The method of turning simple or circular solids within a spherical shell, is described in forming the box, fig. 584. The solid sphere marked with six centers, as previously, is placed in the chuck fig. 562, and radial recesses rather larger than one eighth of the circumference of the ball in diameter, and equal in depth to the thickness of the external shell and the width of the separating tool, are turned at all the six centers; as at A. C. and D. in the section, fig. 576. The ball is then adjusted in the chuck with the grain running in the direction A. B; and the spherical groove separating the external shell s commenced with a tool in the guide, fig. 566, and carried more than half way from the opening at B, towards those on the line C D. The pin, a, required for chucking the interior when turning the box, is next formed by cutting the cylindrical groove c c, with ordinary narrow flat and side tools, to the depth of the dotted line ; the bottom of the groove is left flat, and the pin, a, very slightly taper to the size and depth of a template, fig. 578. The material e e, surrounding the pin, is next turned away also to the depth of the dotted line, with the inside tools figs. 579 - 581. The smallest tool widens the groove c c, giving space to insert and use the second; the spherical groove is then continued to the apertures D. C, and the remaining material at e, turned away with larger inside tools, introduced with care, to avoid cutting into the pin or the partially completed spherical shell. The ball is then reversed in the chuck and the preceding repeated, forming a second pin at A. The four recesses upon the line C. D, are then successively place central, to complete the spherical shell, with fig. 566; the last of the four cuts separating it from the interior, as in the section fig. 577.

Solids Turned Within The Sphere Continued 400339

The contained piece for the box, is then chucked in a hollow wood arbor chuck, fig. 577, and is held alternately by the one or the other pin, as the base or the cover may be under operation. The arbor is hollowed to a corresponding taper and to a depth rather exceeding the length of the pins, that its flat annular surface may be in contact with the surfaces of the work. Its external length is sufficient to permit the shell a small lateral traverse upon its contents, in the direction A, B. The external diameter is rather less than that of the apertures in the shell, which permits the arbor to revolve, and carry round the piece for the box within the shell. The latter is prevented from revolving and is held fairly quiescent, by the shafts of the hand turning tools, introduced through the openings both on the axis and circumference in turning the box; and also, by the left forefinger placed beneath it. Other methods are sometimes employed to retain the ball or shell quiescent during the turning; one being to attach strings to opposite sides of the shell, small weights being tied to the strings, which are led away over surrounding objects. In every case the tools require to be frequently withdrawn, that any accumulation of shavings between the shell and the box may from time to time be cleared away.

The under and upper external surfaces of the box are turned flat and convex, with tools analogous to fig. 580, introduced through the apertures of B and A, or, when the spherical envelope admits of sufficient traverse in the direction A to B, with these, and with a narrow right side tool, introduced through the apertures on the line C D; after which the box is divided into two portions with a parting tool. The base and the cover are then successively chucked upon the arbor chuck, and are hollowed with fig. 580, introduced through C D; the correctness of the internal surfaces being tested with gages of the form, fig. 583, or, a finishing tool may be made of that form with non-cutting portions bearing upon the edges of the cavities. The lip and the external edges are then turned with ordinary small flat, bead, round or other tools, also introduced through the apertures upon C. D; and, when the work is in ivory, the internal surfaces are polished at this stage, with whiting and water upon a linen rag, applied through the holes by the finger. Each half of the box during the turning or the polishing of the opposite piece, being alternately held back in the shell and prevented from contact with the tool or rubber, by two narrow ribbons passed through opposite holes, and tied externally at B. fig. 582.

The fitting between the box and its cover must be sufficiently secure to hold the two halves together while turning away the two pins, and yet slack enough, to permit of their easy separation and replacement by the tips of the fingers through the apertures when the work is completed. The fitting therefore is made sufficiently slack for the latter purpose, and strips of paper or ribbon are shut in between the top and the base, to give them a temporary hold secure enough for the former. The pin upon the cover, is cut off near to the convex surface with a parting tool, through D, and the portion remaining is turned through the aperture B, to a flat plate or other form, having an edge standing above the surface, fig. 584; this and the completed external surface of the cover are then polished. The pin on the base of the box is removed last, the hollow arbor chuck is exchanged for a similar solid arbor chuck, turned at the end with a recess exactly fitting the surface and edge of the central plate last turned upon the cover. The recess in the chuck and the central plate on the cover, are fixed to each other with a little thin glue, when upon the lathe, and the box is immediately adjusted to run true; turner's cement being used instead of glue, when the ball and box are turned in wood.

Fig. 582.

Solids Turned Within The Sphere Continued 400340

Fig. 583.

Solids Turned Within The Sphere Continued 400341

Fig. 584.

Solids Turned Within The Sphere Continued 400342

The pin on the base, now standing in the direction of B, fig. 584, may be also cut off with a parting tool, but with care to avoid any sudden jerk which might detach the cover from its slender chucking. Or, it may be turned away entirely in shavings from the end, with a flat tool at B; which tool is required in either case, to finish the under surface of the base, previously to its being polished. The end of the solid arbor chuck is then cut off with a parting tool close to the cover, the thin disc of wood and the glue left upon the cover, being loosened and removed by moisture. The edges of the apertures in the external shell and their intervals, may be turned with mouldings and ornaments, and the box may also be enclosed in two or more envelopes+; in the latter case, the box is first completed, and its envelope then separated into two or more as required.