When speaking of engine-making, the name rod signifies a transmitter of motion or force from an active agent to a passive object. And in all cases where practicable, the sectional area of the rod is greatest midway between the two ends; because, when the rod is parallel, the centre or mid-portion of it is weakest.

The variety of rod indicated by Fig. 23 is sometimes made by upsetting each end to form the circular portions termed bosses. This mode is tedious, and requires much welding if the iron should not be very soft and tenacious ; consequently, upsetting is seldom adopted except for small work, or for work which is short and thick.

A very efficient mode for general work consists in preparing a bar to the suitable diameter for producing the bosses by a small amount of upsetting, and a small amount of reducing to form the intermediate portion. If the boss portions are upset, curved, and welded, a circular arrangement of the fibres is obtained, which ensures the necessary solidity for the boss after the holes are bored.

After the boss is upset, while at welding heat, and the extremity put into a circular form by hammering, and by large curved rounding-tools, top and bottom fullers are driven in to form the inner extremity of the boss, shown in the figure by A. By this means the whole of the fibres in the boss are put into a circular arrangement, which is a desideratum. The intermediate portion of the rod is then reduced to its proper diameter and shape, and the length increased to the length desired.

This method of making such rods is very economical, and produces a solid kind of work without waste of metal, if the piece was originally cut to a suitable length, ascertained by application of the rule in page 8.

Another mode of proceeding is by making separately each boss with a short stem; these stems are then scarfed, and welded to the intermediate portion, which may be of the diameter required, to avoid reducing. When this plan is adopted for long heavy rods, a tongue-joint is made, instead of a scarf-joint.

To produce a good tongue-joint, the two ends to be welded are upset, either by Daviess patent striker or by a pendulum-hammer. The length of the upset part is about equal to the length of the rod's diameter previous to upsetting; after being upset, the diameter is one-third longer than previous. After the two ends are upset, the taper part, named the tongue, is drawn down from one of the pieces, by first driving in a broad fuller, at a short distance from the extremity, and from two opposite sides of the rod or bar. The fuller is driven to a short distance only, and the lump that remains is conveniently tapered by the patent striker, which is adjusted to deliver its blows at an angle of 45° or 60°, as desired. During the tapering, the work may be placed along the top of an anvil, or the anvil may be shifted to suit the position of the striker, and the work laid across the anvil.

The opening, or orifice in which the taper end is fitted, is named the mouth ; and is produced by cutting open the end with a chisel, and afterwards enlarging by driving in a wedge. The use of the wedge produces a large mouth without the necessity of cutting out a large piece of the iron, which may be needed during the heavy blows when welding and rounding is being performed. The depth or length of the mouth from the extremity of the rod should not be more than twice the length of the rod's diameter, to prevent the joint-edges becoming too thin while being reduced or rounded after being welded.

The next operation is shaping those portions of the mouthpiece which will receive the hammering during the welding. These portions are curved, either by hammering or by a trimming-chisel; this curving prevents the hammer from spreading out the outside of the mouthpiece and making a series of thin ragged edges. And if the hammers or rounding-tools are thus made to strike a curved lump, instead of an angular projection, the iron is closed in towards the centre of the rod, instead of being spread out at the circumference.

After the mouth and tongue are properly prepared, the stock near the tweer is mended, or made anew if necessary, and the two pieces are laid together in their proper positions in the fire or fireplace. And if the work is long and heavy, each piece is supported by a crane at each side of the forge; the endless chains around the work allowing it to be rotated to expose the entire circumference to the action of the blast, that one portion may not become heated previous to another. In order further to promote a proper distribution of the heat, the fire is of the two-stock character: one stock being opposite the other stock near the tweer. Both stocks as built gradually taper upwards to four or five inches above the work. The stocks are well hammered and battered together ; and a thick arch is built, which is supported by each stock, and prevents the heat escaping. A good arch is made after the work is laid in the fire, by laying sticks of wood around the top of the work, and piling to five or six inches thick. Pieces of coke and coal are then placed upon the wood, and among it; and wet small coal is then put into all the cracks and piled up, and battered closely together. After the wood is consumed, the arch remains, and the only escape for the flame is by the two openings at the sides of the fire. These two openings are also partially closed, when necessary, by placing pieces of coke that are heavy enough to withstand the force of the blast.

When the welding heat is nearly attained, the blast is moderated, and while gently blowing, a large supply of sand is administered through the two openings or outlets for the flame. The ladle having a long handle is used for applying the sand, which causes much of the slag which is formed around the joint to slip off the work into the fire, instead of being welded into the joint.

When the welding heat is reached, the joint is welded while in the fire, by striking the end or ends of the work with a pendulum-hammer. These blows are very effectual for welding the joint to the extreme depth of' the mouth, if the iron is properly heated to the centre, which cannot be done by hasty urging of the blast. The outside will in all cases become a few degrees hotter than the middle; but, with ordinary care, the difference is not sufficient to prevent a pood weld and a good joint. After being welded by a pendulum-hammer, or as it is sometimes termed, an oscillating-hammer, the work is taken from the fire by swinging out the two cranes to place the joint upon an anvil; or the work is conveyed by a truck and railroad, if necessary. The welding of the joint is then completed by hammering, or by large angular-gap tools, which are effectual for closing the iron and welding a greater part of the circumference at one blow than could be welded by one blow of the hammer only. For steam-hammer work, the angular-gap tools are very thick and strong, to avoid liability to break while in use. Large tools of this character are not used for ordinary sledge-hammers, because the blow given by such a hammer would have no visible effect upon the work beneath, the force of the blow being absorbed by the metal which constitutes the tool.

Whether it is more economical to punch and drift the eyes or holes in the bosses, or to leave them solid to be entirely bored by a boring or drilling machine, cannot be decided in any general manner. If a man possesses a number of good boring machines, he may prefer to cut out the lumps by boring-bars and cutters, because he may not have much forging machinery. In most cases, it is both quicker and cheaper to drift the eyes to a proper diameter, leaving only sufficient metal to bore out to the dimension required. If, by punching and drifting, a large hole is made, a large boring-bar can be immediately inserted; but if a little hole only is made, it is almost as useful as none, because an extra boring-tool must be used to admit a large boring-bar of suitable diameter.

And in addition to an economy of time and metal by drifting, there is the advantage of securing an approach to a concentric disposition of the fibres in the boss. This disposition is attained by the metal being swelled out by the drift, and by being well hammered and stretched while the drift is in the opening.

The making of large holes or eyes will be again treated in the portion devoted to crank-lever forging.