An axle having two cranks k fined and centred for the first turning of its axle-parts, in the same manner as a single-crank axle, either by placing the axle into vee-blocks and scribing with a scriber-block, or by using a gap straight-edge and marring with a calliper. The rough turning of the axle next proceeds, together with the turning of the four crank-sides adjoining the axle. If a great quantity of metal is to be cut off, it should be done previous to cutting out the gap-pieces of the cranks with the drilling, slotting, or sawing. While the cranks are devoid of gaps, the shaft is not so liable to tremble in course of turning.

As soon as the axle is reduced so that two portions are of one diameter for resting in the vee-blocks, the two ends turned to fit the pivot-carriers, and the gap-pieces cut out, the lining for turning the crank-pins proceeds on a table with the aid of vee-blocks used as for a single-crank axle. For this lining two centre lines are requisite, one on each crank, both being analogous to the line C in Figs. 1140 and 1141. The two lines on a two-crank axle are indicated by C and C in Fig. 1142. These are required to be right-angular to each other, and also properly situated to pass through the axis of the axle. The first step, therefore, is to put the scriber-block to each centre recess, to see if the axis is exactly parallel with the table; if not, by reason of a difference between the vee-gaps, or other cause, it is easy to pack up one block with a thin packing-piece. The axis bein gnow parallel, that crank which is lying near the table is put as near to parallelism with the table as the rough surface will allow, by merely measuring with a calliper the distance of both ends of the crank from the table. The shifting for this purpose consists in merely rotating the axle a short distance in the vee-gaps; and when the crank is placed, the scriber-block, with the point adjusted exactly to the height of the shaft's axis, is put to the crank, and a line scribed along it, which is one of the centre lines C required.

To mark the other centre-line upon the other crank, the shaft is rotated a quarter of a rotation, so that the line just marked may be put square to the table. An el-square is therefore put close to the crank, which is now upwards, as represented in the Figure (1142), and the distance between the edge of the blade and the line is measured with a compasses at top and bottom. By this means, and rotating the shaft a little, the line is placed right-angular, and the entire shaft into position for scribing the other centre line upon the other crank, now parallel with the table. Therefore, the scriber-block, with the point of its scriber at the same height as before, is put to the crank and the line scribed. Both lines are next dotted along their lengths, that they may be easily referred to in the event of some portion getting erased.

The second centre-line can be marked also with a square and scriber, instead of with the scriber-block. In this case the centre-line marked on the first crank is put parallel with the table, without regarding the other crank which stands at right-angles. In this position the square is put to the crank standing up, and at both sides of the axle, so that two parallel lines are marked from top to bottom of the crank; after which the desired centre line is placed parallel with those marked with the square. Large cranks can have their centre lines marked also by means of right-angular cross-lines, which are marked upon the smoothly-turned shaft-extremities. This mode suits taper cranks belonging to axles of large diameters. Also, by using the author's gap-square, only the one centre line need be scribed.

The two centre-lines now exist right-angular to each other, and are next referred to for adjusting the pivot-carriers to their proper positions on the shaft. These are therefore put upon the shaft with their ends opposite the crank-pin to be first turned, the centre-line along each carrier being parallel with the table, and so that their outer surfaces are about level with the shaft-extremities. In this condition the shaft-ends are scribed for the key-ways, which is done by moving a scriber along inside the already-finished key-ways in the carriers. The key-ways are next cut, the keys well fitted, and the carriers again put upon the shaft to be keyed tight. Both of them are to be now lined, to show the places for the centre-recesses. This is partly done by placing a scriber-block to each carrier and marking a line along their middles while the scriber-point is at the same height as the axis of the axle, and while the centre line of the crank to be first turned is parallel with the table. To finish this marking it is now only necessary to mark the length of throw and the places for the two middle recesses upon the two carriers, measuring from the shaft's axis. While marking the length of throw, a compasses, or wire gauge with pointed bent ends may be used, and the outer surfaces of the carriers may be situate as far inside the extremities of the shaft as the depth of the recesses. This will cause the length of throw to be correctly scribed while one point of the gauge touches the bottom of the drillhole, and the other point is scribing an arc across the centre-lines on the carriers.

The conical recesses can now be made into the carriers, and the crank-pin and gap-sides finished; after which the carriers are removed from the shaft and again fixed for turning the second crank. This fixing is quickly done if the carriers were previously correctly fitted with regard to their circular holes, their keys, and key-ways. To fix them the second time the axle is put upon the vee-blocks, and the crank to be turned is put parallel with the table ; therefore in the same position as the first crank at the previous fixing. On this occasion the centre lines on the two carriers and the centre line on the crank to be turned are all put parallel with the table. Being thus adjusted, the places for the second couple of shaft key-ways are accurately marked by moving a scriber along inside the carriers as before. The key-ways are next cut and fixed to the lines, which will cause the three gauge-lines to be parallel with each other when the keys are driven in and the carriers fixed. This marking of two key-ways in the proper places, and fastening the carriers thereby, prepares the work for turning the second crank-pin without in any way altering the centre-recesses, the same recesses being used for the second crank as for the first.

It may be here noticed that it is scarcely possible to so accurately form the key-ways that all the three gauge-lines shall be exactly parallel with the table when the carriers are finally fixed ; but any careful fitter can form the key-ways so that the lines shall not diverge more than a thirtieth of an inch from parallelism. Such small divergence merely causes one crank to be not quite right-angular to the other, supposing that both carriers are caused to diverge in the same direction, and such a difference is of no importance. The length of the throw cannot be affected by error in the key-ways. It is, however, usual to try the lines previous to finally widening the key-ways, at the time the keys will enter only a short distance. At this stage the shaft is moved and the scriber-block put to the lines, which will indicate which sides of the key-ways require most filing.

In order to balance the overhanging metal of the shaft and its crank or cranks in the lathe, balance-weights are fixed either to the lathe-chuck or to the pivot-carriers. If attached to the carriers, a hole is provided in one end, to admit a stem or rod, on which weights of any convenient sizes are bolted, and at the distance from the axis of rotation desired. Stems of this class are seen attached to the carriers denoted by Figs. 1138 and 1139. Adjustment of the weights, therefore, consists in shifting them to their proper places while the lathe is at rest, observing whether the chuck will remain in any position in the course of its rotation.

To turn the cranks of an axle having discs, the discs can have holes drilled therein, and the carriers be attached with bolts and nuts. Or, if a shaft having only one disc is to be turned the disc-end can be provided with an extra length of shaft, on which portion one carrier can be keyed. This is the mode adopted for the shaft in Fig. 1142.

To turn a single-arm crank situate at one end of an axle, only one pivot carrier is required, and is fixed at one end, as in Fig. 1143.

It is necessary to here mention how crank-pins of solid cranks can be shaped without requiring the fitting of distinct carriers, and also without involving the revolution of a great weight of overhanging metal in the lathe.

Single-crank axles with the cranks situate at some distance between the two ends can be, in nearly every case, forged with superfluous crank-arms or levers, each axle having two, one at each end, and solid with the remainder of the shaft. A crank thus forged is shown by Fig. 1144. It is easy to place the two arms so that they extend from the shaft in the same direction as the crank, and they can be easily centred after the axle has been partly turned, as described for other cranks. When the crank-pin has been finished by such means, the superfluous arms are cut off with drilling and slotting, and the axle-ends finished.

Superfluous arms of this character would not be so serviceable for two-crank axles, because four arms would be required; and their cutting off would occupy nearly as much time as fixing two distinct carriers. But in the case of only one crank-shaft of a size being in progress, and no pivot-carriers existing for the turning, it is decidedly preferable to forge the shaft with the carrier-arms, whether it has one crank or two, or whether small or large. It is preferable to cut off the arms, rather than to cast new carriers, fix them, and detach them.

An axle having only one crank with its crank-pin existing at one end of the shaft, requires but one superfluous arm - to exist at the opposite end - which allows the turning to be done with a centre-recess in the crank-pin, and a centre-recess in the extra arm.

An axle with two discs requires a piece to be forged solid with each disc, the piece extending from the proper side of the axle and to a sufficient distance. This arrangement will be found very effectual for a disc-shaft, especially if the throw of the crank is short, as often occurs, in which case the extra pieces will need to extend only a very little beyond the discs, and can therefore be easily turned off with the lathe without any previous drilling.

The crank-pins of shafts can also be easily shaped while the entire shafts and cranks remain at rest. For this purpose rollions are employed. A rollion is a paring-machine, which mainly consists of a table similar to a planing-table, and a revolving apparatus which travels around an axis which is parallel with the table. A shaft requiring its crank-pin to be shaped is first lathe-turned sufficient to entirely finish the axle-portions, after which it is put upon the table of the rollion, the axis of the shaft put parallel with the table, and the axis of the crank-pin put into line with the axis of the revolving cutting apparatus or head, in which position the crank-pin is shaped. There are several sorts of rollions in Britain and the Continent, those having their tables situated vertical being suitable for short crank-axles, and those with their tables horizontal being best for heavy axles of great length. By using a horizontal table it is not necessary to fix the length of the shaft vertical.