MO 



APPLIED MECHANICS. 



[STRAPS BUSHES CRANK. 



machinery, it U often plit open at the inudl end, and 

 wedge Q ia driven in to spread it laterally. 



Fig. 177. 



The fork -end (Fig. 178) is made by forming the end 

 of the connecting-rod like afork, fitting it with gun- 

 Fig. 178. 



metal bushes, and tightening them by means of a gib 

 ami key. 

 The bushed eye (Fig. 179) is formed by shaping the 



Fig. 179. 



end of the rod into an oyp, in which gun-metal bushel 

 are fitted, capable of bein,- tightened by a key pawing 

 through a iilot in the rod, and bearing against the lower 

 both, which is notched to receive it 



line* the even arc made as represented in Fig. 

 /80. Th end of the rod A U Hproad out to form a flat 



face, on 



which are 



Fig. ISO. 



fitted two brasses made with a 

 hole to fit the pin, and 

 secured by means of bolts 

 and nuts D, J 

 through holes in the end of 

 the rod, and in the brasses 

 fitted accurately to receive 

 them. 



Such are the modes prin- 

 cipally used in forming the 

 eyet of connecting-rods, or 

 of any joints through which 

 considerable strain has to be 

 communicated. 



The crank A (Fig 181), is 

 made, sometimes, of cast- 

 iron for stationary engines, 

 but, generally, for marine en- 

 gines, of wrought iron, having 

 a hole fitted to B the round end of the shaft, on which 

 it is fixed, and prevented from turning by a key C, or 

 tapered piece of iron, driven tightly into a slit, formed 



Fig. 181. 



partly in the crank and partly in the shaft. Generally, 

 the round hole in the crank is made slightly smaller in 

 diameter than the round end of the shaft ; the crank is 

 heated so as to expand it, and permit it to be driven on 

 the shaft ; and as it cools it tends to contract, and there- 

 by becomes very firmly bound on to the shaft, the end of 

 which is riveted or hammered over the hole. The 

 crank-pin D is made to fit truly into a hole in the crank, 

 in which it is sometimes secured by a key or pin driven 

 through it transversely. The distance E F, between the 

 centre line or axis of the shaft and that of the pin, is 

 called the throw of the crank, and it is exactly half the 

 length of the stroke of the piston. For locomotive engines, 

 and, indeed, for many of the largest marine engines, 

 where double cranks are required, it is usual to forge 

 both cranks and the shaft in one piece, as indicated 

 in Fig. 182. Ity this means great strength and sim- 

 plicity are secured, and all the risk of the loosening of 

 parts, put together by keys or otherwise, is avoided. 

 Fig. 182. 



ECCENTRIC. At, by means of a crank, the reci- 

 procating motion of a piston is converted into a conti- 

 nuous rotary motion of the shaft, so the continuous re- 

 volution of the shaft may, 1>v im-nus <>f a cran*. I on- 

 verted into a nviiirocatiiiL,' movement for the. slide or 

 feed-pump ; but for this pui-]x>se, instead of a crank, an 

 eccentric is goaenJlv employed. It consists of a circular 

 disc A, (Fig. 183), having n hole 15, nut. in i 

 through which the shaft passes. Round (lie disr 'n fitted 

 a ring C, generally made in halves, secured to each other 

 by bolt* and nuts at 1) ; and to one side of the ring U 



