A large crank axle of about five, ten, or twelve inches in diameter, requires rather different treatment to that for a small one only a couple of inches in diameter, principally in consequence of its greater weight. It is, however, always advisable to use vee-blocks for large axles in about the same way as for small ones, because the portable cranes now employed will easily lift and move heavy objects to and from a lining or planing table, and also alter their positions as required while on the table.

To centre a crank-shaft without vee-blocks, it is suspended with a crane and marked with a gap straight-edge or rectol. Rectols having gaps of suitable shapes for cranks are indicated by Figs. 1135 and 1137 ; and an implement of this class in use is seen in Fig. 1136. By means of a rectol being placed in contact with the axle-portions at both sides of the crank the centres are shown with regard to the parts adjoining the cranks, and also the ends; and if the axle is crooked the centring will cause the crooked parts to rotate about as truly as the straight portions. While a rectol is in contact a calliper is adjusted, and placed upon the outer edge, to make marks upon the axle-ends, in the same manner as described in pages 348 and 360, for centring bolts and straight shafts.

A monto also can be used to centre a crank-shaft, if the vee-blocks of the implement are tall enough to keep the straight-edge part from touching the shaft. A long straight-edge and a couple of parallel blocks also can be employed as a substitute for other implements.

When the shaft is centred and coned, the rough-turning proceeds while a packing-block, or blocks, is in the crank-gap. This packing is required to resist the pressure of the poppet-pivot imparted to the shaft in the direction of its length, and also to assist in steadying the shaft against the strain of the cutting tools. As soon as the axle-ends are turned along their lengths. the adjoining two sides of the crank, also turned, and a portion of each end turned to one diameter for resting in the vee-blocks, the ends can be fitted to the pivot-carriers.

The pivot-carriers are required for turning crank-shafts' crank-pins ; and are two in number, one situate on each end of the shaft. Implements of this class are indicated by Figs. 1138 and 1139. Each carrier consists of a kind of lever which is to be tightly fixed on a shaft-end so that one end of the carrier shall be opposite the crank-pin portion. In this condition a conical recess can be made into each carrier, to fit the lathe-pivots; consequently, while the shaft is thus supported, both it and the carriers can revolve around the axis of the required crank-pin.

An axle having its two pivot-carriers attached ready for turning, is denoted by Fig. 1141. Each carrier is furnished with a circular hole the diameter of which is amply large enough to allow the shaft-ends to be reduced after the crank-pin is finished; and if a number of axles of the same size are to be turned, all the ends are accurately fitted to the holes in the carrier! so that the same pair may be used for all. Each carrier-hole has a key way, that a headed key may be inserted to avoid risk of shifting. The axle-ends are smoothly turned so that the carriers can be easily hammered upon them and be easily removed, being only tight enough to prevent looseness when attached.

Adjusting the carriers to the proper positions on the axle, is performed on a lining-table or planing-table, while resting in vee-blocks, as in Fig. 1140. The operation consists in placing them and marking them at the same process; and when the two carriers have been placed upon the shaft to somewhat near their intended positions, the axle is lifted and maintained with its crank lying near the table, by means of a few packing-blocks, as in the Figure. The carriers are now keyed tight in their positions in which they are to remain during the turning, their outer sides being nearly level with the extremities of the shaft. A straight line is marked along the crank, as soon as it is put parallel with the table, in order to show the centre of the crank, and the centre of the crank-pin also, which line is indicated by C. The line is scribed parallel with the table so as to extend across the axis of the shaft, by reason of the Drank being kept at the proper height with the packing-blocks.

When the centre line existing on the crank is adjusted to parallelism with the table, by referring to the scriber-block, the block is moved to the carriers, anil a line scribed along each of their outer sides, one of which is seen denoted by P. These partly indicate the places for the intended centre-recesses, because they are marked at exactly the same height from the table as the gauge-line C. It is nest requisite to mark the length of the throw upon each line P. and thereby complete the centring of the two carriers.

By this method, the axis of the crank-pin is indicated exactly parallel with the axis of the axle, which is required; and a small circle is nest scribed around each centre, and dotted, that the centre may be afterwards found if necessary, when the conical recesses are made.

In addition to scribing the length of throw upon the carriers, it is requisite to scribe the centres for turning the extremities of the crank or lever-ends. These centres are marked upon the same fines on which the crank-pin centres are situation, both being equidistant from the axis of the axle. But this distance depends on the intended length to which the lever-ends are to extend from the axle; therefore the length is ascertained and the centre scribed accordingly. One of these is denoted in Fig. 1141. by M.

The turning now proceeds by first turning the lever-ends just referred to, in order that the crank may be thus caused to occupy as little room as possible during the turning of the crank-pin, and thereby generate as small a circle of revolution as possible. These lever-ends can be entirely finished at this turning. The work is nest shifted, and caused to rotate on die crank-pin, the gap being first widened, to allow room for the long slide-rest took to operate at the bottom of the crank-gap to shape the crank-pin. During these operations the crank is staved with the wood packing-blocks indicated by B and B. in the Figure (1141) situate in fine with the ask of the crank-pin. After the stays' have been fixed, they must not be shifted until the turning of the pin is finished, especially if it is very nearly reduced to the specified dimensions. By drifting the stays, and also by adjusting them, the crank is liable to be sprung or bent to some extent.

During the turning of the crank-pin. the slide-rest took should be supported at their cutting ends. This may be effected either with a screw-bolt and nut with a lew packing-pieces, or with a tall wood block of proper height which is fastened with a wedge. By either of these appliances, the tool can be effectually supported during all the rough and smooth turning which is executed with the lathe's four traverse, because the supporters, when fixed, rests on the lathe-carriage, and therefore moves with it in conjunction with the tool The supporters should be used also when finishing the crank-pins curved corners with the slide-rest, but without the long inverse motion; because, although during the finishing the tool is moved independently of the carriage, the amount of movement not enough to interfere with the easy operation of the cutting-tooL The fixing of a supporter beneath a tool-end, consists in gently tightening the wood prop with the wedge, or the screw-bolt with its nut, after the tool has been properly placed and fastened in the slide-rest; and in the case of a prop bring applied to a tool for finishing a corner, the tool is first advanced to about a sixteenth from the corner, by working the slide-rest screw, and the prop is then fastened in the desired situation rank-pins are finished with springy took and soap solution The took should be made of thin bar-steel and are to be used in conjunction with a thick slide-rest tool, or a dummy, on the top of which the spring tool is fastened Took of this class are also used for planing, and are indicated by Figs 711 and 712.

One of the author's props for crank-turning consists of a screwed rod having a clasp at the upper end, the dan being fastened with a little fixing screw to hold it to the tool The clasp also swings around the rod or prop, so that it can be fixed at either side of the tool, and not come into contort with die crank during its revolution, however near the edge of the tool may be to the edge of the crank.

After the crank-pin and adjoining rides of the gap are finished, toe pivot-carriers are removed, and the axle-ends are to the specified diameters and length. During this turning one stay is required, and is gently wedged in toe crank-gap without distorting it-