the mandrel is concave, so as to allow the steel point of the screw, S, to lit closely. R is a rest, which slides along the slit between the two beams of the bed, and may be clamped at any point, and elevated or depressed as is found necessary. The rest is used 1, ILA weirkrnn for lomnur it Lis cutting upon, in order to :Word Itgreater steadiness. G is the right-hand. puppet or movable along the slit in the lied, and capably of bent.; fastened like the rest; its point, I, can be advanced or retired as required by meant of ilia screw, J. C is the spindle, which, being connected with the tr3adle, W, by means of tho rods or chains, E, E, turns the fly or foot wheel, F, and by means of au endless ban 1 connecting the latter with the speed-pulleys. communicates motion to the in tndrel. Tim pulleys on the spindle and mandrel are of different SinS, and so arrange] that when the endless band is placed on the left-hand pulleys. an extremely rapid tuition is communi cated to the mandrel, the motion being reduced more and more as the hand is trans ferred more to the right, till, at the extreme right, the rotatory. motion is lunch slower than that of the spindle. When the foot-lathe is required for e3nter-work, the inner end of the mandrel is furnished with a point similar to I; but when hollow or inside work is to be done, it mast be armed with a screw, as in the figure. In this latter case, certain contrivances, known as chucks, for holding the work, are screwed on to the end of the mandrel. Sonia of these most commonly used are the ,screw-chuck, which shows on its right side a flat circular surface. front the center of which projects a large, coarse, conical screw for holding firmly any large piece of woodea tvork; the holloie clinch; a strong eircular.cup with perpendicular sides, into which one end of the work is firmly fastened by a mallet, or, if too small, by four screws working inward th•oag:i its sides; the of a cylindrical form similar to the last, lint with is square cavity for holding drills, the instrument, and not the work, being- made to rotate in this instancz; and the concentric chuck, It most ingenious piece of mechanism—a fiat plate with two ,slits almost to the center, and in line of a diameter, within which slits works at spindle, with screw-ends carrying- two steel studs, whose heads project through the slits above the surface on the right side; these heads carry two curved pieces.-which serve as clump; to hold the work; and as the spindle-screws are of the same fineness, and with right and left threads, the revolution of the spindle either removes both further from the center, or brings both nearer to it; hence, when the studs are once set at equal dis tances from the =ter, they always remain so, and the work may be removed and repliced without danger of destroying the adjustment. All these chucks are of metal, and are mostly employed for heavy work: turners of wood or ivory preferring. wood chucks, which can be altered as required, and secured by an iron ring round the outside, to prevent splitting. The cutting-tools employed are very various: gouges are used to rough out the work—if soft wood—after which chisels witlt a straight oblique edge are employed: the instruments for harder materials, such as ivory or bone, are smaller than theformer, and have their sharp edges "better backed:" for inside-work, flint are first employed to make an opening, and then cutting-tools of various shapes are employed, Jtecorcling to the form which is wished to be given to the interior surface. To avoid the linperfections in the workmanship arising from unsteadiness of hand in the workman, the slide rest is employed. This valuable addition is furnished with two motions, one toward the work, and the other along, parallel. or at any inclination to it, according as cylindrical or conical figures are required; there is a socket for the chisel. which is firmly held in its place by a screw; and after the slide-rest has been adjusted. the oper ator has only to move the rest forward or sideways, as may be required, the motions being effected by two screws andtwinelies.
The hand-wheel lathe is similar to the former, but so much larger as to require two workmen, one of whom is employed in setting the instrument in motion by turning a wheel, which corresponds to the wheel If' in fig. 1. The poecer-lathe is similarly set in motion by horse, water, or steam power, and is employed for heavy metal-work, as pis ton-rods, iron columns of various kinds, wheels, artillery, etc. This machine (lifters from the foot-lathe chiefly in the substitution of rack-work, and wheels and pinions, for the endless baud, and for manual labor, in the various adjustments of the machine, such as in moving forward the tail-stock. etc.; and in the mandrel being supported by both puppets of the head-stock. In wood-tu•ning, the wood is first prepared by a hatchet and rasp, must be lightly' though firmly pressed against by tic cutting-tool; while metal work must be cleaned Irotn the sand of the mold or scales of the forge, and in turning, requires less care. Soft woods must be made to revolve with great rapidity; very hard woods and brass require much less velocity; wrought iron and copper, still less; steel, a further diminution of speed; and cast iron, the least velocity of ail. After the work has been duly shaped, it requires to be polished; and this is effected while it is still in the lathe and rotating„ by applying shark's skin to wood, poi ice-stone and chalk to ivory toid horn, and emery, tripoli, or putty powder to metals.
Hitherto, we have supposed that the axis of revolution of the work is fixed, and con sequently that all work has been turned so as to present it transverse circular section; but many other forms of section may be easily obtained. The general mode of obtaining these non-circular figures is by screwing on to the mandrel an apparatus, by means of which the work can be thrown out of the center of rotation at regular intervals; bat as_ each different class of form requires a separate kind of apparatus, it is impossible here to describe the operations in detail. One species, however, known as rose-engine turning, and employed for producing involved curvilim al figures, such as appear on bank-notes mud on ornamented gold, silver, or gilt work, is so peculiar and ingenious as to call for more special notice. In tins species, the standards which support the mandrel are no longer fixed at right angles to the bed, but are capable of oscillating hackwa•d or for ward in a plane parallel to the plane of rotation of the mandrel, and are so acted on by a spring that when pushed to one side they are at once restored to then• former position on the pressure being withdrawn. Suppose, then, a metal wheel with its rim waved or indented, fastened concentrically on the mandrel, and the mandrel, pushed aside by a fixed steel point or roller, applied to the rim of the the reaction of the spring against the pressure of the roller will keep the latter in close contact with the waved rim throughout, and will produce a definite oscillatory movement of the mandrel. of the chuck, and the work fastened on it, and consequently—the cutting or graving tool being firmly held by the slide-rest—definite deviations from a circle in the lines marked on the face of the work The wave-rimmed wheel, called a rosette, may be replaced by another, and that by a third, and so on till a. sufficient number of difrereut waved lines are obtained. A number of rosettes are generally strung at once on the mandrel, and the fixed guide is brought into gearing by means of a steel band called a rulibtr, with one rosette after another. Similar concentric curves of greater or less perimeter are by removing the slide-rest from, or bringing it nearer to, the axis of revolution.—For more complete information respecting this most interesting machine, and its many varieties of form and application, sec article " Turning" in the English Cycloptedia, Holtzapffel's Turning and Mechanical Manipulations (Loud. 1847-5'2), and Tuurneur• (Montets-Roret), by Valicourt (Paris, 1858).