MACHINERY. 



everlapped are united witVi this cement, and will be as flexible forcing themfclves into fpaces not exaftly fituated to receive 



as any other part, but fo (Ironij that it will fear to pieces them. The bed way is to make the links in the manner of 



in any part rather than at the joint. A tool for equalizing watch or clock chains, with iron plates, and holes drilled 



the thicknefs and breadth of the (Iraps for belts is described through them at equal diflances, to receive crofs pins upon 



in the Tranfaflions of the Society of Arts, vol. xxviii. which the cogs are to aft. By this means the lengths may 



p. 102, invented by Mr. Aubrey. They will by this means be niade far mure accurately than by bending the iron in the 



■ be rendered very correft, for nothing can be more unpleafant manner of common chain links. 



in machinery than the joint and tiiick places in the endk-fs Mr. Nicholfon has dcfcribed a fpinning-wheel for children, 



ftraps jerking over the riggers, and caufing a violent drift at a charity-fchool, in which a large horizontal wheel, with 



upon the centres every time by the increafed tenfion of the a flip of buff leather glued on its upper furface near the 



•[Jfgp_ outer edge, drove twelve fpindles, at which the lame number 



A mechanic, in calculating any cxtenfive piece of ma- of children fat. 

 chinery which is to depend upon ilraps for the communi- The fpindles had each a fmall roller, likewife faced with 

 cation of its motions, particularly if they are of great leather, and were capable, by an eafy and inilantaneous mo- 

 length to convey their motion ti a coullderable diftance, and tion, of being thrown in contaft wiih the large wheel at 

 have much drain upon them, (liould always confider that pleafure ; each child, therefore, could throw her own part 



fuch machinery will lofe fome of its velocity ; that the of the apparatus into work, or caufe it to flop as often or 



wheels, which are turned by fl raps, will never make quite as long as fhe pleafed. 



To many revolutions as they ought to do from a calculation of The winding bobbins for yarn at the cotton mills operate 



their diameters. This is generally fuppofed to arife from the on the. fame fimp'e and elegant principles, which pofTeffes 



fti-ap flipping, in fome degree, upon the furface of the the advantages of drawing the thread with an equal velocity, 



wheels it paffes over, but we are inclined to fufpeft that it whatever may be the quantity of the bobbins, and cannot 



:.arifes from another caufe which has not been inveltiga'ed, break it. The fame mode of cummunication has been adopted 



- I'iz. the elafticity of the ftrap : for inftance, fuppofe that in large work by Mr. Taylor, of Southampton, in his faw 



the diftance between two wheels conneftcd by a ftrap is 



ten feet, and that the drain upon the drap is fuch as to 



ftre'ch or extend it two inches in that length on the fide 



which bears the drain (called by mechanics the leading fide), 



on the other, or returning fide, there will be no drain, and to make the wheels bear firm agaiiid each other, either by . 



mills. In this the wheels afted upon each other by the con- 

 taft of the end grain of wood indead of cogs. The whole 

 made very little noife and wore very well : it was in ufe 

 nearly twenty years. There is of coufequencea contrivance 



therefore the ftrap will return to its original length. In fuch 

 a cafe the wheel which is driven will lofe in its motion tvro 

 inches in every ten feet, becaufe the ftrap gives out that 

 quantity in leading to the wheel, but takes it up again in 

 .returning, as foon as the drain is removed from it. 



wedges at the focket or by levers. This principle and 

 method of tranfmilting n echanic power certainly deferve 

 attention; particularly as the cudomary mode by means of 

 teeth requii'es much ficill and care in the execution ; and 

 after all wants frequent ivp;iir. We have feen it applied to 



Small machines are fometimes turned by a catgut band, a threfliing machine, a fmall wheel on the threfliing drum 



the ends of which are united by a fmall dcel hook and eye, being applied in contact with the large wheel which gave 



the hook being faftened at one end and the eyes at the other, motion to it, and a preft"ure fufficient to make it turn the 



They are made with tubes, for the reception of the ends of machine was given by loading the focket for the fpindle of 



the band, which are tapped with a fcrew withinfide, and the the drum with a confideiable weight. The fame principle 



band being tapered and fere wed into the tube holds very is capable of communicating motion with great accuracy 



fad. But to prevent it drawing out, a fmall quantity of rofin when no force is required, as will be feen on a pernfal of 



ihould be applied to the end of the band which projefts Mr. Troughton's ingenious method of dividing aftronomical 



throuf'h the tube, and a hot wire being touched to it indruments. See Graduation. 



fmges and hardens the end, that it will never draw out of The conftruftiou of bearings, pivots, gudgeons, or 



the tube. This method is coudantly ufed in fmall lathes, centres, of fpindles, as they are indifferently termed, is a 



and works very neatly. The pullies for a catgut-band diould moft important point; thefe parts being the principal feats 



always be cut with a ftiarp angular groove, for the nception of that friftion which is the dedrudtion of all machinery. 



' of the band, and it fliould not touch the bottom of it, or it Pivots are always made of iron or dcel, both becaufe thefe 



will be liable to flip. For the fame reafon, the pullies are fubftarces are better adapted for rubbing furfaces, and that 



bed made of wood, becaufe metals foon acquire a polifh, their ftrength admits ths pivot being as fmall as pofiibic ; 



which prevent the band holding firmly upon it. The wood the bearing, or bed to receive the gudgeons or pivots, fhould 



fhould be cut with its grain acrofs the direction of the band, be of a fofter metal, as brafs, tin, or zii c, and kept well 



that every part of the circumference may be of a fimilar fuppUed with nil when at Vork. Hirdened detl is a moft 



texture. adir.itjble fubilance for pivots, which have a great drain to 



Endlefs chains are fometimes ufed to communicate mo- bear, and a rapid motion. The bearing cr bed may alfo be 



tion of wheels, and frequently cogs are formed nn the wheels made of the iame material, and is the only inftance where 



to be received into the links of the chains. This method is two bodies, having friftion againll each other, can v.ith 



very prafticable on particular occafions, and tliough it has propriety be made of the fame fubftance : for it is found, 



not advantages to put it in competition with cog-wheels that where iron or foft fteel furfaces are worked with a fric- 



actiiig upon each other when they can be applied, it is in tion againll parts of the fame fubdances, the fridtion and 



many inftances a valuable refource to the engineer to convey abrafion are far greater than when a fofter matenal, ks brals, 



motion to fome didance when it requires to be accurate, and tin, hard wood, ivory, horn, &c. is ufed. The great dif- 



where it would injure the operation of the machine if any ficulty of making hard dtel pivots to fpindles is the only 



motion was loll by the flipping of bands. In making fuch reafon they are nut generally ufed ; but there are fome cafes, 



chains the greated care is neceflary to have all the links in which nothing elfe can be employed; where iteadinels 



precifL-Iy of one length, and the cogs very accurately fitted and accuracy of motion are required, and great velocity at the 



■to them, or a great friftion will be caufed by the cogs fame time. To obtain this accuracy, it it neceflary that tlie 



4 pivot 



