The Locomotive Of Today

The Framing, Wheels, etc. : Tyres, Axles. 133 The tread is turned off to an inelination of i in 20 to the horizontal thus coning- the wheels, this benig" done so that the face of the tread may be at right angles to the rail centre, as these are usually set at an inelination of about 1 in 20 to the vertical. It has been supposeel, too, that coning the wheels assists them on curves as the engine flies outwards when passing round, and therefore the larger diameter is on the outer rail and the smaller upon the inner, as it should be ; experiments have proved, however, that it is of little if any use for this purpose, but by coning them they always have a tendency to centre themselves on the rails. Ihe driving tyres of six coupled and single express engines are generally made with flanges of reduced thickness, in order to allow a certain amount of flexibility to the engine, and save the crank axle from some of the side shocks received from striking the rails. For the same reason in engines with long wheel bases some of the tyres are made “blind,’ that is with no flanges at alj. They are then about 6^- inches wide, so that freedom to pass curves is obtained, and yet the wheels do not lose their alignment with the other wheels to which they are coupled. The American shape shown at D for the outside of the tyre differs by having a slightly deeper flange, and is wider overall. Usually tyres when new are from 3 to 4 inches thick at centre, and are allowed to be turned up when worn until they are reduced to i| inches at the last turning. They are then allowed to wear | inch below that, but must then be removed, as with such thin metal the application of the brake blocks and consequent generation of heat would expand the tyre and loosen it. Axles are also of open hearth or Bessemer Steel, and are subject to severe tests before being accepted from the con- tractors, the ultimate tensile strength to be 32 tons per sq. in. A piece is taken from the forging and machined to i|-in. square and bent double whilst cold without sign of fracture. With crank axles one is often taken from the parcel and tested to destruction by spreading the webs by forcing wedg'es between them, and they are usually taken on the condition that the makers replace, at their own cost, any that may fail before they complete 200,000 miles. At E half a crank axle is drawn, the wheel seat being at the left, next the journal, then the outside web or cheek, the crank pin, inside web and central portion. The other half is similar, but with the crank turned at right angles to the one shown at E, as will be seen on the end elevation at F.