A class of simply formed two-arm crank-axles is represented by the intermediate axle in Fig. 122. Short axles of this sort, having the bearings at a great distance from the keyed crank-levers, are best when made of one piece; and an intermediate axle of great length, whose bearings are to be close to the keyed levers, is conveniently made of three pieces, the axle-pieces being made of proper length to cause the two joints to be made between the middle crank and the bearings at the axle ends.

To make a short axle in one piece, the lump is selected, or a sufficient number of bars are piled and welded together until a lump of the required dimensions is obtained, the amount of metal in the piece being amply sufficient for the whole of the intended two-arm crank and the two axle ends included. The shape of this component piece should be that of a bar having a thick lump on one side and midway between each extremity, similar to that indicated in Fig. 183. The thickness of the two axle parts is nearly double that of the finished thickness, and are, therefore, much shorter than the finished length; and the thickness and width of the thick lump in the middle are about equal to the thickness and width of the crank required. This thick portion may be formed upon one side, as desired, by piling and welding short bars upon only one side of the primary axle-piece; or by another process the lump can be made, which consists in reducing a thick short bar at each end of the intended lump, allowing it to remain between. When drawing down is adopted, the thick portion is made to project from one side of the bar by means of drawing down, without turning the work upside down, the lump, by such treatment, being produced from the upper side.