TURNING. 



•upon brafs and bell-metal. The cutting edge fhould be 

 ground nearly to the angle which is there reprefented, and 

 the upper fide fliould be direfted nearly to the centre of the 

 .piece ; the edge will then fcrape away fhavings from the 

 metal. The tool has feme tendency to retreat backwards 

 from the work, and muft be held firmly thereto. The edges 

 of tools, applied as fliewn in fg. 39, may be formed to 

 any of the ihapes (hewn in Jigs. 23. and 24. the angle of 

 the cutting edge being in all cafes nearly the fame. 



The graver {Jig. 40. ) is an extremely ufeful tool, and fit 

 for turning any metal or hard wood : it is a fquare bar of fteel, 

 cut off obhquely, and the greateft obliquity of the cutting 

 plane is in the diredion from one angle of the fquare to the 

 oppofite angle. This produces a prominent point on one of 

 the angles, which point is applied to the work in the manner 

 fhewn yajig. 40. and cuts off continuous (havings inftead of 

 fcrapings : this is owing to the direftion of its edge, which 

 is difpofed obliqu?ly to the motion with which the work 

 meets the edge in its rotation. The turner (hould be pro- 

 vided with gravers of all dimenfions. 



Ftg. 37. is the aftion of what is called a /i.'f/ tool for 

 turning wrought iron or copper : the edge of this is applied 

 nearly in a tangent to the work, on the fame principle as the 

 chiffel is applied to cut wood. The heel of the tool is placed 

 upon the reft, and being juft. oppofite to the edge on which 

 the preffure or drift of the work lies, the tool cannot 

 efcape from its work, although the preffure upon it is very 

 great, fo much fo, that it would be impoffible to keep the 

 tool to its work, if it were held upon the reft, as in the cafe of 

 the wood chiffel, merely by the lateral friction on the reft. 

 The handle of the heel tool is long, and is held inclined up- 

 wards, fo that the workman can reft the end of it oa his 

 fhoulder, whilft he holds it very firmly down on his {houlder 

 and on the reft with both hands. This firm pofition is 

 very neceffary, becaufe the heel tool is liable to draw 

 deep into the work, and take away too large a chip. 

 This tool w'iU cut away thicker chips than any other, being 

 ■what the workmen term a greedy tool. The requifite height 

 of the reft, to make the edge of the tool a tangent to the 

 proper point, is a matter of importance, and requires the at- 

 tention of the workman, who can only leain the manage- 

 ment of this tool by experience. It is not well adapted 

 for finilhing work with accuracy, but is very expeditious in 

 roughing out wrought iron : it generates fo much heat in 

 ■working, that it is neceffary to keep it conftantly wet ; and 

 in large lathes, a conftant ftream of water is made to fall on 

 the edge at the place where it is cutting. The graver and 

 all other tools work wrought iron and fteel to the greateft 

 advantage when wetted. 



Fig. 39. is the tool ufed for turning caft-iron ; this fub- 

 ftance muft be fcraped away, and it is plain from the figure, 

 that the cutting edge is prefented very nearly in the fame 

 manner, with refpeft to the work, as in_^^. 39 ; but from the 

 hardnefs of caft-iron, it requires a very confiderable force to 

 prefs the edge againft the work, and it would be imprafti- 

 cable to hold it up effeftually on the plan of^». 39 ; hence 

 the tool in_^^. 38. is bent at the end, and is lodged over the 

 edge of the reft, in the manner of a lever ; the handle is preffed 

 down at the extremity, and lifts up the edge againft the work 

 with very great force. The workman muft bear on the han- 

 dle of this tool with the requifite preffure ; and iu large work, 

 fuch as cannon and raill-fhafts, he ufually feats himlelf upon 

 the end of tue tool, which is made very long in the handle. 



Different fubftances require different velocities of motion 

 to cut with the greateft advantage. Wood can fcarcely be 

 made to move too quick ; and it is always preferable to take 

 J Very thin chip, and move as quick as poffible, than to move 



flowly, and compenfate for the lofs of time by cutting 

 deep. Brafs and bell-metal may be moved very quick, 

 but not with half the velocity of wood. Wrought iron and 

 copper muft be turned more flowly, and the tool muft be 

 kept wet. Steel ftiould go rather flower than wrought iron, 

 for it is liable to have hard veins in it, which the workmen J 

 call pins : thefe will be cut through if the work moves ^ 

 flowly, but with a quick motion they will deftroy the edge 

 of the tool : this makes fome workmen think that the pins 

 are aftually formed, or that they become hard during the J 

 operation of turning, if too great a velocity is ufed. Caft- \ 

 iron muft move very flowly, indeed it can fcarcely turn too 

 flowly, ani the tool applied as at f.g. 38. will cut a thick 

 chip. 



To obtain thefe different degrees of velocity, the foot- 

 wheel of the lathe ^/[f. i. is made with feveral grooves of dif- 

 ferent diameters, and the mandrel pulley h has alfo different 

 fizes. A band can be applied upon any of thefe grooves at 

 pleafure, and the workman finds by experience what velo- 

 city is beft for different kinds of work. 



The moft experienced workmen prefer a centre lathe to a 

 mandrel lathe, when they have to turn accurate iron-work, 

 whicli will admit of being poifed between centres ; and it is 

 obvious, that the revolving motion of the centre point at the 

 end of the mandrel is of no ufe ; and if the point ftiould be the 

 leaft out of the centre line, or if the mandrel has any ftiake 

 in its collar, the work would not be turned truly. But in 

 a centre lathe, wliere both pouits are fixed immoveably, or, 

 as the workmen fay, with dead centres, this cannot happen ; 

 and if the work is fcrewed up tight between the centres, fo 

 that there is no ftiake, the centre points at the ends of the 

 work muft be precifely in the centre line of the work. 



The manner of giving motion to a piece of work in the 

 centre lathe is, as we have before defcribed, by a loofe pulley 

 fitted on the centre pin, and from this pulley a pin projedls 

 in a direftion parallel to the centre line, fo that it comes 

 exaftly in the place of the claw e {Jig. 8. ), and turns the driver 

 round when tne pulley is put in motion by the band, either 

 from a foot-wheel or hand-wheel. 



When the mandrel lathe is ufed for centre work, the 

 centre of the chuck muft be turned very exattly, fo that it 

 does not vary in the leaft from the fame pofition when it 

 turns round ; and in all cafes, the mandrel muft be fitted with 

 the moft fcrupulous accuracy into its collar, fo that there 

 will be no ftiake ; for unlefs this is the cafe, the lathe will 

 not turn chuck-work with any accuracy. 



Meffrs. Holtzapfel and Deyerlien make very excellent 

 lathes on th^ plan reprefented m Jig. i. The bed and. the 

 puppets are made of caft-iron, and very correftly fitted, 

 fuch lathes poifefs great ftrength : fome of them are fitted 

 up, as in the figure, w ith a pattern fcrew at the end a of the 

 mandrel, for the convenience of cutting fcrews on work. 

 For this purpofe, the mandrel is fitted in a collar at each end, 

 and the necks are cylindrical, fo as to admit of the mandrel 

 moving endways at the fame time that it turns round. On 

 the extreme endof the mandrel, beyond the collar D, a pattern 

 fcrew is fixed, which has the diftance of its threads corre- 

 fponding with the fcrew that is defired to be cut upon the 

 work, which is fixed in the lathe by a chuck : a piece of 

 brafs, n, is provided, which is cut with threads adapted to the 

 pattern fcrew, and which can, by turning a fcrevy, be drawn 

 up againft the pattern fcrew, fo as to work in its threads ; 

 and in this ftate the mandrel, at the fame time that it turns 

 round, will move endways in its collars with a fcrewing mo- 

 tion ; and in cor;fequence, a pointed tool being prefented to 

 the work, and held faft on the reft, will cut a fpiral groove or 

 fcrew upon its circumference. This contrivance is more 



fully 



