Two-throw crank-shafts are made by first forging two separate cranks, either with gaps or without, and afterwards welding two of the axle ends together; the joint being between the two cranks. Whether the cranks are to have curved extremities or angular, the desired shape is produced previous to the final joint-making.

One of the two cranks is placed at right angles to the other by means of the joint; this is made to fit and coincide while the two cranks are at right angles to each other, and welded in that relation. The particular relative position of the joint ends with the cranks is of no consequence, because the joint is thoroughly welded by upsetting while in the furnace; but the situation of the joint may be at any convenient distance from either crank. To make a good joint a large mass of metal is provided, to admit two or three welding heats; after which the joint part is reduced to the forged diameter of the axle. By this treatment the extreme ends of the original joint become extended to a great distance along the axle, and are so amalgamated with each other that the men who made the joint cannot tell either its situation or position.

Two-throw crank-shafts are made also by piling up the cranks on the sides of a primary axle-piece. This piling is- of sufficient height and in the required places to form the cranks to the length desired, and also at the required distance from each other. Each of the piles being at right angles to the other, the cranks are produced in the required relative positions, and without much twisting of the axle or making a joint between the two cranks. At the conclusion of forging, a small amount only of twisting is necessary, to adjust the cranks to a right angle with each other. Cranks thus forged are shown in Fig. 199.