TURNING. 



being taken by one end of the callipers, the oppofite end will 

 be readily opened to the requifite dimenfions for a foHd to fill 

 fuch hollow. 



Fig. 34. is a gauge for meafuring the depth of hollow 

 work. A is a ruler, through which is a focket to receive 

 another ruler B ; and a clamp-fcrew is fitted through the 

 fide of the focket, to hold the ruler, B, fail in the focket. 

 The edge of the ruler. A, is applied to the end of the 

 work, and the other ruler is then Aided through its focket, 

 until the end of B touches the bottom of the cavity ; and in 

 this ftate, the clamp-fcrew being fattened, the gauge may 

 be applied to the piece of work in the lathe, to afcertain if 

 the cavity is turned out to the required depth. 



Fig. 6. is a chuck for turning wood when it is a long 

 piece, which will admit of being fupported at both ends, or 

 between centres, as it is called. The chuck has a fcrew 

 within the part a, to fix to the mandrel, and the other end 

 is of fteel, with a pin b in the centre ; and on each fide of 

 the pin is a (harp edge r, like a chifiel, the line of the edge 

 pointing to the centre of the pin. When a piece of wood 

 is mounted between the points of this centre pin and of the 

 back centre, as we have before defcribed, if the back centre 

 fcrew is turned, it will force the piece of work againft the 

 mandrel and the pin i, and the edges c will penetrate into the 

 oppofite end of the wood ; in this cafe, the motion of the 

 mandrel and chuck « will be communicated to the wood, to 

 turn it round. The centre pin b is made to projeA beyond 

 the edges c, and by this means the work may be removed 

 from the lathe, and put in again if required, becaufe the 

 centre pin will enter again into the fame hole in the end of 

 the work, and reftore the work to its original pofition. 



Fig. 7. is a chuck for the fame purpofe, but it is made 

 with a flat circle of brafs, and three pins, c, are fixed in it 

 inftead of the edges c, c. This kind of chuck is {hewn in ufe 

 in_y^. I, to turn a pillar for a baluftrade. 



When a piece of metal work is to be turned between 

 centres, the edges or points of the lail chucks cannot be 

 made to penetrate the end of the piece, and therefore a 

 fmall chuck, b, {Jigs. 14. and 15.) isfcrewed to the mandrel : 

 in the end of this chuck, at b, is a hole, which is made fquare 

 withinfide, and the work has a fquare filed at one end to fit the 

 hole. The other end of the work is fupported by the back 

 centre, a fmall hole being made in the end to receive its 

 point ; or if the end of the work is fharp-pointed, the 

 back centre pin is drawn out of its focket, and turned end 

 for end ; the end of the pin oppofite to the point has a 

 fmall centre hole for the reception of fuch pointed work. 

 Iron and fteel work may be turned very conveniently by 

 means of a fquare, but not very accurately ; and after the 

 work has been taken out of the lathe, and the fquare cut off, 

 if it be required to turn the work again in the lathe, it is 

 very difficult to find the true centre. 



All works requiring great accuracy, as arbors, fcrews, 

 axles, fpindles, &c. are turned between centre points, thus : 

 a chuck (fg. 8. ) is fcrewed to the mandrel by the fcrew m 

 the part a, a fteel centre point b being formed at the end of it. 

 The point is turned very truly, to be exadly in the centre 

 line of the mandrel. The work is mounted between this 

 point and the point of the back centre ; and to communicate 

 the motion of the mandrel to the work, a driver {/^. 9-) '» 

 fcrewed faft on that end of the work neareft the chuck. 

 The driver is an iron ring, with a fcrew d tapped through 

 one fide of it, to pinch the work fo faft as to prevent tlie 

 driver flipping round upon the work ; and on the fide oppo- 

 fite to the ring is a projefting tail/. . 



The chuck (/^. 8. ) has a fteel claw k e fitted through it, 

 and faltened by a fcrew : the end of the claw is bent at e paral- 



lei to the direftion of the mandrel, fo that the end of it will 

 catch the tail/of the driver, and turn it round, together with 

 the work on which the driver is fixed. 



The ftem k of the claw Aides in and out of the focket, 

 through the chuck, in order to remove the claw e to a 

 greater or lefs diftance from the centre point b, and adapt 

 the chuck to operate upon diff'erent fized drivers, for deli- 

 cate or large work. This is the moft accurate method of 

 turning iron work in a mandrel lathe, becaufe the centre 

 points at the ends of the piece are preferved. When one 

 end of the work is finifhed, the driver may be ftiifted to the 

 other end. Such work may at any time be mounted again 

 upon its original centre points, in any kind of lathe, to turn 

 wheels, collets, &:c. which may be fitted upon it. 



The form of the driver is (hewn mjig. 30. In order to 

 make it fit different fizes, the fide of the ring oppofite to 

 the fcrew d is made angular, and the point of the fcrew 

 forces the work into the angular part. 



This driver may be fixed on cither end of the work, 

 whilft the other end is turning ; but when it is neceffary to 

 fix the driver on that part of the work which is finifhed, the 

 end of the fcrew d is apt to pinch and bruife it ; it is there- 

 fore proper to interpofe a piece of iron between the point 

 of the fcrew and the work. But it is better to ufe the driver 

 fhewn 'in Jig. 31: it is compofcd of two bars of iron, united 

 by two fcrews paffing through one bar and tapped into the 

 other : both bars are fomewhat hollowed out in the middle, 

 that they may encompafs the work. If this (hould be found 

 to injure the work, a piece of fheet-lead wrapped round it 

 before the driver is put on will prevent it from damaging 

 the work ; and if the fcrews of the driver are drawn very 

 tight, it will carry the work about with fufficient force to 

 bear turning. 



When a piece of iron or fteel work is to be turned, the 

 centre points at the ends muft be found with great precifion 

 before it is turned, becaufe it is difhcult to cut away great 

 protuberances in metal. The centres are firft found by 

 the compafles, and marks are flightly punched in the ends 

 by a conical-pointed punch. The workman now places the 

 work in the lathe, between the points of the mandrel and 

 that of the back centre, but without fixing any driver on 

 the work ; he then fcrews up the centres, fo as to hold the 

 work juft tight enough to prevent its falhng down. In this 

 ftate, by turning it round with one hand, while he holds a 

 piece of chalk againft it with the other, he afcertains 

 whether it is pitched nearly concentric on the points ; and if 

 it varies much at any one point, he turns back the fcrew to 

 take out the work, and punches new centre points, or alters 

 the old ones, taking care to move them nearer to that fide 

 which appeared to projeft fartheft in revolving, and was of 

 courfe marked by the chalk. 



When he has, by repeated trials, found the true centre, 

 he fcrews up the centre point fo hard, that it may eftec- 

 tually mark the end of the work, by forcing the points to 

 the bottom of the marks punched ; then taking the work. 

 out of the lathe, he drills holes in the ends, at the places 

 which the centre points have marked, and to fuch a depth, 

 that the points of the lathe will not re.ich the bottom. 

 When the work is again returned into the lathe, it will run 

 very nearly concentric, and the driver being fcrewed faft on 

 either end of the work, as is moft convenient, the work wlU 

 be turned round by the clutch projcamg from the chuck. 



The work is now ready for turning, which is done by dit- 

 ferent tools, and applied in a very different manner from 

 the chifl"els and gouges for turning wood. Figs. 37- to 40- 

 are different examples of the manner of turning metals: a 

 tool applied in the manner oi fg. 39. operates very well 



