Curiosities
Many turners take special interest in the production of objects in the lathe, that at first sight appear impossible to be produced solely by its means. Inasmuch as such works manifest the skill and patience of the artificer, they will always meet with appreciation; and, although otherwise useless, they serve as elegant objects of vertu, and are well worthy a place among the rare ornaments of the drawing rooms. When first the Chinese balls, consisting of a set of hollow spheres one within the other, all exquisitely carved, were brought to England, it was believed they were made in hemispherical pieces, united round the equatorial line with some kind of cement, the joint being carefully concealed. I am not sure that they are made in a lathe in China; but, at all events, they are so made in England, and our home productions almost rival those of that strange yet clever nation. I say almost, because the carving in ivory done by the Chinese is in some respects unequalled, nor do I suppose that work requiring in many instances years of patient industry could be made to repay the cost of manufacture in England. No sooner were these curiosities in vogue here than all kinds of similar impossibilities were manufactured. Stars with from three to a dozen rays made their appearance, enclosed sometimes in similar sets of hollow spheres—the rays projecting beyond the limits of the outer shell—others were wondrously enclosed in cases with flat sides, cubes, pyramids, six, eight, twelve-sided hollow cases, all turned fairly in the lathe, were produced with similar contents, so that the apple in King George’s dumpling became a very secondary wonder. The starry inmates were evidently too large for the houses; yet there they were—legs and arms, of course, sticking out through doors and windows, simply because there was no room for them inside. We will penetrate the mystery, commencing with a single hollow ball containing a star of six rays, the bases of the latter standing on a central cube.
In the first place a perfect sphere is required, and consequently the slide rest and template, or spherical rest, must come into requisition unless the turner can produce a ball by hand tools alone. Let this sphere, or rather its boundary line, be drawn on paper of full size with the compasses, Fig. 262, A, B, C, D. Draw the diameters A, D, C, B, at right angles to each other. This will give you five points, which on the sphere itself (on which these lines will have to be drawn, including also another, answering to A, B, C, D) are centres of six openings, here represented by the circles, through which the tools have to be introduced to hollow out the sphere and form the star. The points of the latter will be in the centres of these openings. Draw in addition the plan of the central cube, and one ray of the proposed star; next draw an inner circle, here dotted to mark the thickness of the outer envelope. The object of this drawing is to enable you to make a set of curved tools, one of which is shown black at E, and a set are marked on a plate of steel, from which they must be cut out. A close inspection of the figure will show that if ball, Fig. 262, were turning on the point A, A D being its axis of revolution, tools of the given section introduced at D would cut away the material round the point or ray, leaving the latter standing;21 and this operation repeated at the five remaining openings would entirely free the central cube with its rays according to the proposed design. The tools have to be introduced in order, beginning with the smallest; and although the above remarks will make clear the principle, there are several points to be attended to in practice, and some few accessories are required which will now be explained. It is evident that for every different sized sphere fresh sets of tools will be requisite, which will also vary in pattern according to the intended form of the central base on which the rays stand; a cube or flat-sided solid requiring one tool at least, with a rectilineal edge; spherical or other solids demanding others whose ends are of different section. Hence, in all cases, full-sized plans of the proposed work must be drawn, and special tools designed therefrom.
Fig. 269A is introduced to show more clearly the result of the application of the first set of tools, or rather of the first application of the set, as the latter are used throughout.
The blackened part will be entirely cut away in this operation, the shaded part meeting it will be removed when the tools are transferred to the adjacent opening, the cuts meeting those first made. Hence the tools need only reach from a to b, and can be more easily introduced than if the curved part were longer. Gauges, Fig. 269B, A, must likewise be made of thin brass or tin, that the progress of the work may be examined, and each opening in the sphere should likewise be measured with a gauge, or with compasses fixed to one width by an adjusting screw.
The proper chuck for this work is the capped ball chuck already described, by loosening the cap of which any one of the six openings may be brought under the action of the tool, these openings being, in fact, bored out simultaneously with the formation of the star. After the first point or ray of the star has been completed, the ball may be reversed and the opposite ray formed. These are now to be secured by plugs, which are to be turned conical, to fit the opening of the ball at one end, and of a length to rest upon the central cube at the other, being also bored out to fit over the rays, which they should embrace closely at top and bottom, even if not at the other points of its length. (Fig. 269C, A and B.) This is to be repeated as each ray is formed, so that the central star may be held in place until the work is finished, when the plugs are removed, and the star will be entirely detached. The above-named tools being straight on the right hand side of the shank will not form a finished conical point or ray. Hence it is recommended to file away that side, so that when flat upon the rest, the back of the tool may be an exact counterpart of a ray, Fig. 270, A. There is, however, no absolute necessity for this, as the star point can be first made blunt, with perpendicular sides, which can then be neatly finished by a separate tool made for the purpose, and kept up to a very keen edge. The first and smallest of the set of tools here shown, is the one with which the flat sides of the cube are formed, and it must be bevelled from underneath, so as to present a cutting edge on the end. The curved tools should cut on the end and both sides of the crook.
It is quite possible to make the above in mahogany, but a closer grained wood is much to be preferred, as the tools used—which are held flat upon the rest—are rather scraping than cutting, and mahogany, and fibrous woods in general, cannot be thus worked neatly. Boxwood is, in every respect, the best material to begin upon, ivory and blackwood being reserved until the eye and hand have become accustomed to such work. The whole operation requires great care, and is rather tedious, but the result ought to be a sufficient reward. The external surface may, of course, be ornamented with the usual apparatus, but the star should be left clear and sharp. The edges of the openings should have a light beading, cut with a bead tool, Fig. 271, A and B.
Notes
21 There is an error in the position of this tool, which, thus placed, would not leave the point of the star. Fig. 270 will explain the method better.