TURNING. 



the fame way round, fo tliat the turner has no need to tak« 

 his tool off the work. 



The centre lathe will turn any kind of work which will 

 admit of being fupported at both ends ; and it is ufed by 

 mill-wrights and iron-founders, for turning mill-fhafts, axles, 

 rollers, and other iron-work. For fuch purpofes, the 

 lathe muft be made exceedingly ftrong, and with nuts and 

 fcrews to fallen the puppets down upon the bed, inftead of 

 wedges ; the reft muft be made in iron, with the requifite 

 adjuftments for placing it clofe to the work, at that part 

 where it is required to be turned. To put the work in mo- 

 tion, the centre pin or point in one of the puppets is made to 

 projeft confiderably, and has a pulley fitted upon it, fo that 

 it can turn freely round upon the pin by means of an endlefs 

 band or ftrap, which communicates the motion from a great 

 wheel. In thefe large lathes for iron-work, the wheel is com- 

 monly turned by horfes, or by a water-mill or ileam-engine. 

 From the pulley a pin projefts in a direftion parallel to the 

 centre pin, and a piece of iron, called a driver, is fcrewed 

 or clamped faft upon the end of the piece of work, fo as to 

 projeft from it fufficiently to be intercepted by the pin 

 which is faftened into the pulley : by this means, the motion 

 of the pulley is communicated to the work. The tools em- 

 ployed for turning iron and other metals are different from 

 thofe ufed for wood, as we fhall afterwards defcribe. 



The fpindle or mandrel lathe will turn hollow or internal 

 work, and is equally well adapted to turn centre work as 

 the centre lathe. In Plate Turning, jig. i. we have given 

 a reprefentation of one of thefe, which is on a very good 

 conftruftion, made by Meflrs. Holtzapfel and Deyerlien : it 

 is put in motion by the foot, fo that the turner has both his 

 hands at liberty to direft the tools. A A are upright legs, 

 to fupport the bed B, which confdts of two pieces or 

 bars of caft-iron, put together, and leaving a fmall crack 

 between them : C D is a caft-iron frame, which is faftened 

 down upon the bed B, and fupports the fpindle or mandrel 

 ab: E is the back puppet, which is ufed to fupport one end 

 of a piece of work, as is (hewn in the figure at G, when the 

 other end is fixed to the end of the mandrel, and turned 

 round by it : the back puppet, E, has a cyhndrical pin ac- 

 curately fitted into it at the upper part, and the end of the 

 pin is formed to a ftiarp conical point, proper to penetrate 

 and fupport the end of the work : this point is called the 

 hack centre. A fcrew e is tapped into the puppet, fo as to 

 prefs on the oppofite end of the pin, and force it towards 

 the work ; and there is likewife a clamp fcrew, E, at the top, 

 to bind or faften the pin into its focket. The back puppet 

 is faftened down upon the bed, by means of a tenon en- 

 tering into the groove, through the bed B, and a fcrew 

 defcends from the tenon quite through the bed, and pro- 

 jeAs beneath it : upon this fcrew a nut g is tapped, and by 

 turning it, the ftioulder of the puppet E is drawn down 

 firmly upon the bed; but when the nut is loofened, the 

 puppet can be flided along the bed to place it at any re- 

 quired diftance from the end of the fpindle, according to 

 the length of the piece of work G. It is neceffary that 

 the point of the back centre fhould in all cafes be precifely 

 in the centre line of the axis of motion of the fpindle a b ; 

 and for this purpofe, the bed muft be made very ftraight, and 

 flat on the upper furface ; the groove through it fhould alfo 

 be perfectly ftraight and parallel, and the tenon at the lower 

 end of the back puppet muft be exaAly fitted to the 

 groove : the frame of the mandrel muft be fo fixed on the 

 bed, that the centre hne of the mandrel will be exaftly 

 parallel to the bed, and to the groove in the bed. 



Mandrels are mounted in different ways, but they are 

 always made of fteel at the parts where they are fupported 



Vol. XXXVI. 



in the collars, which collars fhould be alfo made of fteel, 

 and hardened, fo as to have little friftion. The neck of a 

 mandrel muft be very accurately fitted into the collar, fo as 

 to have no fhake or loofenefs, at the fame time that it can 

 turn round quite freely. 



The neck at one end projefts beyond the collar, and tbie 

 projecting part is formed to a fcrew, for the purpofe of fix- 

 ing the work to it. A variety of pieces, called chucks, are 

 fitted upon this fcrew, and each chuck is adapted to hold a 

 different piece of work : the chucks fcrew up againft a 

 ftioulder on the end of the mandrel, and by the motion of 

 turning round ip the direftion in which the lathe works, the 

 chuck fcrews itfelf faft on againft the ftioulder ; but if the 

 lathe is ftopped, and the chuck is turned in the oppofite 

 direction, it will unfcrew and come off, and a different chuck 

 may be put on. In fome lathes, the neck of the mandrel is 

 perforated, and cut withinfide, with a female fcrew adapted 

 to receive a male fcrew on the chuck : the effeft is juft the 

 fame as the above defcribed. The oppofite end of the 

 mandrel to that on which the chucks are fcrewed, muft be 

 fupported either by a point or in a collar. In general, the 

 mandrel is made with a point at one end ; and the other end, 

 which lias the fcrew to fix the work to it, is formed with a 

 neck, proper to run in the collar, and with a ftioulder on the 

 neck, to ftop the neck from going through the collar. The 

 mandrel reprefented in the drawing has a neck and collar at 

 each end, for a purpofe which will be explained. When the 

 mandrel is made with a pointed end, the point muft be re- 

 ceived in the end of a fcrew tapped through the part D of 

 the frame of the mandrel, juft in the place of the end a 

 of the mandrel. By turning this fcrew, the mandrel can 

 be adjufted to run very correftly in length ; and to pre- 

 vent the fcrew from turning back when the lathe is in 

 motion, a nut is placed on the fcrew, beyond the part 

 d: this caufes fuch a preffure upon the threads of the 

 fcrew, that it is in no danger of turning back, as it would 

 otherwife do with rough work. The mandrel, by this 

 means, runs very fteadily and accurately in its bearings, and 

 it is plain that any piece of work, which is firmly attached to 

 the end of it by means of the fcrew before mentioned, may 

 be turned by a tool held over the reft, in the fame manner as 

 if it were mounted between centres, but with the advantage 

 that it be turned at the end, to make hollow work when 

 required. 



The mandrel is turned round by a band of catgut palling 

 round tlie pulley h, and alfo round the large foot-wheel H, 

 which is made of caft-iron, and fixed on the end of the axis 

 I. This axis is bent in the middle, as in the figure, to form a 

 crank, which crank is united, by an iron link K, to the trea- 

 dle L, on which the workman preffes his foot. This trea- 

 dle is afiixed by three rails to an axis M, on which the treadle 

 moves. The wheel H is of confiderable weight in the rim, 

 and being fixed faft on the axis I, turns round with it : the 

 momentum acquired by the wheel is the power that conti- 

 nues to turn the work while the crank and treadle are rifing, 

 and confequently while the workman exerts no power upon 

 them. 



When the crank has paffed the vertical pofition, and be- 

 gins to defcend, the workman preffeshisfoot upon the treadle, 

 to give the wheel a fufficient impetus to continue its motion 

 until it arrives at the fame pofition again. The length of the 

 iron link K, which connefts the crank with the treadle, muft 

 be fuch, that when the crank is at the loweft pofition, the 

 board L of the treadle, to which the Unk is hooked, ftiould 

 hang about two or three inches from the floor. To put 

 the lathe in motion, the turner gives the wheel a fmall 

 turn with his hands, till the crank rife to the higheft, and 

 3 L paffes 



