MACHINERY. 



pivot (Rould be fitted, and kept in accurate contaft with the 

 interior furface of its focket or pivot-hole, and this will 

 prefent a fufficicnt accefsof oil, to prevent any other fpindlc, 

 than one of hardened (leel, from burning or heating by 

 the friftion, when in rapid motion ; and the expanfion oc- 

 cafior:ed by this heat increafes the prefTure and the friftion, 

 till the pivot becomes fixed in its focket, and will rather 

 twift off than turn round in it. The fpindle for a turning 

 lathe mull always he of hard fteel ; and even then, a failure 

 of the fupply of oil for a moment, will caufe it to burn into 

 the collar. Circular faw-fpindles are frequently burnt in 

 tht- fame manner ; their motion being very quick. 



The bell form of a gudgeon or pivot for a fpindle, is that 

 of a cylinder, with a flat fhoulder, to prevent it from fliift- 

 ing i'.s pofition endways. This form will bear mofl fairly 

 and lleadily ; but it is neceffary that the focket, or brafs 

 •which contains the pivot, fhould be made in two halves, and 

 put together with fcrevs, that the halves may be fcrewcd 

 clofcr as the focket enlarges by wearing : but as this is only 

 an imperfect method, becaufe the pivot can never fit accu- 

 rately after having been worn, a conical form is ufed for the 

 pivots of axles requiring great accuracv, as thefe may be 

 always made to fill their focktt.i, by prefTing the cone farther 

 into ks fncket. The cone is ufed in many turning lathes, 

 whil'l others are made very nearly cylindrical, with a 

 fhoulder ; and as the collar is of hard fteel, they do not 

 wear in any fenfible degree. Their advantage over the cone 

 is, that they have no drift endways upon the oppofite 

 centre, as the cone has; though tliis is fo (light in an acute 

 cone, as to be of no importance in fnall machinery. In 

 heavy work-", fuch as the gudgeons of water-wheels, a 

 ■cinical figure would be highly improper, and has no advan- 

 tage to. recommend it ; a=: fuch gudgeons feldom have a:iy 

 brafs fcrewed down over them, their own weight being fuf- 

 ficicnt to keep them down, and they always fi' true as they 

 wear away. The mod accurate and fimple of a!l piwors is 

 (hat which is fimilar to a piece of wo'k, while turning in a 

 lathe ; the axis having a fmall luile made in each end of it, 

 and the fupports formed by'fharp conical points, received 

 into the ho'es ; and one of them muft be adjuftable by a 

 ferew, to make it aKvavs fit the length of the fpindle. It is 

 ufual to make the conical points on the ends of two fcrews, 

 either of which may then be adjulled. The fame thing may 

 be accompliflv d by making conical points at the ends of the 

 fpindle, and forming the holes for its reception in ends of 

 the two fixed fcrews, which can at all times be fcrewed up 

 as the parts wear. It is the mod perfeft of all methods, but 

 is not adapted to bear any great flrain, becaufe the fcrews 

 will get loofe, and all the objetlions to the conical fpindle 

 apply to it. 



Tlie pivot at the lo.ve'r end of a vertical (haft, which has 

 a great weight to fuftain, as in a heavy horle-wlieel, is v^-ry 

 properly made of a hemifpherieal figure, and received in'o a 

 proper cavity. A cylindrical pivot, having a flat end, is 

 frequently ufed for large and heavy upright axes ; but it is 

 difficult to keep oil fupplied to tliem, as the great weight 

 prefles it out from between the afting furfaces, and the 

 gudgeon burns. To avoid this, fome mechanics make a 

 cleft acrofs the lower face of the gudgeon, exadlly in the 

 manner of a fcrew-head. This getting full of oil, is con- 

 ftantly fupplied to the afting furfaces. 



We have feen an horizontal windmil, having a vertical 

 axis loo feet high, with fails and wheels of immenfe weight, 

 all bearing upon one pivot. This was with the greatefl dif- 

 ficulty kept in order; and it was neceffary to keep a fmall 

 ftream of cold water always running into a pan, which fur- 

 rounded the gudgeon, to keep it cold. This method of 



Vol.. XXI. 



watering, inftead of oiling, a gudgeon is alfo ufed in paper* 

 mills ; but it cannot be recommended as a good method. 



Friftion-rollers are frequently ufed for fupporting gud« 

 geons, and, if made with great care, have the leaft friction 

 which can be conceived ; but they are liable to get out of 

 order, if not made with extreme accuracy. See Mill- 



A great number of machines depend upon reciprocating 

 motions, fuch as pump-milh, faw-mill.<i, &c. Where the 

 fird mover has a circular motion, as a water-wheel, the re- 

 ciprocating movement will be moft conveniently produced 

 by means of a crank ; becaufe it commences the change of 

 motion by degrees, and does not fuddenly urge the parts 

 into motion in a contrary diredlion ; nor fuddenly check the 

 movement again, but effedts both changes without violence. 

 It is proper, in fuch cafes, to regulate the motion of the 

 firft mover by a fly-wheel, ocherwife the refiftance of the 

 work, at the inllant of the change of motion, it fo fmall, 

 that the machine would accelerate in that period, and then 

 be checked agam. The fame may be accomplifhsd by- 

 having feveral of the reciproca'ing movements and thefe a^ 

 alternately, that v.hen one requires the moft power, the 

 others take the lead, fo as to equalize the refidance to the 

 fird mover, and make the motion uniform. All recipro- 

 cating machines labour under great difad vantages, from the 

 circumftance that a great mafs of matter mud be put in 

 motion, and this motion deltroyed again. Thus, in a fingle 

 pump forcing water through a great height of pipes, the 

 column of water is, at every ftroke the pump makes, put in 

 rapid moti in, which is wholly loft during the return of the 

 pump-bucket for another ilrake, when fre(h impetus mnft be 

 given to the water: now by applying a double atling 

 pump, or two or three pumps afiting at intervals, and tlie 

 water regulated by an air-velfel, the m.otion wih b\; very 

 eafy, becaufe the column of water will be in conftant mo- 

 tion throu;h the pipes, and the momentum once giveK to it 

 will continue as long as the machine is at work, inilead of 

 requiring a repetition of it at every ftroke. 



In every machine, the aClion of the moving power ic 

 tran^ferred to the working point, through the parts of the 

 machinery, which are ma'erial, inert, and heavy ; or, to de— 

 fcribe it more accuratelv, before the necefl'ary force can be 

 excited at the working point of the niacliine, the various 

 connefting forces mnft be exerted in the different parts of the 

 machine: and in order that the working point may follow- 

 out the imprefllon already made, all the connecting parts or 

 limbs of the machine mult be moved in difl^erent diredtions, 

 and with different velocities. Force is neceffary for thus 

 changing the ilate of all this matter, and frequently a very 

 confiderab'e force. Time muft alfo elaple before all this 

 can be accomplifhed. This often confumes, and really 

 wades, a great part of the impelHng power. Thus, in a 

 crane worked by men walking in a wheel, it acquires motion 

 by flow degrees ; becaufe, in order to give fiitficient roonx 

 for the adlion of the number of men or cattle that are necef- 

 fary, a very capacious wheel mud be employed, containintr 

 a great quantity of inert matter. Ail of this muft be put \a 

 raoti,)n by a very moderate preponderance of the men: it 

 accelerates flowly, and the load is railed. When it has at- 

 tained the required height, all this matter, now in coufider- 

 able mot:on, mull be dopped. This cann.ot be done in aa 

 inftant, with a jolt, which would be very inconvenient, and 

 even hurtful : it is therefore brought to reft gradually. 

 This alfi) confumes time. Xay, the wiicel mud get a mo- 

 tion in the contrary direction, that tlie load may be lowered 

 into the cart or lighter; and this can onlv be aceompiilhed. 

 by degrees. Then the tackle mift be lowered down agaiii 



S.D for. 



