Part 3

We now come to the most difficult operation in turning, that of cutting a screw; to perform it well and easily is a proof of the workman’s skill and proficiency in the art. There are many ways of doing it; we shall therefore give the best and least expensive. The screw tools, figures 14 and 15, plate 1, must fit exactly one into the other. Fig. 15 is an outside, Fig. 14 an inside tool. As the threads may be required to be cut coarse or fine, according to the work you are engaged upon, the small grooves in the tools are made to suit. Having turned your box quite round, and hollowed it out, cut the groove upon which the lid is to fit; place the rest at a convenient distance, turn the wheel, not too fast, and move the outside screw-tool along the rest with a regular horizontal motion, and it will cut a screw, the threads of which will fill up the space between the teeth of the tool. But care must be taken to jerk the tool off when at the end of the space intended for the screw; or if it be allowed to remain stationary, cutting the wood, the threads will be destroyed, and become useless. When this is well done, turn out the lid of the box till it nearly fits the bottom, and in the same manner press the inside screw tool against the side of the cavity, draw it out horizontally as the work moves round, and if carefully managed, it will soon be made to fit upon the outside screw. As, however, to accomplish this well, and with precision, great practice is requisite, an invention, called a traversing mandrel, is frequently used, particularly by beginners: we will endeavour to give a description of its form and use.

At the end of the mandrel A, pl. 4, is a brass cylinder, I, which fits upon the end, and is kept in its place by a nut, 2, which screws firmly into it. Below this, fixed to a brass plate that rises and lowers at pleasure by turning the screw-key, B, is attached the screw-guide; (a brass plate cut into grooves of various sizes to suit the thread you wish to cut, fig. 3;) this guide moves round on a pin. To use this machine, unscrew the nut B, pull off the brass cylinder, and in its place put on the guide, C, and screw the nut in again; turn the other guide, 3, to the groove which corresponds with it, and which is usually numbered, to avoid mistakes; turn the key B till the lower guide meets the one you have just put on the mandrel, and slips easily into it. You will now find that by only allowing the fly-wheel to move _half round_ and back again, the mandrel will run backwards and forwards, and thus have the exact motion requisite for cutting a screw. Fix your rest, and hold your tool (which must have the same sized thread as the guide then on the mandrel) quite steady upon the rest, against the revolving wood, and in a few minutes the screw will be produced. The inside screw is made in the same manner, with the inside tool, by turning the rest in front of the work. Do not press the tool too hard to the wood at first, till the threads are slightly cut, so that the teeth may enter always in the same place. About six different-sized screw guides and tools to fit will be quite sufficient for an amateur turner. There is also another way of cutting screws, by means of a traversing chuck. On the mandrel, R, pl. 4, is screwed the chuck B, to which are screwed the chucks of the lathe, R. On the outside of B is turned a screw, fitted to an inside screw worked in the block C, from which extends an arm, D, sufficiently long to allow the arm E to slide up and down it; a piece of iron should be screwed to the circular block, C, of such a length as to be capable of moving in a groove that may be cut in the collar; it is intended to prevent the block C from turning quite round. The rest, G, must not stand, as usual, parallel to the work in cutting the outside screw, but at right angles, as when an inside screw is to be cut, in order that the further arm of the rest, F, may be joined to the end of the second arm, G. It is necessary that the second arm, E, shall be capable of fastening firmly the first arm, D, to any part of the rest, G, F, as also to have a joint at each end, to admit in a horizontal plane its free action. Thus, as the lathe turns to or from us, the arms must traverse forwards or backwards, which gives a similar motion to the tool, H, that is screwed firm to the further arm, F, of the rest, and thus you can cut a screw with a single point tool. Of course any unsteadiness would spoil the screw. If you draw the centre of the rest nearer to you, and thus bring the tool nearer to the arm, E, a screw of a much larger-sized thread will be cut; for as the rest, turning in its socket, moves on a centre, the further the tool is from the centre, the greater will be the radius of the circle described, and _vice versâ_.

It may, perhaps, be feared that a piece of wood so far from the collar, K, may be apt to spring; but this is easily avoided, by not making use of the chuck, B, till the screw is to be turned. Another disadvantage would seem to arise from the impossibility of cutting screws when the puppet head is made use of. But this may also be obviated by lengthening the arm, E, to the part where the screw is to be cut, and thus we have the same screw as the traversing one. The socket, S, slides on the rest, and may be fastened to it by a screw, the upper part that turns on a pivot admits the arm, E, to slide through it, which arm is held firm with a screw.

At the commencement of the work, the rest stands at right angles with the wood on which the screw must be cut; then, by bringing it back to its original angle, and sliding forwards the tool to the last thread of the screw that was just cut, we proceed to any length required. When two or three threads are cut, the most unskillful turner will be able to continue the screw with a common screw tool.

BORING COLLAR.

Fig. D, plate 4, is a boring collar, used to support any long slender body which is required to be turned hollow. Without a support of this kind it would be impossible to keep the wood in its place; and it would either incline from the centre, thus causing the hollow to be drilled out quite crooked, or it would spring from the chuck. To obviate these two inconveniences, the two collars, figs. C and D, plate 4, are employed. In the former one, which is made of iron or brass, the holes are conical, and their centres are all precisely at the same distance from the axis of the collar. In using it, remove the right hand puppet, and provide a much lower one. Through it drill a hole, the same size as that in the centre of the boring collar. The centre of this hole must be in the same line with the centre of the mandrel. The collar, when attached to it, faces the mandrel, and is held firm by a screw. When fixed, the centre hole is opposite the axis of the mandrel; and when the largest hole is used, it clears the top of the headstock to which it is affixed. The end of the work to be bored being placed in the hole which fits it, the tool is held upon the rest against its centre, and the boring is easily and accurately performed.

The collar, D, is perhaps, a simpler apparatus for supporting long pieces of slender wood or ivory, and has this advantage, that the workman can easily make it for himself. It should be constructed of very hard, well-seasoned wood. The foot, E, must be in breadth exactly the size of the aperture in the bed of the lathe, and is kept quite steady by a bit of wood thrust through it underneath the lathe. Into this collar, fit many pieces of wood with different sized holes bored through them, (all exactly in a line with the axis of the mandrel,) so as to admit large or small pieces of work, the sides being grooved, and the supports sawn to correspond: they all slide in with great ease, and are kept quite steady by an iron pin which runs through the top. The fig. G, shows the collar, with one of the supports slipped in, the other sliding upon it; H is the collar, showing the groove, and L L are two supports that fit into it. The _middle_ of the apertures of these supports, whether large or small, must always be exactly on a line with the axis of the mandrel, therefore, after they are bored quite true on the lathe, they are sawn exactly across the hole. This is a very useful addition to the lathe, not only as a support when boring holes, but also to be used with the right hand puppet, to give strength to any long slender piece of work, as a screen-handle or a pen-holder; for, being of great length, the stress necessary to the proper management of the tools would be apt to break the wood or ivory, and it is easy to make one of the ornamental mouldings of a proper size, to enable it to run smoothly in one of the supports; if too tight, the wheel will not turn, and if too loose, the work will jerk up and down.

For boring, there are many shaped tools of various sizes; 16, 17, pl. 1, are drawings of the most useful. They have no handles, but at the smaller end a hole is drilled, to admit the point, J, of the puppet, G, pl. 1. Having, with one of the turning tools, made an aperture in the work sufficiently large to allow the boring tool to enter, screw the puppet, G, firmly to the bed of the lathe, then turn the small wheel, K, till the point enters the hole in the tool, which must be steadied by holding it straight and firm with a pair of pincers. Make the wheel turn rather quickly, and with the left hand keep moving the left wheel, K, very gently, so as to force the tool into the wood. After a few turns, stop the lathe, and take out the boring tool, to get rid of the shavings and dust; move the puppet nearer and begin again. A little difficulty will be found in making the tool enter the wood, or _bite_, as it is called, but, by humoring it gently, it will soon take hold; care must be taken to keep it quite straight, and not to go too fast, or it will be liable to break. This method of boring is only used for small hollow tubes, needle-cases, crochet-needles, handles, and small work.

OF WOODS.

There are many beautiful English woods which are excellent for turning; beech is very universally used, and it should be cut into moderate sized pieces and boiled, to render it more durable, and to make it work smoothly.

Elm and chestnut are also much admired; if the latter be dipped in alum water, then brushed over with a hot decoction of logwood, afterwards with one of Brazil wood, it will be made to imitate mahogany. Green wood should never be used, as it is apt to split; it should be kept for at least a year before attempting to turn it. Some persons, if they fear the wood has not been sufficiently seasoned, cut it up and put it in a vessel filled with a ley made of wood ashes. In this it must be boiled for an hour, and allowed to remain in the liquor till quite cold, afterwards it must be dried in the shade.

Old walnut wood is very beautiful; to improve its colour, it may be put in the oven, and when worked, polish it with its own oil, very hot.

Sycamore, when grown in favourable situations, is as white and nearly as hard as holly; the cherry, yew, laburnum, and pear-tree woods, are also very beautiful; but though invaluable for plain turning, they are not hard enough, or of a sufficiently close and fine grain, to admit of ornamenting them in delicate and minute patterns. The milling tools are generally employed for them. Of all English woods, the holly is the whitest, and is rendered still more so by boiling; it is, when very good, used for inlaying, in imitation of ivory. Box is the hardest and toughest of our woods; when cut plank-wise, it is apt to warp, if not well seasoned; but its yellow colour, if highly polished, is much admired, and it will receive the most delicate patterns; it is also used as a substitute for ivory.

The foreign woods are those most prized by the ornamental turner, on account of their hardness, and the beautiful polish which can be given to them. Cocoas, or the wood of the palm, is much used for all kinds of ornamental work. It is of a beautiful brown, streaked with darker veins, and is found in the West Indies.

Ring wood is extremely hard, of a chocolate brown, with black veins; it is a good wood for turning, and comes from Brazil.

Partridge and leopard woods, tulip and snake woods, are also frequently used; the latter is of a very deep red, and very hard.

Calamander wood, a tree growing in the island of Ceylon, is very hard and heavy, and the veins in it most beautifully shaded. The principal colours are a fine chocolate, sometimes deepening almost into black, then gradually shading into a cream colour. It is a very hard wood, and takes a high polish.

African thorn is of a beautiful dark colour, and much prized when it can be obtained good, which is rarely the case.

Ebony, an exceedingly hard, smooth, foreign wood, is much admired by turners. The best is a jet black, free from any veins, and receiving a very high polish. There is some difficulty in keeping woods to prevent them from warping or cracking. The foreign woods, particularly, being usually very dry, often open in fissures while working. The best method of preserving them is to place them in a cool and rather damp place, and to rub a little oil now and then over the outsides, to keep them moist. If the wood is sufficiently large to allow of its being quartered, the danger of its splitting is much less; but the foreign woods are rarely large, as the trees are generally very high, but small in circumference. If foreign woods cannot easily be obtained, box wood and holly may be stained so as greatly to resemble them. The dying woods to be used must be in small chips or raspings. When the wood is ordered to be brushed over several times with the fluid, it should be dried between each time. If the stain is wished to be very deep, the wood should be boiled in the stain.

TO STAIN WOOD RED.

Mix two ounces of Brazil wood, and two of potash, in a quart of water; let them remain in a warm place for some days, stirring them occasionally. With this boiling liquid, brush over the wood till it becomes of the requisite colour; then dissolve two ounces of alum in a quart of water, and, while the wood is wet, brush it over with it. For a pink or a rose red, use double the quantity of potash.

A YELLOW STAIN.

Steep one ounce of turmeric in a pint of spirits of wine; let it stand for several days. Brush the wood over with it. A red yellow is made by adding to the above a little gum tragacanth.

A BLACK STAIN.

Brush the wood with a hot decoction of logwood, then with common ink.

A PURPLE STAIN.

Boil one ounce of logwood and two drachms of Brazil wood in a quart of water, over a moderate fire. When one-half is evaporated, strain it, and brush the wood over with it. When dry, brush it over with a solution composed of a dram of pearl-ash in a pint of water.

A MAHOGANY STAIN.

For a light stain, mix two ounces of madder and one of fustic in a quart of water, and boil them all together; a darker stain is made by using half an ounce of logwood in the place of the madder, and then brushing the wood with a weak solution of potash.

All hard woods are easily polished; first, they are made perfectly smooth and even, with the turning tools, after which rub them with sand paper, then with Dutch rushes, which, to prevent their breaking into small pieces, should be steeped in water. While using these, make the lathe turn quickly round, sometimes one way, sometimes the other, to prevent any unevenness, and keep moving the sand paper, &c. &c., or the edges are apt to cut lines. When this is done, and the work looks smooth, rub over it a drop or two of olive oil, wipe it clean with its own shavings, take it off the lathe, and brush it with a very hard brush, the same as those used for blacking leather.

As it is impossible to turn well unless your tools are in good order, great care must be taken to keep them very sharp. If a bit of the steel splits away, as is frequently the case in turning hard woods, grind it down till it becomes even again, then rub it on the Turkey stone, with a little olive oil, till the edge is so sharp that you cannot see it; for the gouges and hollow tools, thick Turkey stones, rounded at the edges, are sold, which enter into the groove, and the outer edges are rubbed on the flat stone.

As soon as the turner becomes quite master of his tools, he will find ivory much pleasanter to work than wood; it is not so liable to split, it turns smoother, polishes with less trouble, and shows any ornamental work much better than wood. But then it is very expensive, and very difficult to obtain good and white. New ivory may be bleached by exposing it in the sunshine, and wetting it constantly, or it will crack; but till the ivory is cut up, you cannot tell whether it will be good or not. Pieces may be bought cheaper that have a hollow in the middle, they serve very well for pedestals of vases, by screwing another bit into the hole, or for boxes, by gluing in a piece of ebony to fit the hollow. Ivory is polished _before_ ornamenting, with putty powder, ground very fine, rubbed on with a piece of linen dipped in water, dry it, and rub very hard with a bit of felt, and the polish will be beautiful. But after it is ornamented, polish only with a brush dipped in water and chalk, or even in plain water.

For dying ivory, it is first necessary to cleanse it from the grease which it always contains, more or less, and which would prevent its receiving the stain or dye. For this purpose, mix half a pound of nitre in an equal quantity of water, tie a string round the pieces of ivory, and dip them in while the liquor is hot, then plunge them into cold water.

TO DIE IVORY RED.

Take half a pound of pieces of scarlet cloth, put them into a clean earthen pot; add one ounce of soft soap, after which pour in three quarts of soft water. Boil all together for half an hour, stirring it frequently, and squeeze the cloth several times, to extract the colour. When this is done, have ready an earthen vessel, put into it as much pulverized alum as will lie upon a sixpence, pour the scarlet liquid over it, and extract all the colour from the cloth by pressing it in a canvas bag. Steep the ivory in this liquor till it becomes of the proper scarlet.

BLACK DYE.

Boil a quarter of a pound of logwood shavings in a quart of water, in an earthen vessel, for half an hour. Steep the ivory in it.

On taking the ivory out of these boiling liquors, immerse it instantly in cold water, to prevent its cracking.

ELLIPTIC TURNING.

This machine is frequently called, by those who do not understand the ellipse, an oval chuck; but it is not oval, for an oval expresses an object that is smaller at one end than at the other. Fig. 1, plate 3, is a front view of the machine. I K is the iron plate to which all the parts (except the ring, hereafter described) are fastened. A screw, similar to that on the nose of the mandrel, is riveted to this plate, fig. W, and upon it whatever you wish to turn is fixed. Fig. 2 exhibits a back view of this machine; at each of the four corners there is a short square pillar, marked D. Within these are two narrow ribs of steel, reaching the whole length of the plate I K. Each of them, being bevelled, forms an angular groove, reaching all its length. By means of these grooves the slider, F, moves up and down.

When the slider is in its place, two pieces of steel, M M, bear upon the side pieces, to which, and to the plate, I K, they are firmly attached by four screws, X X X X. The plate, F, being cast in the same piece as the slide, cannot be thrown out of its place, but moves in a longitudinal direction only, the nut, L, acting as a stop to prevent its going too far. The space between the end pieces, M M, is just equal to the diameter of the ring, O, Fig. 3, upon the outside of which they revolve when the nut is screwed upon the mandrel. Two arms, R R, are connected with it, and in each there is a groove extending nearly their whole length. This machine is connected with the lathe, and its motion obtained as follows:—E E, fig. 4, represents a headstock, through which two holes are drilled, the centres of which are precisely in a line with the centre of the mandrel, M; the ring is fastened to the headstock by two screws, I I, the shanks of which pass through the grooves and through the holes in the headstock. When the ring is in this position, it will be perceived that it can only move from side to side, and its centre must always be in the same horizontal line with that of the mandrel. Now screw upon the mandrel the nut, L, fig. 2. The plate, I K, if set exactly opposite the mandrel, will revolve in a circle; but if the centre of the ring be the least in the world on one side of the mandrel, it will revolve in an ellipse. When, therefore, the work is fastened to the screw, W, it is quite as easy to turn an ellipse as on the ordinary lathe to turn a cylinder.

Of course, the slider must move with great steadiness and freedom, to effect which, very great accuracy in the workmanship must be observed. Figs. 5 and 6 are two different views of the machine,—5 is the side, 6 the end view.

To turn a hollow sphere, the convex surface is first turned, and perfectly smoothed and finished; it must then be bored with a centrebit, to make an aperture sufficiently large to admit the tool, fig. 7, plate 1, with which the interior must be worked away. As, however, it would require a large aperture to enable you to hollow out the whole sphere, it is preferable to make six openings with the centrebit, each in a line with the centre; they must also be made at equal distances from each other, and every hole must be at right angles with all the rest, except one, which is exactly opposite to it. Place the sphere in a chuck, with the middle of any two of the holes in a line with the axis of the mandrel; turn out as much as you can of the first hole, then bring the other holes forward and do likewise; at last the excavations will be cut through.

To turn the Chinese balls, which are so much admired for their beauty and curious workmanship, we are told to proceed as follows:—As they are composed of spheres one within the other, the holes must be just deep enough to leave the thickness between each little more than the diameter of the smallest sphere. The work must be begun by forming the innermost sphere, and afterwards it must be continued regularly on to the larger, till at last the outer sphere is completed.

An immense, almost an endless, variety of figures may be worked in the lathe by carefully regulating the tools. Beautiful flowers in ivory, equal to the Chinese carving, are formed by the experienced turner, with small wheels and other instruments: medallions, even, are executed in the lathe, with machinery so constructed that the tool follows on the wood the exact lines of the head that is being copied.

Gold and silver ornaments, such as watches, snuff-boxes, and other trinkets, are worked with what is called a rose engine; plates with patterns indented upon them are fastened upon the mandrel: the screw regulates the tool, which produces an exact counterpart of the pattern.