APPLIED MECHANICa 



dutch O, having two projections from it* face ; B the 

 driven abaft, the end of which roaU in the hole of O, and 



on which is fitted, by a feather or parallel key, the other 

 half clutch D, having also projections on its face similar 

 Fi. . to those on C. A groove is 



formed in D, and fitted with 

 a ring E, put together in 

 f . halves, and having pins pro- 

 jecting from its opposite sides, 

 which may bo taken hold of 

 by hand or by a lever. The half clutch D being ca- 

 pable of sliding on the shaft B. can, by means of 

 the ring, be pushed in or out of gear with C ; 

 and as the feather prevents it from turning on 

 its shaft, when the projections on it are in. 

 serted between those in the other half clutch, 

 the shaft B is caused to revolve by the rotation 

 of A. Sometimes, when it is desired that the 

 train passing through any shaft shall be limit- 

 ed, recourse is had to friction-dutches. A very 

 common mode of forming a friction-coupling is 

 to key on one length of shaft, a boss with a co- 

 nical hole bored in its face, and on the other 

 to fit by a feather, a conical boss fitting nicely 

 into the conical hole. When the one is pressed 

 into the other, the friction of the conical sur- 

 faces causes them to revolve together ; but should 

 an excessive resistance be opposed to the rota- 

 tion of the driven shaft, the friction of the sur- 

 face* proves insufficient to overcome it, and the 



Fig. 217. 



in the same straight line, are to be eoupled, recourse is 

 had to a universal joint. On each of the two shafts A 

 and B (Fig. 218) is keyed a fork, 

 in <ho ends of which, at C, D, 

 E and F, are pivoted the ends 

 of a cross O, so as to permit its 

 partial rotation on either of its 

 two axes C D or F E. On A 

 being caused to revolve, the cross 

 is carried with it round its centre 

 O, and its ends E F also rotate 

 round the same centre, giving 

 rotary motion to the other fork 

 and shaft B, the pivoting of the 

 cross permitting it to accommo- 

 date its position to the varying 

 obliquity of the forks during 

 their rotation. 



When two shafts are not quite 

 in the same straight line, but 

 nearly so, they may be coupled by cranks. The 

 shaft A (Fig. 219) has a crank C and pin keyed on 

 to it, and the shaft B has also a crank D, with a slot cut 

 in it to receive the crank-pin of C. The pin must be 

 sufficiently long to allow for the departure of the two 

 cranks from each other by obliquity of position (as indi- 

 cated by the dotted lines representing them at the oppo- 

 site point of their revolution) ; and the length of tho 

 slot must be such as to allow for the difference of level 

 Fig. sis. 



of the two shafts. 



PLUMMER-BLOCKS. Tho hearing in which shafts 

 revolve, are technically called pillow-blocks or plummer- 

 Kg. 219. 



tone on th.> Driving nhaft slips round that on tho other 

 without <lnviiiK it. 



'. .KM XT. When two shafU, not 



blacks. Tlify are generally made of two pieces of cant- 

 iron, the base A, and the cap B, lined with gun-metal 

 Intsket 0, each half a cylinder (Fig. 2iM). 

 Tho base is recessed to receive projecting parts of tho 

 cap; and two bolts D, with nuts at tli< u<U, 



pass through holes in both, so as to secure the c.-ip linnly 



