56 RAILWAY CONSTRUCTION. 



Figs. 39, 40, and 41 show sketch elevation, plan, and trans- 

 verse section of one pattern of four-wheel bogie truck largely 

 adopted in American carriage stock, and although there are other 

 types varying in detail, the general principle remains the same 

 in all. The diagram sketch (Fig. 42) represents the two bogie 

 trucks slightly swivelled to adapt themselves to the curve round 

 which the carriage is supposed to be passing. 



For carriage or waggon stock with an independent bogie 

 truck at each end, the central pivot and swivelling motion 

 supply all the freedom that is requisite ; but for locomotives it is 

 necessary to provide for lateral as well as for swivelling move- 

 ment. The driving and trailing wheels and sometimes one or 

 two other pairs of wheels work rigidly in the frames, and as the 

 normal position of the centre of the bogie truck must be in the 

 centre line of the engine for the straight line, it is evident that 

 some appliance must be introduced to allow the truck to move 

 laterally when the engine has to traverse the curves. 



Figs. 43, 44, and 45 give sketch elevation, plan, and transverse 

 section of a swing-link bogie truck as applied to an ordinary 

 American locomotive. Its recommendations are its simplicity, 

 its efficiency, and its accessibility for inspection and lubrication. 

 The swing-links, which provide for the lateral movement, are 

 direct acting, and do not require any side springs of steel or 

 indiarubber. All the principal parts of the bogie are visible 

 and not mysteriously cased in with plate-iron boxwork. 



In the sketches several minor details are purposely omitted 

 and only sufficient particulars shown to explain the method of 

 working. The under side of the upper centre plate which carries 

 the cylinder castings and smoke-box end of boiler is cup-shaped, 

 and fits into an annular groove or channel in the lower centre 

 plate, which is suspended from the framework of the truck by 

 the four swinging links. Practically the entire carrying and 

 swivelling work of the bogie truck is effected by the annular- 

 groove casting moving round the cup-shaped casting, and the 

 centre pin is merely passed down through each to guard against 

 the risk of the one lifting out of the other from sudden shock or 

 derailment. 



The lateral movement of the truck is obtained by means of 

 the four swing-links. When the engine is on the straight road 

 the centre line of the bogie is on the centre line of the engine, 

 and the links hang in the positions shown on the sketch, inclined 



