Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/510

Rh 488 MINT inch, while in the later stages the reduction in thickness at each passage through the rolls is less than T ^ 7 th of an inch, and finally one or two &quot;spring pinches &quot; are given to the bars by simply pass ing them through the rolls without altering the adjustment. The testing of the fillets, to ascertain whether they are of the accurate thickness, is effected by the aid of the gauge plate (fig. 4), which consists of two steel bars set at a low angle in relation to each other and graduated to ,-^th of an inch. r - 4. Gauge Plate. It will be evident that the weight of the finished coin depends upon the thickness of the fillets ; and to show how accurately the rolling must be performed it may be pointed out that, in the case of the half-sovereign, a variation of sTroiroth of an inch above or below the accurate thickness (or a range of TTroTffth of an inch) throws the coin out of &quot; remedy.&quot; The repeated passage through the rolls is attended by a consider able increase of hardness in the metal, and it is therefore in some cases necessary to anneal the fillets repeatedly during the rolling. In the case of fillets for sovereigns the annealing may be entirely dispensed with if the initial thickness of the bars does not exceed f ths of an inch. Fillets for half-sovereigns have only to be annealed onco. In some European mints the fillets are annealed frequently ; in one mint the operation is performed after each passage through the rolls. The furnace used for the purpose is generally so arranged as to permit the flame to play over the fillets, which are sometimes freely exposed to its action, but are more often enclosed in cases or tubes. Muffle furnaces are frequently used. The furnace used in the Royal Mint is a simple form of reverberatory furnace. The final rolling is given by a pair of finishing rolls capable of more accurate adjustment than the &quot;breaking-down&quot; rolls. The fillets of gold or silver are in some cases, though not always, Drag submitted to an appliance known as the drag bench, shown in bench, figs. 5, 6, 7. Its object is to equalize the thickness of the fillets by drawing them between steel cylinders. The ends of the fillets are FIGS. 5, 6, 1. Drag Bench. first flattened in a little appliance, which need not be described. The essential feature of the machine now iised in the mint consists of two small steel cylinders A, A, which do not revolve, and are held in position in the plates D, D by clamp pieces F, F screwed against them. The portions of metal may be adjusted by the aid of a wheel and screw H (figs. 6, 7), and by small ad justing screws /, /. The part of the machine con taining the steel cylinders is fixed at the end of a long bench, and gearing at tho other end of this bench drives an endless chain BB (fig. 6), one link or other of F__ which catches the carriage, &quot; shown in plan in fig. 5, and drags it along as soon as its end / is depressed by the handle r. The carriage runs on the wheels d, d. The drawing of the fillet C is conducted as follows. Its flattened end is intro duced between the steel cylinders, and is grasped I ^^ by the jaws a. The jaws turn on the pin c, and while tho fillet is being dragged through the cylinders the axle of the wheels d, d tends to increase the grip of the Fl - 8. Cutting Machine, jaws by acting on their inclined ends. Directly the strain on the fillet is released, the pins i, i and the weight h loosen the jaws and at the same time raise the end of the carriage so as to arrest its further progress along the bench. The carriage is then moved forward by the handle s until the jaws enter the hollowed portion N and grasp another fillet. Formerly when fillets were rolled from thick bars this appliance played a more important part in coining operations than at present. It is now only used for fillets from which sovereigns and half- sovereigns are to be produced. Before fillets are passed on to the next operation that of cutting from them the disks or blanks destined to form the coin they are carefully tested by a skilful workman called the &quot;tryer,&quot; who cuts one or two blanks from the sides of Trying. each fillet by the aid of a cutter worked by hand. These blanks are weighed on a delicate balance against a standard weight, and the experience of the operator enables him to determine whether the variation from the exact weight will justify his sending the fillets for ward to the cutting room. In any case ha divides the fillets into two or more classes for a reason that will be explained presently. The cutters employed in the mint until quite recently were of Cutting complicated construction, but these have been replaced by a simple blanks. machine (fig. 8) which, by the revolution of an excentric A, causes two short steel cylinders, mounted on a block of iron B suitably guided, to enter two holes firmly fixed in a plate on the bed of the machine. &quot;When the fillet FF is ^- interposed between the short cylin- &amp;gt; ders and the holes, the former force _ disks of metal through the holes, ~ ~ the fillet being advanced at each *% stroke of the machine by small gripping rolls C, C, C&quot; actuated by a ratchet-wheel E, driven from the shaft which bears the excentric A. The disks pass down the tube G to a receptacle placed on the floor. In the case of very large silver coins, only one disk is cut in the width of the fillet, and in some few mints disks for gold coin are also cut in this way, but it is far more usual to cut two disks in the width of the fillet, the position of the cutters being so arranged as to remove blanks in the manner shown in fig. 9. In cutting disks for bronze coin extreme precision is not necessary, and it has therefore been found possible to obtain five at each stroke of the machine. r--- OOOOCO ~ ~