Hollow balls containing compound solids formed of cones or rays, and other shapes attached by their bases, are produced in much the same manner as the Chinese ball, but with some additional precautions. The sections figs. 569. 570, give such a figure, formed of six acute cones attached to a cube, contained within a single spherical shell.
The solid sphere while in the plain chuck is marked with six equi-distant centers, as in the last example, it is then transferred to fig. 562, and radial recesses of the form shown in section, at A. C and D, fig. 570, are turned at all the six centers. The recesses are about one eighth of the circumference of the ball in diameter, and are equal in depth to the thickness of the external spherical shell together with the width of the blade of the separating tool; a projection being left at their centers, to form the extreme points of the cones. The cones are then turned to shape, and a portion of the external shell separated from its contents, at every center, seriatim; the first being turned at B, and the second at A, with the grain of the material running in the direction of A B.
Fig. 569. Fig. 570. Fig. 571.
The horizontal groove a a, is cut into the solid ball with narrow flat, right and left side tools, to a depth determined by a gage or turning square; the inner side roughly forming the angle of the cone, all of which is left too large or unfinished. The spherical groove separating the shell, is then commenced with a small tool, the width of the stem and the blade of which, does not exceed the distance between the rough point of the cone and the edge of the radial recess; the tool being used in the guide, fig. 566. When this tool has cut to its full extent, or to the first dotted line in the direction B to D, it is exchanged for one of the inside hand tools, figs. 579 - 581, then used to widen the groove a a, and to turn away c c, the material surrounding it. These tools are similar to inside parting tools, sharpened upon the ends and upon both sides of their blades, they are used in ordinary handles, and require care to avoid damage either to the cone or spherical shell. The corner of c, being turned away to the first dotted lines, allows space to introduce a longer separating tool, to continue the circular groove so far as the second dotted line; after which, c is next turned away to the same distance with a longer inside tool, applied as in fig. 569. Sufficient space being thus obtained for the manipulation of the tools, the face of the cube is turned flat, and the cone finished to the gage of a thin metal template, fig. 571; the rest being placed rather high, that the left side tools used may be slightly inclined to the axis of the cone.
The first of a series of five conical wood stoppers, shown in section fig. 572, the exact counterpart of the radial aperture in the shell and of the cone, and abutting against the face of the cube, is then made, and placed in the work to support the internal solid figure while turning the remaining cones. The stoppers are pierced cylindrically to avoid damage to the points of the cones, and are cut with internal screws for the insertion of a handle by which they are subsequently withdrawn. Their external surfaces are turned to agree with that of the ball with a flat tool on the armrest, or they may be finished exactly with a narrow round tool, fig. 573, used in a metal guide having two projections bearing upon the surface of the sphere.
The ball is then reversed in the chuck and the foregoing repeated at A, and subsequently, at the four centers upon the line C. D. These latter require very careful and gentle turning with sharp tools, as the grain is then across the axis of the cones, while the tools also cut into the sides of the stoppers, inserted at A and B. When the last cone is completed, the five stoppers are withdrawn, in the reverse order to which they have been inserted, the last pair at A. B being both loosened before either is removed. The ball and star is frequently employed to form a portion of the stem of some other work, the parts of which are attached to opposite apertures, and are pierced with holes to receive two of the rays, to hold the points also in position. The effect of the specimen is enhanced when the solid is formed of eight or twelve points; the centers for these are set out on the sphere, as for the geometrical solids, the apertures are less in diameter, but the manipulation is otherwise the same.
The ivory balls sold in the bazaars of Singapore, fig. 574, have numerous small loose cones or points retained in cavities upon the surface; they are very similar to an ornament made by the Chinese in porcelain, and both are supposed to be derived from the formation of the lotus-nut. On rotation of the balls the points as they arrive at the under side fall outwards to their full length, while those towards and upon the upper surface, drop back into, and are nearly concealed within their cavities, the points alone standing just above the surface. The little points number from twenty-five in the smallest, to sixty or more in the larger specimens, and it is affirmed that they are cut from the solid material of the ball. This is incorrect, but the deception is excellent, the Singapore balls being turned in white ivory having little visible grain; a close inspection, however, shows that the grain of all the points coincides with their axes.
The points are difficult to extract, but if one be forced out, it, and its radial receptacle, are found to have the sections, fig. 575. The cavities are rounded and undercut, while the largest diameter of the cone, above its rounded base, tightly fits the orifice of the cavity and requires some force to make it enter. This ball has been alluded to, as being to some extent the reverse of the last described; it can be easily copied, taking care that the ivory used matches in colour and quality and has little grain, its manufacture requires no special instructions.