the art of giving circular and other forms to objects, by making them revolve in various manners in a machine called a lathe, and applying cutting instruments so as to produce the form required; or by making the cutting instrument revolve, when the object to be operated upon is fixed.

This art is of great antiquity, and is of immense importance to the practical mechanic. It embraces many varieties, requiring varied machinery for their proper performance, from the simple throwing wheel of the potter to the complicated and nearly automatic slide-lathe, in which, almost independent of manual dexterity, an indefinite number of copies of an article can be produced with unerring accuracy.

There is probably, in the range of mechanical operation, none susceptible of greater accuracy than the art of turning, and there is none which has so much conduced to the improvement of our machinery. The extent of the applications of this art may be learned by the four following conditions, which comprise the most important of its varieties. A knowledge of the manipulations no mere description can convey; and as, in the limits here assigned us, it would be impossible to describe all the varieties of the art, and the machines made use of, we shall content ourselves with such a selection as may appear to us to possess the greatest interest for the general reader.

1st. The article to be turned may be made to revolve round its own axis, and the cutting tool applied to its surface, so as to produce the requisite form, as in simple turning, performed in the ordinary lathe used by cabinet-turners; the more powerful lathe used for turning metal of large diameter; and the self-acting slide-lathe.

2d. The article may remain stationary, while the cutting instrument either merely revolves, or, while revolving, has at the same time some other motion given to it.

3d. The article may be made to move in some curve derived from circular motion, and the cutting tool applied as before.

4th. The article may be made to revolve, and at the same time to have a reciprocating motion in the direction of its axis, the cutting instrument being only applied, however, while the article is either in the course of its forward or backward motion, but its application not continued through both; and all these motions may be more or less combined, thus producing almost infinite variety.

The self-acting slide-lathe being the most perfect of the machines of the first class, we have preferred giving a drawing and description of it, from that the other lathes referred to will be more easily understood than if we had described a less perfect machine. The lathe, when of large size, is generally driven by steam or other power; but when small it is driven by a treadle put in motion by the feet of the workman. The treadle acts on a cranked axle, on which is fixed a fly-wheel; and a band from the fly-wheel passes over the pulley of the mandril or spindle, to which the article to be turned is attached. This is generally the arrangement of the common lathe, which differs from the slide-lathe only in wanting the slide and its moving apparatus, which we are about to describe, and has in place of it a simple rest to work by hand.

The following figures represent the slide-lathe as constructed by Messrs Whitworth & Company of Manchester, and exhibit certain contrivances which have been patented by these gentlemen.

Fig. 1

Fig. 2

Fig. 3

Fig. 1 is a front view; fig. 2 a view of the left-hand end; and fig. 3 a section across the lathe. The same letters refer to he same parts in all the figures. A A is a strong framing, which supports the bed of the lathe B B. At the left-hand extremity of its bed is fixed the head C C, and through steel bushes in the uprights, or puppets as they are termed, the spindle or mandril D works; the projecting right-hand end of the mandril is screwed, so that chucks and other apparatus for holding the work to be turned may be attached to it. One of these, the double driver, will be figured and described afterwards. In brackets projecting backwards from the uprights another spindle E works. One of the rackets and the end of the spindle are seen in fig. 2. On the main spindle D there is a conical pulley F, carrying a pinion on its smaller end; the pulley with its pinion turns on the spindle, but independently of it. To the right of the pulley is a spur-wheel H, fixed on the spindle; to this spur-wheel the pulley can be backed at pleasure, so as to have varied speeds along with it. On the spindle E is a spur-wheel G and a pinion in connection therewith, as shown in the drawing. These are fitted respectively to gear with a spur-wheel and pulley-pinion of the main spindle. Different materials require to pass the cutting tool with different degrees of rapidity, in order to be efficiently operated upon. Cast iron requires to revolve slowly, so that it may come in contact with the cutting tool at the rate of about 100 feet per minute; wrought iron and steel about twice as quick; and brass is better cut at a still higher velocity. Thus, it is required that provision be made for altering the speed, independently of the velocity of the prime mover. It is obvious, too, that the same material may require a change in the speed of the lathe, according to its diameter, that a uniform rate of speed may be maintained by its face. This alteration in the velocity of the spindle or mandril produced by the pulley and wheels we have just described, in the following manner:—When the belt from the prime mover, acting on the pulley F, causes it to revolve, if a slow motion be required, the pinion of the pulley is made to gear with the spur-wheel I of the spindle E; and the motion fixed on the same spindle gear into the spur-wheel H of the main spindle D, causes it to revolve with a motion slow as compared with the speed of the pulley. If a higher velocity be required, the wheel and pinion on the spindle E are put out of gear with the pinion and wheel of the main spindle by sliding the spindle E a little to the left hand, thus locking together the pulley and spur-wheel H, so as to use the main spindle to turn directly by the pulley.

The face of the spur-wheel H has drawn on it a great number of eccentric circles. The circumference of each circle is divided into equal parts, and such numbers are chosen for the division as multiples of the greatest variety of measures; at each division of the circle there is pierced a hole, into which a point is pressed by spring. By means of this apparatus, an object in the lathe can be surface divided into any number of equal parts. On the face of the main spindle is fixed a pinion K, which, by the intervention of the star-wheels and pinion L, drives the spur-wheel fixed on the end of a screw N, which extends along the whole length of the lathe, and is called the leading screw. The ends of the leading screws and main spindle are made accurately of the same size, so that the wheels and pinions may have for different purposes to be fixed on them may be exchangeable. On the right-hand side of the lathe is seen the shifting head or puppet which is capable of being shifted along to any part of the bed, fixed there, and which carries the centre pin. This is adjusted to its work by means of a screw turned by the tool P, and it is fixed by the clamping screw Q. The slide-rest consists of an upper and an under slide; the latter lies across the bed, and is moved along it lengthways by means of the leading screw. The upper slide can move at right angles to the under slide, and carries the cutting tools; the manner in which the tools are moved by the leading screw is, in this lathe, very simple. From the under slide there descends a short vertical slide, carrying on its lower extremity a peculiarly-formed pin a, which is constantly in gear with the leading screw, when the leading screw is in motion and the pinion fixed, the lever serves as a male female screw, and the slide is moved along the bed of the lathe to the right and to the left as the screw may be turned. On the upper end of the vertical spindle there is fixed a mitred wheel b; into this a pinion c works, whose spindle raises the slide, and has a handle d fixed on it. On the slide being reached one or other extremity of the bed of the lathe, it may be carried to the other by reversing the motion of the screw, but more speedily done by turning the handle d which turns the pin a, and so the slide is carried along very rapidly.

The upper slide is moved across the bed of the lathe as follows:—On the end of the vertical spindle there is fixed a mitred wheel c, which works into the mitred wheel of the vertical spindle, is fixed on the end of a shaft f, on whose other end is fixed the wheel g; this gears into another wheel h, fixed on the end of a leading screw, which crosses the main leading screw, and, means of an apparatus similar to that above described, causes the upper slide to move at right angles to the under one. In Turning, fig. 3 the under slide is represented as fixed in its position by means of a clamp, whose handle is seen at k in fig. 1, and the main leading screw is, by means of the pinion a, the mitred wheel b, and the pinion and wheels c, g, h, working the cross leading screw of the upper slide, by which it is moved across the bed of the lathe.

In plain cylindrical turning, the motion of the slide is adjusted in relation to the motion of the article operated upon, that the cutter carried by the slide shall not move over a space greater than the breadth of its point in the time that the article makes one revolution. In screw-turning, the cutter again is made to travel over a space as much greater than the breadth of its point during one revolution of the spindle, as the pitch of the screw requires. The requisite changes in the motion are effected by changing the wheels on the ends of the main spindle and the leading screw.

On the mandril nose there is represented, in fig. 1, what is called a double driver, and we here give the details of an excellent apparatus of this kind, invented by Mr Joseph Clement of London, by which an article can be fixed perfectly true between the centres of the lathe. The figures and description are taken from the Transactions of the Society of Arts of London, vol. xlvii.

"Fig. 4 is a side or edge view of the chuck; and fig. 5 is a face or front view. The same letters refer to the same part in both views.

"a is a circular plate or chuck, on the back of which is formed a boss b; the boss b contains a female screw for screwing it on the nose of the lathe-mandril. On the face of the chuck or plate a, and near the middle, is screwed a conical centre c, on which is supported one end of the thing to be turned, as shown at d in fig. 4. e is a parallel plate in the form of a cross, one side of which is fitted to the face of the chuck a; in the middle of the horizontal arms of the plate e are two oblong holes, bored and tapped by the dotted lines in fig. 5; f g are two screws which pass through the holes f g, and screw into the face of the chuck a; the necks of the screws g are made to fit the holes f in one direction, but the plate e is at liberty to slide to and fro beneath the heads of the screws g, in the contrary direction; there are also thin washers beneath the heads of the screws g, which act as springs, and tend to hold the plate e in the situation wherever it may be slid to; there is also an oblong hole in the middle of the plate e, through which projects the centre c; in the vertical arms of the cross or plate e are six screwed holes; h and i are two studs or drivers, which may be screwed into any of the holes marked j, so as to accommodate the length of the ends of the carrier k. There is a face view of the carrier k, represented in its place (by dotted lines) on the face of the plate, e, fig. 5). The ends of the carrier are acting against the studs h and i.

"Suppose a piece of metal d, to be supported between the centres of the chuck a and the centre of the puppet-head of the lathe, and the carrier k to be fixed on one end of it, as shown in fig. 4; let the plate e (see fig. 5) be slid on the face of the chuck a a little towards the left hand; then the stud h will cause the upper end of the carrier k to move or turn in the same direction upon the centre c. But the stud i, and the lower end of the carrier k, will be moved in contrary directions, and will be separated from each other double the distance that the plate e has slid on the face of the chuck a; therefore, should the plate e be in the above position, and the lathe put in motion, so as to turn the plate a round towards the left hand, the stud or driver h would be the first that would come in contact with the carrier k. But when the turning-tool is applied to the thing to be turned, or any resistance which tends to prevent it from turning round, the carrier k will cause the upper stud h and the plate e, together with the stud i, to be slid towards the end till the stud i comes in contact with the lower end of the carrier k; then the studs or drivers h and i will be acted with equal force against the ends of the carrier k, which will remove the greatest part of the twist or string from the centre c of the chuck a, by which means the slender cylinder may be turned more perfectly than can be done by a single driver. If another stud be screwed into one of the holes opposite the drivers h or i, it will prevent the thing to be turned from overrunning itself, or back-lashing, when it has got a heavy side. The drivers h and i may be made of different lengths, as may be found most convenient."

When it is required to replace in the lathe an article whose centres have been lost, a simple apparatus, called a boring collar, is made use of. It consists of a puppet, capable of being fixed on the bed of the lathe, in the same manner as the puppet O, fig. 1, and as a substitute for it. On the right-hand side of this is fixed, by a bolt through its centre, a disc of cast iron, which has been turned perfectly flat, and which is of as large diameter as the height of the puppet above the bed will admit. On this disc a circle is traced, the highest point of it being exactly level with the centre of the mandril; and all round the circle are bored holes, varying in their dimensions, to suit the different sizes of the objects which require to be centred. The disc moving round on the bolt by which it is attached to the puppet, the floor suitable for the article to be centred is turned uppermost, so as to be on a line with the mandril, and the disc is then fixed in this position by another bolt or pin, which is passed into a hole in the puppet below the centre, through one of another inner series of holes in the plate, which correspond to those above described.

The slide-lathe which we have described is one well adapted for the machinist; but for particular uses, certain modifications are made in the arrangement of these we shall immediately speak. In the mean time we may observe, that a very useful arrangement of the slide-lathe has been made by Mr C. D. May of Edinburgh. In his lathe the slide works, not on the top of the bed, but along its face; it thus can pass from end to end clear of the puppets, and the lathe can at once be converted into an ordinary one to work by hand, by moving the slide to the right-hand extremity of the lathe, clear of the shifting puppet, and applying the ordinary rest to work by hand. This lathe is very neat, is simple in construction, and occupies little space.

The modifications in the slide-rest are as follows: The upper slide, in place of being able to move at right angles only to the lower rest, may have other motions given to it. It may be made to turn round on a centre, and, by an index and graduated arc, may be set at any angle to the axis of the mandril. In this way it is used for turning conical work. The rest may be made, too, to receive cutting instruments, to which circular motion may be given, while the work supported upon remains stationary, as mentioned in the second division of the subject.

In this case a frame is added to the lathe, consisting of two uprights, one at each end, carrying a series of pulleys put in motion by belts from the fly-wheel, and which again, by means of a band, give motion to a pulley fixed on the end of a revolving cutter, carried by the slide. It will at once be seen, that when an article is held in a chuck on the end of the mandril, and turned round, so as, by means of the divided circles on the spur-wheel face, to present any number of sides to the action of the revolving cutter, and when the cutter itself can, by means of the double slides and turning motion, be set in almost any position relative to the work, the variety of uses of which this arrangement is susceptible is almost infinite. Holes may be bored with it radiating from the axis of a cylinder, as for the spokes of a wheel; they may be bored in a straight line, or in a helical line; continuous grooves may be formed in any direction. By using proper cutters, any of the geometrical solids may be formed on the lathe; a very obvious application of this apparatus is to the cutting of the teeth of wheels either denticulate or oblique. Suppose that it is required to cut a wheel of ninety teeth; a circle in the dividing plate on the face of the spur-wheel, containing ninety holes, or any multiple of that number, is selected, and the spring pointer being fixed in the first hole, a proper cutter, fixed on a vertical spindle, is made to act on the wheel, and to cut out the first tooth to the proper depth; it is then withdrawn, and the mandril is turned round until the pointer falls into the second hole of the dividing plate; the cutter is again applied for the second tooth, and so on successively for all of them. In what we have described we have supposed the work to be fixed to the mandril of the lathe, and the cutting instruments attached to the slide; but the case may be reversed, and thence arises a new variety of applications. A circular saw being fixed on the mandril, an article held in the slide-rest may be presented to it, so as to be cut in any plane. Large drills, too, may be carried by the mandril, and the work to be bored fixed to the slide.

To the other varieties of the art the term of ornamental turning or engine-turning is generally applied. Among these are rosette turning, eccentric turning, elliptic turning, epicycloidal turning, and spiral turning. The lathe for the first of these has this peculiarity. The head on the left, in place of being fixed firm on the bed, stands between centres parallel to the spindle at the level of the bed. It is kept in its proper position by the adjusted pressure of four springs, one of which is fixed at each side of the front and back puppet. On the spindles are fixed the rosettes, from which the lathe derives its peculiar motion. These rosettes consist of wheels, discs, or portions of cylinders, having their surface indented in various forms. Fixed parallel to the spindle, but at a lower level, is the bar on which the rubbing apparatus is fixed; the rubber, being placed in contact with one of the rosettes, and incapable of yielding to the inequalities of its surface, forces the spindle on which the rosette is placed, and consequently the articles operated on, to move in various regular curves, as the indentations on the rosette guide them. The rosette may be applied to elliptical turning by using a proper chuck, as described under the head. For vertical waved lines, the spindle is fixed on the head of the spindle, working a rack attached to a vertical slide fixed in the front puppet; to counterbalance the slide, a cord is attached to its top, passed over a pulley above, and attached to a weight at its extremity; thus the pinion is relieved from unnecessary friction.

In eccentric turning, an eccentric chuck is used. This consists of a solid circular plate, which is fixed to the mandril of the lathe. On the face of the plate are fixed two guides, so as to form a dovetailed slide for another plate, which is moved by a screw sunk in a slot in the under plate. On the upper plate is a circular toothed plate, which is capable of being turned round its centre, and is retained in any position by a catch, which falls between its teeth, and is held by a spring. On the centre of this wheel is fixed a screw similar to that on the nose of the mandril, and to this is chucked the work to be turned. The first plate moves, of course, concentric with the spindle of the lathe; but the slide, with its circular plate, can be moved so that the work revolves with any degree of eccentricity required.

Epicycloidal turning is another beautiful variety of the art. Like eccentric turning, this is performed by a chuck peculiarly formed, and so adjusted as to be totally unintelligible without the aid of numerous figures; we are under the necessity, therefore, of referring the reader to the works quoted at the end of the article for a full explanation of it. In Bergeron's work, he will find beautiful engravings of the apparatus for this and the other varieties of ornamental turning, with minute descriptions.

Elliptic turning will be found described under that title.

The lathe for spiral turning is constructed as follows. On a shaft lying above the bed are three drums, or large wheels, with broad rims, that on the extreme left being smaller than the other two. To the circumference of the latter is attached a cord, which is stretched tight to the end of a strong elastic beam or spring fixed at the roof. On the bed, beneath this drum, is the fixed head, which consists of two puppets fixed at about two and a half feet asunder. In the top of each puppet is fixed a brass bush, in which the spindle, which is perfectly cylindrical, moves as directed by the leading screw, consisting of a cylinder of wood, firmly fixed on the spindle between the two puppets, on which is screwed out a screw of the same pitch as that required to be made. This is effected by placing beneath, and close to the cylinder, a wheel having a thin, round, or curved edge and turning on centres in a forked frame, in the manner of a framed pulley. The frame of this wheel is fixed on a stiff centre, so as to be capable of being set to any angle. If the spindle be then caused to revolve, it will also move in a longitudinal direction, in exact proportion to the divergence from a right angle, at which the wheel is set, and there will be traced on the cylinder a screw, which, when cut to fit the edge of the wheel, is a leading screw. These leading screws may be multiplied indefinitely, by shifting the wheel to different angles, to mark any number of cylinders or leading screws that may be required. On the spindle at the front of the leading screw is a wooden pulley, round which passes the cord which comes down from the large drum on the left; it then passes down and is fixed to the left corner of the treadle, the other end of which is raised by a cord passing straight from the treadle to the large drum on the other end of the shaft. By pressing down the treadle, the cord, which, as before remarked, passes round the pulley on the spindle, causes it to revolve; it also, by unwinding from the drums, causes them and their shafts to revolve, and the smaller drum, as it revolves, warps round it the cord attached to the spring in the roof, thereby bending it. It is evident that, whenever the pressure of the foot on the treadle is removed, the elasticity of the spring will cause it to pull off the cord which held it down, and cause the small drum round which the cord was wound, and the other drums, and the spindle, to revolve in the opposite direction to that caused by the descent of the treadle.

The shifting head consists of two puppets and a spindle, the same as that just described for the fixed head. Solid on the head of each spindle is a socket or hollow cylinder, in which is fixed, by means of a side-screw or otherwise, a strong taper screw; one of these screws is inserted into each end of the piece of wood to be turned. The rest has a groove, through which the wood passes, in order to prevent the longitudinal motion from displacing it. It is evident that no more length of twisted work can be produced at once than the length of the leading screw; but by shifting the rest, and taking care that the cuts join accurately, the twist or crew may be continued to any desired length. By means of this every variety of twisted work can be produced.

The reciprocating motion of the spindle may be varied by the introduction of other apparatus for its introduction than the screw we have described. By means of elliptical or other rubbers placed at the extremity of the spindle, singular compound motions are produced; and when these are combined rubbers to cause circular motion, as in the rosette lathe, an immense variety of beautiful and fanciful figures is the result.

For full information on lathes and turning, the reader may con- sult the Transactions of the various societies, and the following works: L'Art de Tourner, par Charles Plumier, Lyons, 1701; L'Art de Tourner, par Paulin Desormeaux, Paris, 1824; Manuel de Tourner, par Bergeron, Paris, 1616; Ibbetson's Specimens of Eccentric Circular Turning.