To avoid the upsetting that was stated to be necessary for welding tongue-joints, another kind of joint-making is adopted, by means of which welding is accomplished by ordinary drawing with a hammer.

With this intention, all the necessary components of the shaft are united during the original piling together of the constituent bars ; and the shapes of the joint ends are those of long forks. Such a fork is obtained by welding together two bars at the middle only; and when the loose portions not welded are opened, a piece having two fork-prongs at each end is the result. Any required number of these original constituents may be employed, according to their thickness and the desired dimensions of the shaft to be produced. When only two or three such forked pieces are to be used, and welded together end to end, they may be fixed in position by closing the four ends with hammering, previous to placing them in a furnace for a welding heat. But when five, six, eight, ten, or any greater number of such pieces require piling and welding upon top of each other, or side by side, instead of being united at their ends only, the pieces are bound together with binders, which are attached whenever fresh piles are added. Fork-joint piles are shown by Figs. 179 and 180.

This method of interlaying and piling is applicable to paddle-axles, or any other axles of similar shape, and also to the cylindrical portions of crank-axles, whether small or large. By thus uniting the forked constituents, welding them together and forming a square bar, a cylindrical shaft of good quality can be afterwards produced, without any upsetting of tongue-joints.

Middle Shafts (Fig. 178). - A middle shaft, or middle axle, is that which is between the two paddle-shafts, and also in the middle of the ship. The simplest class have no crank forged solid with the shaft, but are of cylindrical forms resembling paddle-shafts. Two crank-levers are keyed to a middle shaft, one at each extremity; instead of only one at one extremity, as on a paddle-shaft.

At each end is a bearing, adjoining or a few inches from each crank-lever; the forging of such a shaft is therefore similar to that for a paddle-shaft, the smith exercising the necessary care to make the joints in their proper places, and to well close the bearing-parts, although it is not necessary to hammer the work sufficient to harden the metal at the centre; this portion may be fibrous throughout the total length of the work.

The mode of procedure resembles that for a paddle-shaft, and much depends upon the shape of the iron at the disposal of the workmen. The quality of the metal is the same as that of all other engine-axles, where iron is employed, and should consist of new puddled bars.

When convenient, these bars are made into a pile and welded by steam-hammering the mass into a shape of a short thick bar, or into the form of a cubic lump. In these cases, the porter which is used for reversing or rotating the work is welded to the middle bar of the pile; and thus remains solid with the work until the shaft is forged. But when a cubic lump is selected from a piler or shingler, the engine-smith welds one of his own porters to the piece selected.

A convenient and safe mode of attaching the porter consists in making a gap with a steam-hammer fuller into one end of the piece, and placing into the gap a porter whose extremity is rather thicker than the part next adjoining; the gap is next closed, and becomes what is termed a dovetail joint. This class of porter attachments is shown in Fig. 172; when thus prepared, a welding heat is given to the joint, and the work is fit for drawing down to the required dimensions of any cylindrical shaft that is desired.

While finally reducing a middle shaft or any other shaft of similar character, gauge-blocks may be conveniently used. These blocks are on the anvil, and packed up to a height from the anvil which is equal to the required diameter of the work. The shaft is then slid along between the blocks, and reduced until the hammer strikes the gauge-blocks at the same moment as the work ; by which the proper diameter is attained without making any part of the shaft too small, the rotator being used for reversing the work in the ordinary manner. By this mode of finishing, the amount of smoothing required with half-round tools is very small, the circular shape of the shaft resulting from its rotation by the workmen.

The larger the shaft, the greater is the necessity for clean orderly cuts at the conclusion of the forging, to make the extremities of the work at right angles to its length. A few of the methods for attaining this end shall be described.

One mode for producing a right-angular cut consists in using a straight chisel which fits a steam-hammer, and also a broad arched anvil-chisel which fits an anvil-block, so fixed that, when the two chisels are put together, both cutting-edges are opposite each other. By then placing the shaft into the horizontal position upon the anvil-chisel, and striking with the hammer-chisel, two cuts are commenced around the work; and if both the cutters are properly fitted, the incisions will be opposite each other, and, by slowly rotating the work during the cutting, each cut will be continued until both meet, forming a cavity or incision around the shaft which is at right angles to its length, as desired. After this, the cutting off is completed by the hammer-chisel only, the bottom anvil-chisel being taken away.

A right-angular cut is produced also by fixing a pair of half-round bands or clips to the shaft, so that the distance between the extremities or faces of the bands and the intended cut shall be equal to the breadth of the half-round anvil-block on which the work is to rest while cutting off is effected. While putting the shaft into the horizontal position for cutting, the chain that suspends the work is wound out, or what is called payed out, towards the centre of the hammer, so that the clips shall bear tight against the anvil-block while the shaft is being rotated by the men, and also while the hammer-chisel is being driven through the work. The shaft being thus prevented from moving forwards or backwards, and the chisel being fixed in the hammer-head, causes a square cut to result, however thick the shaft may be, and however quickly the chisel may be driven through, or the work rotated.

A third method of cutting off is managed with a chisel having a long handle held by a workman, or two or three workmen ; so that one part is kept close to the side of the bottom tool, while the other part of the chisel is driven through the work with the hammer, the shaft being rotated by the men in the usual way.

While measuring for the final cutting to length of any large shaft, it is proper that the work be as nearly cold from one end to the other as circumstances permit. The work may then be cut much nearer to the finished length than by allowing a large quantity for lathe-turning, or for shortening of the work while cooling.