the art of shaping wood, metal, and other hard substances, into forms with a circular or oval outline, by means of appropriate tools, and a machine called a lathe. The art of turning is very ancient. The potter's wheel is a lathe, with a vertical axis, used for turning, or shaping with the fingers articles of pottery. This is referred to in the Old Testament, and is also mentioned by several of the writers of antiquity.

Turning is one of the most important of the useful arts. Almost all solid objects in which the circle or any of its modifications exists are produced by the lathe. The operation of turning is also as simple as it is useful. The work required to be shaped is made to revolve in the lathe with a circular motion about a fixed line or axis, and the surface is worked to the required form by means of edge-tools, presented to it by hand or held by means of a fixed rest. As the projecting parts of the work are brought up against the cutting-edge they are removed, so that the outer surface remains at an equal distance from the axis of motion, and thus has a circular figure. There is generally but one axis or centre line of the work, but there may be two, in different parts or in different directions. In such a case, however, the work must be turned at two or more successive operations. There are also cases in which the axis is made moveable as the work rotates, as in oval and rose-engine turning. The work may also be turned hollow, or inside as well as out. For outside work, the lathe is furnished with two points for supporting the work at each end, and at the same time allowing it to rotate freely. There is also a contrivance for turning the work round, and a rest for supporting the tool. For hollow or inside work, the work is fixed at one end only, and that is to the extremity of a spindle or mandrel, which, on spinning round, carries the work with it, while the tool applied to the free end hollows it out. Such a lathe is called a spindle, mandrel, or chuck lathe, to distinguish it from the centre lathe, in which the work is supported at both ends. Lathes are also named according to the modes of setting them in motion; such as the pole-lathe, the hand-wheel-lathe, the foot-lathe, and the power-lathe; in the last case, horse-power, water, or steam is used. The wooden lathes used by turners in wood are called bed-lathes; while the iron lathes used for turning the best work in metal are called bar-lathes. The turn-benches and turns used by watchmakers are small centre lathes made of metal.

The word lathe is derived from a very simple form of the machine, in which a string or catgut is fastened to a treadle, and, passing two or three times round the work, is fastened to the end of an elastic pole or lath, fixed to the ceiling over the head of the workman. Hence the machine was called the pole-lath, or simply lath or lathe. It is evident that, on pressing down the treadle, while a gouge or chisel is held on the rest, with the edge brought up to the work, the work will spin round, and thus be cut to a circular form. The man then releases the treadle, and the elasticity of the pole draws it up and turns the work back, during which the tool cannot of course operate, for it can only cut while the treadle is being pressed down. Such a Turning lathe is used for turning the legs of stools, chairs, tables, hand-rails, bobbins, &c., in soft wood. It is more usual, however, to put the work in motion by means of a heavy wheel, worked by a crank and treadle, with an endless cord working in a groove in the circumference of the wheel, and after crossing like a figure of eight, passing over a small pulley attached to the work. The work is thus made to spin round rapidly in one direction with continuous action of the tool.

The puppets, or short-posts which rise from the horizontal surface or bed of the lathe, and which are used for holding the centres to which the work is attached, are secured to the bed by means of cross wedges. For turning heavy work, such as ironfounders' or millwrights', the puppets are secured to the bed by means of nuts and screws; and the centre-pin of one puppet is made to project so as carry a pulley which, by means of an endless band, sets the work in motion. A pin projects from the pulley in a direction parallel to the centre-pin, and a piece of iron called a driver is fastened to the end of the work, so as to meet the pin attached to the pulley, and thus impart motion to the work.

The spindle or mandrel-lathe usually consists of uprights of oak or mahogany, supporting a bed formed of two bars of iron with a space between. Lathes formed entirely of metal are subject to an unpleasant elastic tremor. The back puppet, which supports one end of the work, can be moved along the bed, and fastened to suit the length of the work; it also carries a conical point or back centre, which penetrates and supports the work, and this having been adjusted by means of a screw, can be secured by a clamp. The mandrel must be nicely fitted, so that its centre line may be parallel with the bed, and the centre line of the spindle must exactly coincide with the point of the back centre. The neck of the mandrel must be well fitted into its collar, so as to turn smoothly; and the projecting part must carry a screw for holding the work or the various chucks which serve the same purpose. The other end of the mandrel is supported by a point or in a collar, and the mandrel itself is turned by a catgut band passing round a pulley, and a large iron foot-wheel attached to a crank-axis. The treadle is fixed by three rails to an axis on which it moves, and is united by means of an iron link to the crank. The rest for supporting the tools is fixed to the bed of the lathe by a forked foot and a screw-boil, so that it can be moved to and from the centre of the work, and be adjusted to the required diameter of the work; and by means of a pin and socket, it can also be adjusted as to height. For turning cones, the edge of the rest is inclined to the axis of the work; and for ornamenting balls and other round objects, a circular rest is used.

The turner uses a variety of gouges and chisels, the former for roughing out the work, the latter for smoothing it and bringing it to form. The gouge is made nearly half round to an edge, with the two ends sloped off, so that there may be no corners to catch in rough wood. The blade is a good deal inclined, so that the bevel or outside of the edge may form nearly a tangent to the surface of the work, while the cutting edge is over the level of the centre. The chisels are usually bevelled on either side; or the line of the edge may be inclined to the direction of the blade, or be rounded, or made with angular points. In using the chisel, the rest is raised above the centre of the work, and the line of the cutting edge is made oblique to the axis of the cylinder, to prevent the chisel from running into the work. In order to regulate the dimensions of his work, the turner uses callipers and gauges, and various chucks, also milling tools, or small wheels on which a pattern is cut; so that when pushed close up to the work, the pattern is impressed by a few turns of the lathe. When the turning is finished, and the ends of the work are made flat, it is polished with shark's skin, or Dutch rushes for soft woods, with pumice-stone and chalk for works in ivory and horn; while the metals are polished with tripoli and putty powder.

There is an immense mass of details connected with plain and ornamental turning, which in a regular treatise would require to be illustrated by numerous engravings; but which can be only just glanced at here. The various arrangements of different kinds of lathe can only be understood by means of diagrams; while the very numerous forms of chuck, the modes of mounting the work, and the details of ornamental turning, require a similar treatment. We may, however, notice a few particulars, such as the velocity of the lathe required for the particular work in hand; thus wood should move as quickly as possible, and the shavings should be thin; brass and bell metal quickly, but with less than half the velocity of wood; wrought-iron and copper must move more slowly, and the tool be kept cool by water trickling on it; steel must be moved still more slowly, and cast-iron the slowest of all. Screws are usually cut by means of a pattern attached to the end of the mandrel, so as to give it a screwing motion endways in its collars, while a cutting tool held to the work in one position will cut a spiral channel or screw upon it. The screws may be less accurately cut flying, as it is called; in which case a screw-cutting tool is applied to the work, and moved along endways while the work rotates. With respect to chucks, the concentric or common chuck produces circular work, while the lines which form the circles may be enlarged or diminished by varying the distance of the tool. By means of the eccentric chuck the patterns are circular, but the centre of the work can be shifted as required. Oval or elliptical figures are designed by the oval or elliptic chuck; the geometric and compound eccentric chucks produce geometric and curved designs, while curious intricate patterns are produced by the oblique and epicycloidal chucks; and there is the straight-line chuck, which executes its work in straight lines. Skilful turners pride themselves as much on difficulty of execution as on the delicacy and elegance of the result; and amateurs in general value turned works in proportion as they are opposed to the circular figure. The best lathes are furnished with an overhead motion, which gives motion to the tool, while the work remains fixed. The eccentric cutter, so much used by the ivory turner, is used in this way. Rose-engine turning produces those peculiar patterns called rosettes by the French, whence the term rose-engine. This kind of work requires a particular adjustment of the lathe, and the use of special chucks. In this lathe, the centre of the circle in which the work revolves is not a fixed point, as in the common lathe, but is made to oscillate with a slight motion while the work is revolving upon it, the tool remaining fixed, so that the figure will be out of round, or deviate from the circular figure as much and as often as motion is imparted to the centre. The work is fixed in a chuck at the end of the mandrel, and the tool is held by a slide rest; while the oscillating motion of the mandrel is produced by means of metal rosettes or wheels, with the edges indented and curved, so that, as the mandrel revolves, the waving line of the rosette adjusts itself to a roller, which produces the oscillating motion of the mandrel and of the frame which contains it. There is also a strong spring, which restores the mandrel to a central or vertical position when disturbed therefrom by an indentation in the rose. The mandrel may contain a large number of these rosettes of different patterns, so as to vary the work as it proceeds. In what is called the pumping movement of the rose-lathe, the mandrel is made to move endways on its bearings. By this motion waved lines can be cut upon the surface of a cylinder in the direction of its length. The rose-engine is not moved Tarpon with the foot, but by means of a hand-winch. With the straight line chuck the rose-engine patterns follow a straight instead of a circular direction. The slide-rest for holding the tool and regulating its motions by means of screw adjustments is a most valuable adjunct to every lathe. Indeed it is scarcely possible to over-estimate the signal services which this unpretending piece of apparatus has conferred on machinery; for, instead of the varying and uncertain action of the human hand and arm in applying the tool to the work, we have here an iron hand which never tires, and which, when once set right, will continue to work with accuracy.

(c.t.)