One-arm crank-shafts are sometimes made solid with the crank-pin ; in these cases, three principal components are required, instead of only two.

To make a shaft of this sort, an opening may be made into the shaft end by punching; or, instead of this, the lever end may be split open and the two ends bent together around the shaft; and the other end of the lever requires similar treatment for being welded to the crank-pin. By this method the pin is first fitted to the lever, and the other end of the lever is next adapted to the shaft. When both joints are prepared, the first joint welded is that of the pin with the small end of the lever, after which the other end of the lever is welded to the shaft. The three components together are represented by Fig. 182.

Of the three components, the first prepared is the crank-pin. This is reduced to its finished forged diameter, and a thick part allowed to remain at one end for the joint, and is shaped for either a tongue-joint, or for an oblong hole in the lever, or for a gap similar to that shown in the Figure (182). The small end of the lever is next prepared, and the crank-pin joint then welded and finished, after which the shaft end of the lever can be cut and prepared so that the lever shall be about the proper length when welded to the shaft. The welding of the lever to the shaft is next performed, and the lever adjusted to its required length.

From the centre of the shaft to the centre of the crank-pin is the length of the lever's throw; and, after deciding which shall be the centre of pin and which the centre of the shaft, the smith lengthens or shortens the lever to that which is desired. Adjusting to length is effected by heating the lever to a yellow heat in the mid-portion and upsetting it, if too long; or by laying it upon one side and drawing it, if too short.

When the proper length is attained, the superfluous metal is cut from the lever and from the bosses, and the work is shaped with fullers and rounding-tools until the necessary curves for the bosses are produced.