MACHINERY. 



machine proceeds in an uniform manner : flill the box is a 

 very ufeful provilioii in cafe of any accident happening to 

 the machine to flop it, by anv thin;^ gettinj^ into its move- 

 ments : the box then Hips round uitiiout breaiiinjj the works. 

 All machinery, whicli is expofed to th<» chance of great vio- 

 -lence, fliou'd be provided with fomc ecjuivalent contrivance, 

 Avhich permits the movement to (lip when the machine is over- 

 loaded and would otherwife be broken. An inllance of this 

 will be I'een in the Dueuging Eir^inc j fee that article. The 

 fame efTett may be produced by conical wheels fitting into 

 each other, in the manner of a valve and its feat. One of 

 them being fixed to each fpindle, will, when they are jambed 

 into each other, comnmnicatc the motion, b'lt perniits it to 

 flip if overloaded. A very ingenious application of this 

 will be found, in the mortifnig machine of the block machines 

 at Portfmonth (fee MAClllXtRy fir manufailuring Skips' 

 i?/or/-j), and another jndicions application oi it under Lot-- 

 -WOOD Mill. 



Many other contrivances are in ufe for detaching or uniting 

 motions' at pleafure. In cog-wheclr, the fitpports for the 

 gudgeons are fometimes fitted up fo as to be moveable, that 

 the wheels can be feparated to fuch a diitance as to relieve 

 each other's teeth. At other times one of the wheels is fitted 

 on a round part of its axis, and united with it at pleafure 

 by a clutch-box. Thus the wheels are always in motion, but 

 one of them can be detached at pleafure from its axis, on which 

 it flips freely. Bevelled cog-wheels are cafiiy difengaged, 

 •by fuffering the axis of one to move a little endways, and 

 then their teeth are feparated. 



Wheels turned by (traps are readily connected, or call off, 

 by removing the llrap, but this is not cafily done while the 

 wheels are in motion ; though fome dextrous workmen are 

 .able to put on the ftraps when the wheels arc going ; but 

 it is attended with much difficulty, and great danger, if the 

 motion is quick, of catching the fingers in the ftrap. We 

 have known an inllance of a man's arm being torn away at 

 the flioulder, by careleffnefs in perfornnng this operation. 



For difengaging the motion of a Urap, the contrivance 

 called the live and dead pulley is very ingenious : it confitls 

 of two pullies placed clofe together upon any axis which is 

 to receive a circular motion. The endlefs llrap or band, by 

 encompaffing one of ihefe pullies, gives it a conllant rotatory 

 motion. Now one of them being fixed fall upon the fpindle, 

 and the other flipping freely round upon it, gives the means 

 of turning or difconlinuing the motion of the fpindle at 

 pleafure, by flfifting the llrap either upon the live or dead 

 pulley, which, as they are exadly of the fame fize, and 

 clofe to each oiher upon the fpindle, iseafily done. 'I'helive 

 pulley IS that which is fixed to its axis, fo called from its 

 caufing life or motion' to the fpindle, and the machinery 

 appended to it. The dead or idle pulley is that which flips 

 upon its fpindle ; therefore, when the llrap is caufed to run 

 upon it, it turns round without giving any motion to the 

 fpin Jle. This contrivance is extremely well adapted to give 

 motion to fmall machinery, from the fimplicity of its cou- 

 ilruftion, and the facility with which it is put in motion or 

 at reil. It polfefies alfo another great advantage, w'z. it 

 occafions no fudden fhock to the machinery at firll Ibuting, 

 as it does not inllantly communicate to it the lull velocity. 

 To lUullrate this, fuppofethe llrap running lipoii the dead 

 pulley, and the machine therefore at rc!l, the leading fide of 

 the llrap is in general conduced through a notch in a piece 

 of board wliich is fitted in a groove, fo as to have liberty of 

 Hiding in fuch a manner that it may condudl the llrap to 

 work upon either of the pullies ; but this is not necellary 

 nor always attended to, for the perfon who attends the ma- 

 chine may, by the flighteil preflure un the leading iide llrap 



by his hand, caufe it to fliift upon the other pulley ; but as 

 this is not done inllantly, it communicates the motion to the 

 live pulley by degrees ; for at firll fiiifting, it be^'ins upon a 

 very narrow furface of the pulley, which is, therefore, urged 

 into motion, but without violence to the machine, as the llrap 

 at firll flips partially upon the furface of the live pulley, and 

 this, as we have before ilated, caufcs the llrap to endeavour 

 to efcape from the pulley ; but the attendant continues to 

 prcfs the ftrap on the leading fide, and force it to adt upon 

 the live pulley, which having attained its full velocity, and 

 the ftrap no longer (lipping upon it, has no tendency to get 

 olF, uulefs the machine is overloaded, and then it will get 

 off to the dead pulley. The live and dead pulley is very 

 cxtenfively ufed in cotton machinery, and is a very excellent 

 contrivance; the only objedion to it being that the bndi in 

 the centre of the idle pulley is liable to wear Very loofe m 

 a (hort time. It is fcarcely necefiary to add, that the driving 

 wheel for the (Irap of the live and dead pulley mull be as 

 broad on its edge as both the live and dead pulley toge- 

 ther ; indeed, it is generally a lonir cylindrical drum, which 

 receives many llraps for turning different machines. 



A motion is frequently required in machinery, by which 

 a wheel or axis is made to revolve in one diretlion for any 

 required time, and then at plealurc changed, fo as to re- 

 volve in the other diredlion. Various means may be ufcd 

 for efietting this purpofe. The molt common is by means 

 of two equal and fimilar bevelled orcontrate wheels, fituated 

 on the fame axis, and their teeth towards each other. A 

 third bevelled wheel is applied with its axis perpendicular 

 to tli£ former, and its teeth engaging at pleafure with either 

 of the two wheels, which, as they turn the fame way round, 

 and can be made to act at one or other of the fides of the 

 third wheel, fo as to turn it in either diredlion, as it is engaged 

 with either of the two wheels. This movement was applied 

 by Mr. Smeaton to a machine he invented for drawing coals 

 from coal-pits. In this the third wheel was a trundle, and 

 could be, by a lever, made to work in the teeth of either of 

 the cog-wheels which were mounted upon the axis of a 

 water-wheel, and thus turned the trundle either way. at plea- 

 fure, to draw up or let down the balkcts or corves, which 

 were fufpended from a drum upon the axis of the trundle. 

 Some mechanics have conllrudled the contrivance in a dif- 

 ferent manner, by fitting the two wheels upim a circular 

 part of their fpindle, and fuffering them tu turn round freely 

 upon it. Their teeth are a' ways engaged with the teeth of 

 the third wheel, and, therefore, they are always revolving 

 in oppofite dired^ions, and either can at plcalure be con- 

 nedted with the axis by a fliding clutch-box, but which is not 

 long enough to engage both at once. The axis can, by this 

 means, be made to revolve in the direction of either wheel 

 at pleafure, by Hiding the clutch-box towards that whee'. 



We have feen a very ingenious application of the live and 

 dead pulley to this purpole, for a crane in a cotton mill, to 

 take up and down the goods, work-people, &c. It was in- 

 vented by Mr. Henry Strutt, and has been applied in his 

 cotton mills at Belper, Dcrbylhire. In this machine it was 

 necefl'ary to have a motion which could be turned eitlier way 

 at pleafure, to draw up or let down .the ba(l<et ; but the 

 double wheel-work above defcribed was evidently improper, 

 from the fudden jerk it would liave given at the mltant of 

 changing the motion. It was effedled in this manner ; an axis 

 which gave motion to the crane barrel, has two pair of live 

 and dead pullies upon it, and alio a brake wheel to llop the 

 motion, which is fituated between the two pair: an endlefs 

 llrap is condudled to each pair, being turned by a long drum 

 placed parallel to the axis of the pullies, and kept in conllant 

 motion by the mill. One of thefe endlefs llraps is crolied 



between 



