In some cases the quill is made 3 or 4 inches long, and mounted, more like an ordinary lathe mandrel, in a conical steel collar at the front, and a back center also of steel. In this case the conical hole for the tools extends about 2 inches up the quill, and a central mortise is made at the bottom of the hole, for the insertion of a lever or wedge, by which the tools are forced out, or otherwise a collar is cast upon the front end of the tools, and they are released with a forked lever.
The tools are made of iron wire, prepared from the softest stub iron, and carefully annealed, to render them as soft as possible. The conical plug that fits into the quill of the engine, is formed by casting around the stem of the tool a corresponding cone of some easily fused metal, as tin, pewter, or lead hardened with a little antimony. The moulds for casting the conical plugs are made in various forms, but the general construction will be sufficiently obvious from an inspection of the section shown in fig. 1198, in which a represents the body of the mould in which the plug is cast; b, the metal socket in which the tool and mould are fixed to retain them both central; and c, the wooden block for the support of the whole. The part a is made a little longer than the quill, and is fitted in the middle of its length with a stem and wooden handle, which give it somewhat the appearance of a hammer. Throughout its length extends a central conical hole, the angle of which is exactly a copy of that in the quill, (both holes being generally formed with the same tools,) and at the larger end of the hole is filed an angular groove to form a feather to fit in the corresponding groove in the quill. The end of the mould a, having the groove, has a short cylindrical neck turned on the outside, and concentric with the hole, and this neck is fitted into a corresponding recess in the upper part of the socket b. The socket is made in halves, fitted together with steady pins, and has a central hole for the reception of the tools. The exterior of the socket is made rather conical and fits into a corresponding hole in the wooden block c.
In preparing the tools after the wire has been annealed, they are first roughly filed into form, the small disks are filed out of the solid, the stem that projects from the end of the quill is made round, rather conical, and a little smaller at the largest part, than the hole in the socket. The shank that is to have the conical plug cast upon it is made square, slightly taper, and with a few notches roughly filed in the angles, in order that it may be firmly held in the casting. The socket b is then separated, and the stem of the tool is made to fit the central hole, rather tightly, by winding a slip of paper around it. The socket is then closed, inserted in the wooden block, and pressed tightly down, when the conical form of the exterior of the socket and of the hole, ensure a firm grasp upon the stem of the tool.
The mould a is then fitted into the recess in the socket b, which ensures the square stem of the tool being central with the conical hole, and the fluid metal is poured in from a small ladle. When the metal is set, the socket is removed from the block and separated, any superfluous metal that may have lodged on the upper end of the mould is filed off, the tool is then pushed out of the mould, and is ready to be inserted in the quill.
It is of primary importance that the tools should run perfectly true in the engine, and therefore after the plugs have been cast, the tools are fixed in the quill, and turned to the required forms, with small gravers applied in the usual manner. The rest for turning the tools is shown in fig. 1197, and much resembles that employed in the turnbench of the watchmaker; when in use the horizontal bar is passed through the mortise in the brass standard, and retained in its position by a binding screw.
The forms and sizes of the tools employed in seal engraving are very numerous, to adapt them to the various parts of the different devices, but the general shape is that of little disks more or less rounded on the edges, which is the part almost exclusively used. Some of the tools for cutting fine lines are made almost as thin on the edge as a knife, others rather thicker and more rounded on the edge, are employed for thicker lines.
For sinking large shields, and similar purposes, the tools are considerably rounded, being in some cases made almost spherical, as a tool with a rounded edge is found to cut more rapidly than one with a more nearly flat edge; and, therefore, a rounded tool is generally used for removing the principal bulk of the material in large works, and a tool with a flatter edge is used for smoothing the surface. For flat surfaces, the tools are of course made with flat edges, and to enable them to be applied to deep works without the stem interfering with their action, the diameter of the front of the tool is generally made somewhat smaller than the back, so as to make the edge rather conical, as seen in fig. 1202.
Figs. 1199 to 1205, represent some of the most usual shapes of tools, but the sizes are greatly magnified for distinctness, the tools shown in figs. 1199 to 1202, being seldom larger than one-sixth of an inch in diameter, and tools of nearly all the shapes are made very much smaller than that size, some of them being made so small as not to exceed the 1/150 th of an inch in diameter, and can hardly be distinguished by the naked eye from the stem of the tool, which appears to terminate almost in a needle point, although on examination with a powerful magnifier the disks are distinctly developed. The general form of the point of these minute tools is shown in fig. 1207, which represents the disk and part of the stem magnified about fifteen times.
These exceedingly minute tools do not admit of being formed of so small a size by the turning tool alone, they are therefore reduced as small as possible with a fine file, and are afterwards employed for works of a little larger size, until they become sufficiently small to be used for making very minute dots, such as sometimes occur in the markings of the eyes, in figures of men or animals, the full lengths of which do not exceed one quarter of an inch.