A different application of templets is sometimes met with in filing up numerous similar parts in the same object, as the arms or crosses for the wheels of clocks and other machines. The exact pattern of one spoke is filed up as a templet, which is shaded in fig. 895, and serves for the similar configuration of every spoke; the position of the templet being given by a central pin, aided by any little contrivance which catches into the 3, 4, 5, or 6 equi-dis-tant teeth corresponding with the number of arms. Many other equally available cases of the use of templets might be cited, but we must now proceed to works of the second kind, or those of an outline partially circular.
* Templets are as much used for setting out and producing series of holes in any special arrangement, as in filing works to any particular form: the most complex example of the kind that occurs at the moment to the author, of templets being used in this manner, is in drilling the side-plates of harps intended for the arbors and link-works, used in temporarily shortening the strings. The reepective positions of the holes in these side-plates require a most exact arrangement, any departure from which, would prevent that precise shortening of the string required to produce the semitones with critical accuracy, and would also cause an unbearable jar, unless the cranks of the harp were severally in true position. or on the lines of centers, so as firmly to support the tension of the strings under all circumstances.
It frequently happens that certain forged, cast and other works have parts, known as bosses, swells, collars and knuckles, that are pierced with holes, which require their flat surfaces and also their margins to be made partially or entirely concentric with the holes. When such parts occur as bosses, they often project from a flat surface, and after the central hole is drilled, some of the pin-drills drawn on page 550, or analogous tools used in drilling machines, are employed in finishing the margins: thus figs. 482 and 484 serve for facing the extremities of the holes, 483 and 485 for the external faces of cylindrical bosses or collars, used in the guidance of arms jointed concentrically with the holes, and figured cutters 485 serve for bosses with mouldings intended for ornament.
When the circular margins are discontinuous, files and templets are more or less required: thus the extremity of a forged arm, such as fig. 896, is drilled, and in the configuration of the remaining parts, if but one or two such pieces are to be made, a boss or plug of wood is turned like a, that shall fit the hole; the shoulder of the wood is then rubbed with red chalk to mark that part of the surface which is not at right angles to the hole, and the circular edge of the boss serves for the guidance of the file in finishing the exterior margin; visually rather than obstructively, as the wooden boss would be reduced instead of the file being checked. If therefore many such objects had to be filed, two bosses or templets would be made of hardened steel, and used one at each extremity of the hole, and they would be held in position by grasping the three pieces collcetively in the vice. The same general method is very largely and more rigorously followed in making joints or hinges, of which three examples will be quoted in conclusion of this section.
The brass and steel plates fig. 897, used for the joints of carpenters' rules are filed up to templets in all respects after the manner described in reference to the snail-wheel, fig. 891, and the joint -plates are inlaid by means of the file, saw, chisel, and plane, by modes that do not require to be noticed.
The joints of drawing-compasses are made somewhat differently, and mostly as follows. The solid knuckle a, fig. 898, is first drilled and made circular by aid of a templet c, and the hollow side b is filed to correspond exactly with a; the two are then pinched together in the vice on the line d d, and the parallel notches for the steel joint-plates are made in each with the saw fig. 712, page 729, as deep as the line e e. The parts a and b arc then separated, the notches in b, are completed with the framesaw, and the bottom of the notches in a, are rendered circular with the joint-saw, fig. 713, as there explained. The middle plates, when filed a little larger than the templets c, are inserted in b, and soldered in their places; the two parts are smoothed on their various internal surfaces, and united by a temporary joint-pin, and any little irregularities in the external or circular curves, (which are left purposely a trifle too large,) arc mutually detected by their want of agreement when the joint is opened to different distances; any parts in excess are very carefully reduced with a small smooth file, principally by draw -filing, after which the screw-pin with its brass cheeks or bosses is added.
The pin-drill, fig. 475, p. 547, is commonly used for cutting out the concave parts that extend to the side of small compass-joints, such as are represented in fig. 899, and also for inlaying the heads of small countersunk screws.
Larger joints with wider knuckles, such as fig. 900, are in many instances cast from patterns closely resembling the finished works. In such cases the first process is generally to remove any little external errors with the file, and to clear the angles with a small chipping chisel; the faces of the knuckles are then smoothed and inserted within one another very tightly. The joint-hole is afterwards drilled throughout all the knuckles, and which are filed up externally, sometimes under the guidance of templets put at the ends, but principally by the reduction of those high parts which get scratched or rubbed by the opposite parts, and thereby show their excess of height.
But if such joints are required to be made more accurately, the holes are first drilled in each piece separately, and rather too close in the corners; the holes are broached with a parallel broach, so as exactly to admit a steel cylinder, fig. 901, which has a square end for the brace; this rod is intended to receive the cutters, shown on a larger scale in fig. 902, which are cylindrical pieces of steel bored to fit the rod, and cut with teeth on the outer cylindrical part and on one flat surface; a pin is inserted through both the cutter andbar,sothat the two may be united after they have been placed within the joint to be worked; sometimes the back face of the cutter has only a diametrical notch to receive the driving-pin, which pushes the cutter before it as it revokes. A recess must first he cleared for the cutter with a chisel and hummer, or by a wide-joint saw or cutter, such as fig. 713; and the hollowed parts at a a fig. 900, are then cut through their length with the cutter, that afterwards serves to flatten the faces of the knuckles in exact parallelism throughout, and at right angles to the central hole.
The two halves of the joint, having been separately hollowed and faced until the knuckles will penetrate some distance 1 one another, the external parts of the joint are next separately Bled under the guidance of hard steel rings, or templets, of the same diameter as the cutter, and placed on the cylindrical rod; after which, the two parts of the joint are put together when yet slightly too large, and the central pin is inserted, in order that the rubbing of the knuckles against the corresponding hollows may denote the parts that are still too high or full; and by cautiously removing all the parts that are abraded, the joints may be made to fit very closely and accurately, and yet to move with great smoothness.
Many joints that are at the same time wide and small, as in hinged snuff-boxes, could not bo drilled, as above described, with safety, and are therefore made quite differently, by means of small tube, called joint-wire, the mode of drawing which was explained in vol. i., page 429.
For instance, in making a snuff-box, the rims for the top and bottom are fitted and jointed together before the top and bottom plates are soldered in, and the joint is thus constructed. Supposing that five knuckles arc required for the bottom, and four for the top, the nine pieces of joint-wire are cut off, and filed square at the ends; the rims for the top and bottom having been fitted so as to form the rebate, are placed together, and carefully 1 out with a semicircular recess or groove, by means of a parallel round file, or a joint-file, exactly of the diameter of the joint-wire, which therefore leaves a hollow equal to the fourth part of the circle in each rim.
Five of the joint-pieces are then strung on a wire, inserted in the hollow of the rim for the bottom of the box, and tied therein with fine binding-wire; the intervals between these five knuckles are regulated by inserting the other four between them for the moment, while the binding-wire is being fastened; after which this first series of knuckles is soldered in with moderately hard silver solder, which is usually fused with the blow-pipe. The lid is then treated in the same manner, and the bottom part of the box now serves as the gage for regulating the distance between the knuckles in the top rim. The same plan is also used by mathematical instrument makers and others, who however more generally turn the joint-pieces in the lathe, as the draw-bench forms no part of their ordinary supply of tools; and the wide joint-pieces or knuckles in mathematical works are usually larger than could be produced in that manner.