To make an axle represented in Fig. 121, having a disc at each end, it is necessary to use about three principal components, if the shaft is to be only three or four inches in diameter; but for axles of larger dimensions five, six, or eight components are required.

When only three pieces are to be used, one becomes the crank, which may be either solid or having a short fullered gap, as indicated in Fig. 189. The two other components become the discs, having a portion of the axle solid with each disc. These two are first forged together of one rod, as denoted by Fig. 190; after which the work is divided into two at the middle, and the required disc ends produced.

If the lump selected for the discs is cylindrical, its diameter is equal to the forged diameter of the required discs; but if the shape is four-sided, eight-sided, or any other shape except cylindrical, the shortest diameter of the lump must be equal to or greater than the disc's diameter. This shortest diameter is the distance between those two opposite sides of the lump that are nearest to each other; and the only proper mode of measuring this distance is by means of callipers of suitable dimensions. If the shortest diameter is thus found to be equal to the disc's diameter, no upsetting is needed ; but, on the contrary, a small amount of reducing and rounding is admissible, by which the work is made circular and to the diameter of either of the intended discs.

When the piece is thus reduced to proper shape and diameter, the thicknesses of each disc are added together and marked upon the mid part of the work. If the forged thickness of each disc is to be four inches, the marking is effected by putting two indentations into the work with a fuller, the distance between the two dents being eight inches, the length required for both discs.

Being thus marked, the work is heated to nearly welding, and a pair of fullers fixed, one into the hammer-head and the other into the anvil-block, the fuller ends or extremities being; as nearly as possible, opposite each other; a pair of side guides also are fixed at the sides; and when the work is sufficiently heated, it is put as nearly as convenient into the horizontal position, and upon the bottom fuller. While thus lying, the chain- is adjusted until one of the two dents is brought exactly beneath the hammer fuller, which is then driven in three or four inches, and the worked turned downside up; after which, the fuller is again driven in a few inches, and the work is next adjusted to be fullered while at right angles to its former position. This is effected by placing the two newly made gaps opposite the pair of side guides, and, when adjusted, the fuller is again driven in, and the work put upside down, as at the first fullering. After the four recesses are thus made into the work from opposite sides, the four corners produced in the gap are next driven down with the fullers, and a circular gap or recess around the work is the result; and when the gap is once regularly made, it may be further deepened without trouble.

After one gap is thus made, the other gap is formed in a similar manner, and eight inches distant, as required, being made at the other dent, which indicates the extremity of the other disc. When both the circular recesses are formed, the work appears as in the Figure (190).

Well-formed gaps of this character may be made also by means of semicircular concave fullers, both top and bottom; side guides not being necessary in such cases.

Drawing down the two ends to the diameter of the axle is next performed ; after which, the work is cut into two pieces, the division being made in the middle of the lump. This cutting is effected with the concave bottom chisel, as used for other similar work, when a clean right-angular cut is necessary. During such cutting off of large work the chisels are prevented becoming too hot, through cooling the hammer-chisel by means of a ladleful of water, and cooling the anvil-chisel by applying a mopful of water.

When the two components are thus made by cutting the work into two, each disc is trimmed, flattened, and finished to its forged dimensions. The axle ends projecting from the discs are next cut to a suitable length, and shaped for welding to the two short axle ends of the crank-piece. And after the three components are united, and either stretched or upset to the precise length required, the forging is complete.

A two-disc crank-axle, of ten or twelve inches diameter, may, in some cases, be conveniently made of six or seven pieces, as shown in Fig. 191.

The seven components include the middle piece for the solid crank, the two axle-pieces to be welded to the crank-piece, also two other axle-pieces to lengthen the axle ends to the desired lengths, and the two portions for the discs.

The forging of all the components may be conducted at one time, at different furnaces and hammers ; by which the work is, completed in about a quarter of the time that would be required for forging at one furnace only.

To make the crank part, a pile of bars are welded and cranked, or allowed to remain solid in the ordinary manner. The straight axle-pieces, also, are produced by either piling or drawing down a thick lump, and the two discs are made of flat cakes or circular slices. The mode of making and attaching discs is described in the section on intermediate screw-shafts. When a crank-shaft is being made in this manner of several pieces, the attachment of the discs should be the joints last made.