piston-rod crosshead is performed by several methods, the plan selected depending upon the resources of the maker. A convenient mode to avoid bending consists in making it of three pieces. The thickest or mid-portion of the crosshead is made of one piece; and the other two constitute the two ends for the piston-rods. These three portions are shown in Fig. 163.

To make the middle part, a lump is selected whose sectional area is rather greater than that of the largest part of the intended piece. A porter is attached to one end, and the circular part is shaped to its intended form. The length of this part is next marked by a chisel being driven in at two places, and the work is reduced from the larger mid-portion to form the two square or four-sided ends.

The two ends or stems thus produced, are next prepared for a tongue-joint, by making a gap in each end, to which the other two pieces will be welded ; and, by allowing thick lumps to remain at the ends during the drawing down of the stems, upsetting for the joint will be avoided.

The other two pieces are next prepared, or may have been in progress at another furnace during the forging of the middle part. Straight pieces are used for these two parts, with porters attached, as for the middle part. After the bosses of these two pieces are formed, the projecting stems are cut to a proper length and shaped to fit the openings in the stems of the middle piece, and when the suitable length to admit a stretching after welding is attained, the three are welded together.

After being welded together, the four-sided parts, or arms, of the work are drawn until the proper distances between the centre of the crosshead and the centres of the intended holes are attained. The superfluous iron that then remains must be either cut off with chisels or allowed to remain for planing and shaping. During the hammering for welding, and also during the trimming with chisels, two protuberances should be allowed to remain for centring purposes. In these projections the recesses are made, by means of which the circular portion in the middle is turned. These centre-pieces are shown in Fig. 112 by dots and the two letters C C.

Two piston-rod crossheads are made also of one piece; the troublesome joint-making being thereby avoided.

By this mode a lump of rather greater sectional area than the middle of the crosshead is made use of; and the length of the iron required for one of the four-sided ends is ascertained with proper measurement, and by the rule. This length is marked upon one end of the piece, at a proper distance from the extremity ; fullers are next driven in, and the work reduced on both sides of the intended mid-portion ; or, for portability, the entire length necessary for the crosshead may be cut from the lump, if it is desirable to handle only the smallest quantity of metal that is sufficient. During the drawing down, a lump is allowed to remain at each end of the work, which is amply sufficient for the circular boss that is to contain the end of the piston-rod. Two small projections also, are allowed to remain for the centre-pieces, C C.

When the work is lengthened nearly to its intended length, the bending or curving is accomplished.

A short length of the four-sided part on both sides of the circular portion is in line with its centre, so that it is necessary to prevent these two parts being bent or put out of position during the angling or bending of the adjoining ends. Consequently, whether the work is to be angled or curved, as in the Figure (112), the iron, after being heated to nearly welding, is cooled to the intended commencement of the bent part. The bending is then effected either by a steam-hammer or by affixing a lever and bending the work while on a surface-table.

A crosshead of only a few inches thick can be bent by a few men at one end of a strong lever whose other end is attached to the work. The crosshead is fixed to the table by bolts, plates, and studs being fixed to that end of the work not in course of bending. A strong lever is then bolted to the outer end, and the work gradually bent by means of several heats and sledge-hammerings at the time the power by the lever is applied.

When the crosshead is being forged with a porter attached, the diameter of this porter at the end which is welded to the work should be nearly equal to the diameter of the crosshead end. The porter will then be strong enough to be more conveniently used as a lever than a separate one that needs to be attached.

The bending of a large crosshead is readily effected without a porter. To commence the bend, the work is placed beneath a steam-hammer and across a bottom tool or hollow anvil-block. The upper side of the crosshead is that intended to be the hollow side after the work is bent. While in this position, a few blows are administered to the work, by which it is partly curved or angled, according to the shape of the top and bottom tools, or hammer and anvil-block.

After being thus slightly bent, the work is again heated and cooled to the proper distance, and a tongs is attached to the middle of the crosshead, which is then placed end upwards under a steam-hammer of sufficient height, the lower end being tightly fixed in a recessed tool or anvil-block. A few blows are then struck to complete the necessary angling; or if a great length of metal were heated at the time of bending, it will be curved instead of angled.

One end of the work being thus managed, the other end is treated in a similar manner. The bosses for the piston-rods are next shaped, the centre-pieces put into position, and the arms lengthened and trimmed to the form desired, which is either curved or angular.

A substitute for these processes of shaping the arms consists in making a straight crosshead whose thickness or sectional area is about a sixth greater than that of the circular mid-portion when forged. The angular form is then produced by partly cutting and trimming on the anvil, and afterwards by the planing process.