In all cases the entire division of the block or ring should be determined upon, and carefully marked in pencil upon the end of the piece, before the saw is used.

When a tusk is cut up exclusively for turnery-work, the first cut is more generally made where the hollow terminates, which spot is ascertained by thrusting a small cane or a wire up the tooth, and every cut is directed as nearly as possible at right angles to the curve of the tusk, or to the outer of the circle as before described.Unless the tooth is very far from circular, it is usual to prepare the principal quantity into cylinders or rings, as large as they will respectively hold, and the diagrams, figs. 51, 52, and 53, are intended to explain the best mode of centering the pieces, or placing them in the lathe. If, as in preparing an ordinary block of wood, a circle were made at each end, and the work were chucked from the centers of the circles, as at o, tig. 51, the largest cylinder that could be obtained would be that represented by the four sides of the dotted rectangle within that figure. Very much less waste would result from placing the centers so much nearer to the convex side, as to obtain the cylinder represented in fig. 52, by allowing the waste to be equally divided between the points a, c and e.

Fig. 50.

Preparation Of Ivory Etc Part 2 10037Preparation Of Ivory Etc Part 2 10038

I is however more economical, to cut those teeth which are much curved into the shortest blocks, and the figure 53, which represents the proportions more commonly adopted, shows the small comparative degree of waste that would occur in a piece of half the length of the others, when centered in the most judicious manner.

The first process in preparing to rough-turn the block, is to fid it slenderly in the lathe between the prong chuck and the point of the popit-head, and its position is progressively altered by trifling blows upon either end, until when it revolves slowly, and the common rest or support for the tool is applied against the most prominent points a, e, and c, respectively, the vacancies or spaces opposite to each, at d, b, and f, shall be tolerably equal, so that, in fact, about a similar quantity may have to be turned away from the parts a, e, and c, for the production of the cylinder, represented by the dotted lines within the figure.

The centers having been thus found, they should be made a little deeper with a small drill; and then the one end of the block being fixed upon the prong chuck, the opposite extremity.

supported by the center, is turned for a short distance slightly-conical, ready for fixing in a plain boxwood chuck, or a brass chuck lined with wood, to complete the rough preparation, unless indeed it is entirely performed upon the prong chuck.

With the decrease in length, less attention is requisite in the centering on account of the interference of the curvature of the tooth, and the pieces may be at once rasped to the circular form, and then chucked either in a hollow chuck, or else by cement or glue, against a plain flat surface; the full particulars of which processes will be found in the fourth volume in the chapters devoted to the various methods of chucking, which should have been rendered familiar to the amateur on less costly materials, before he largely employs ivory, at any rate in the unprepared state.

When the blocks of ivory are long and much curved, a thin wedge-form plate may be sometimes sawn from the end, in preference to turning the whole into shavings; the end is turned cylindrically for a short distance, just avoiding to encroach on the lower angle of the block, and, as soon as practicable, a parting tool is used for cutting a radial notch for the admission of the saw, which may be then employed in removing a thin taper slice. The process is at any rate scarcely attended with more trouble than turning the material into shavings, and thin pieces are retained for a future purpose, such in fact as those represented beyond the dotted lines at the ends of the figures.

The hollow pieces of ivory are treated much in the same manner as those which are solid, and into which latter condition they are sometimes temporarily changed, by rasping a piece of common wood such as beech to fit into the hollow, driving it in pretty securely, but so as not to endanger splitting the ivory; the work is then centered as recently explained, the chuck and center being in this case received in the wood.

With the hollow pieces, the process of turning must be repeated, on their inner surfaces, for which purpose a side cutting tool with a long handle for a secure grasp should be used; the tool should be held very firmly so as to withstand the jerking intermittent nature of the cut, until the irregularities are reduced.

For this purpose the sliding rest is very desirable, as the tool is then held perfectly fast without effort on the part of the individual, and if the chucking be correctly done, the greatest possible economy of the material is attained; the hand tools succeed very well on the outer surface, as the rest or support upon which they are then placed is so close to every point of the exterior surface, that they may be held securely with less effort, although the sliiling-rest is nevertheless desirable there also.

When the ivory hollow is thin, and far from circular, the material would be turned entirely into shavings, in attempting to produce a circular ring; the circular dotted lines, in figs. 43 and 44, page 143 are intended to explain this. Fig. 43 might be turned into an oval ring; but it is more usual to cut such irregular hollows into small square and round pieces, as explained.

When hen thin rings or short tubes arc required, they are frequently cut one out of the other in the lathe, in preference to wasting the material in shavings; this is done with the parting tool as in fig. 54; an incision being made of uniform diameter from each end, and continued parallel with the axis, until the two cuts meet in the center: very short pieces may be thus divided from the one end only.* When the rings are large and thin, it is desirable to plug them at one or both ends, with a thin piece of dry wood, turned as a plug to fill the diameter, and prevent the ivory from becoming oval in the course of drying.