Screw-Shafts

The screw-shafts of a pair of engines properly include the crank-shaft, all the intermediate shafts, and the propeller-shaft; but the intermediate shafts only are here meant. These are connected to each other and to the crank-axle by means of circular discs, bolted together with screw-bolts. In order to cause any set of screw-shafts to be fastened together in line with each other without improperly straining the connecting-bolts, the outer surface of each disc is truly turned while in the lathe to make them all square to the lengths of the shafts. The inner surfaces of the discs are also turned, that the bolt-heads may bear properly. No other turning need be executed for a mere intermediate shaft, unless it is to have a pillow-block.

Thrust-Axles

A thrust-axle is usually one of the intermediate axles, and its thrust part should be situate near one of the discs, that the turning of this portion may be performed at a part not liable to tremble during turning. The thrust part is always forged devoid of any groove, in the condition denoted in Fig. 1146. The thrust-ridges are produced first with grooving-tools, next with narrow right-hand and left-hand corner-tools, and finished with narrow spring tools.

In order to cause all the ridges of a thrust-portion to fit and bear equally against all the ridges of the thrust-block, a pair of sheet gauges are used - one fitting the block, one fitting the axle, and both fitting each other.