A considerable amount of turning is executed upon a propeller-shaft; its disc being turned, its middle part turned to suit the packing-bushes, its cone turned to fit the propeller-boss, and a thread sometimes formed, which is situate beyond the cone to fit a nut whose face is screwed tight against the boss.

If a propeller-axle is to be furnished with gun-metal linings or coverings for contact with the packing-bush or tube, the portion of the shaft on which the lining is to be situate, must be either larger in diameter than the rest of the axle, or smaller. If larger, the portion can be truly turned, and separate bushes provided which can be placed upon the shaft and fixed with keys and pins. But if such part is smaller, it must be furnished with gun-metal in a liquid state which is poured around the heated shaft, and becomes as if solid with it, so that at a future time it requires cutting off, and fresh metal to be poured around. For this purpose the shaft should have been so forged that the portions intended for the linings are of the finished diameter, and need no turning except at the corners. The shaft is then centred with a rectol, or monto, to cause these smaller portions to rotate truly in the lathe. The larger parts adjoining the necks for the gun-metal, are now to be truly turned, which prepares the work for the pouring. The metal is poured into a mould properly built around the heated shaft, to cause the lining to be of about equal thickness. This process bends the shaft, and requires it to be straightened, which can be done either in the lathe with which the turning is to be effected, or with a proper lathe for straightening in the smithy, before referred to (page 56). When it is straight the truly turned portions adjoining the gun-metal are seen to rotate truly as before bending; after which the turning proceeds to shape the lining, cone, and effect other turning and screwing intended.

The thread for a propeller-shaft should be cut with the same lathe which executes the turning. But when it happens that a long shaft is to be screwed with a comparative short lathe, or one having a comparative short screw, the screw-cutting can be effected while the shaft is situate with its propeller-end next the chuck, as in Fig. 1147. The propeller-nut is of gun-metal to resist the water; but a cast-iron one is suitable, if its face is smoothly turned, and its screw fits the shaft to keep out the water.

The discs or couplings of screw-shafts are also, in some cases, of cast-iron, and keyed in their places, instead of providing forged iron or steel discs solid with the straight portions. When separate discs are employed they are fitted and keyed in their respective places, either previous to finally turning their outer surfaces, or afterwards; because the tightening of the keys will not alter the relative positions of the discs if they are properly bored to fit the shaft-ends.

A long slender shaft during turning, requires the aid of a stay to prevent vibration, and thus enable the tool to cut. A stay for this purpose consists of a pedestal which is fastened to the lathe at about midway between the two ends of the shaft. The upper portion is furnished with bearers which should be of wood, with which the shaft is gripped and thus steadied during its rotation. To prepare the shaft for such a stay, it is gently reduced with thin cuts without the stay, until it rotates truly at the place to be gripped ; after which the apparatus is attached and the heavy turning proceeds.