The ordinary stamp, consisting of an anvil, two guide rods, pulley, and a hammer that is worked by means of a band or rope upon the principle of the falling weight, is a very useful arrangement, and is used extensively for raising and stamping sheet metals on account of simplicity of construction and cheapness, when strength is required rather than accuracy. Different opinions are held by users as to the classes of work upon which this machine should be employed, and there seems to be good reason, judging from recent results, for stating that it is frequently better to employ a strong machine, in the form of a power stamping press, that is worked by a crank shaft. This point must, however, be settled according to the class of work to be done. There are many varieties of stamped goods, and necessarily a large number of special stamps and stamping machines, many of which are worked upon the principle of the falling weight, some of the newer types are worked by cranks and cams.

The case of producing an ordinary washing basin, say, 16 in. diameter and 5 in. deep, is an instance where a number of"force"or top dies, would be required if the basin is made in the drop stamp. These"forces"will be of different shapes, varying according to the number of stages through which the article passes before reaching the final stage. Each"force"may require two or more blows upon the work, according to the actual shape of the article, in addition to which the basin will require annealing at the various stages to prevent splitting or cracking, since in stamping processes every blow of the top die, or"force," hardens the metal, frequently causing the article to split or burst. In many cases a suitable and powerful raising press will raise the article at one blow, thereby saving l>oth time and labour. On the other hand, there are classes of work done successfully under a drop stamp that could not possibly be done economically under a stamping or raising press. From this it will be readily understood that the selection of a machine to do some particular work will frequently require the opinion of an expert.

The ordinary drop stamp, fig. 206, is generally used for hot stamping or drop forgings. The iron in the block should be dense and tough. The practice of having them cast direct from the blast furnace, though cheap, does not

Fig. 206, give good results, as the face is too soft to withstand the effect of the hammer continually falling on to the lower die. Forged steel hammers are to be preferred to steel castings. The heavier the block is over that of the hammer the more effective is the latter. A good ratio is 12 to 1, and for steel drop forgings it should be 14 or 15 to 1. Stamps in which soft metal"forcers"are used, a ratio as low as 8 to 1 may be adopted. The stamp block should have a large and well proportioned flange and a level base. The supposed economic practice of having these cast in open sand is not a good practice. A level block base can be bedded more solid upon its foundations than an uneven one.

Fig. 207.

The advantage of the type of double-stamp, fig. 207, is its usefulness for light or small drop forgings of irregular shape and thicknesses, in which the bar of iron or steel needs some preparation to mould it to suit the form of the finished die. The first, or the stamp on the left, is fitted with forging tools that serve to rough shape, that is, to elongate or thin down the bar in one part, while its adjacent part is required the full thickness. This is necessary f>r economising the raw material and reducing the superfluous metal to a minimum. In this double-stamp the first hammer is called the dolly, and the second the finisher. It is found in practice, when making steel stampings, that both hammers cannot be used for finishing, as the concussion and rebound of the one hammer tends to the up-setting and loosening of the dies under the next hammer; but this is not so important when one hammer only is used for finishing and the other used for rough-shaping the material, because the dolly tools are comparatively unimportant in their setting, and the more solid blows are made by the finishing stamp. These latter can receive careful attention to keep them truly and firmly set. When used in this manner the double-stamp economises space, heat, and time in the transfer of the work from the first to the second stamp.

The drop stamp, fig. 208, is the ordinary type raised by pulley and belt. This kind of stamp is worked either by band or foot. When the work is light, the usual method is to connect a rope or strap to reach the operator's foot; this leaves the hands free to place the work upon the lower stamp die, the blow being made by the falling of the hammer each time the operator raises his foot. In heavier work the hammer is raised by the hand, then allowed to full, and whilst the operator places the work upon the die the hammer is held by the catch, as seen on the left of fig. 208. The number of accidents that have happened by stamp operators having their fingers mutilated has led to the introduction of automatic drop hammers. The object of an automatic stamp, or drop-hammer, is to raise the hammer to the required height, then allow it to fall without the attendant pulling or releasing a rope or strap which is connected to the hammer.

Fig. 208.

Diagram 1.

The following description of such a stamp, in conjunction with diagrams 1 and 2, will enable the operations to be understood. Referring to diagrams 1 and 2, on the back of the block a projecting bracket is bolted. This serves the purpose of carrying the lifting mechanism, which consists of a crank motion, rotated by a spur wheel and pinion driven by a pulley. The frame extends upwards, and carries in suitable bearings a spindle free to rotate, upon which is secured a pulley, to which is attached one end of a band of leather, steel, metallic chain, or other more suitable material; the other or fall end of such band is connected to the hammer. Secured on the outer end of the top spindle is another pulley of about one-half the diameter of the hammer pulley, and to this pulley is connected another band, the fall end of which is connected, through the 15WP medium of a U-shaped lever, to the stud pin in the adjustable crank previously referred to. The relation between the connection of the band on the hammer pulley and the connections of the band on the crank pulley are such that as the hammer rests on the die the band on the crank pulley is coiled up, so that any motion of the crank uncoils one band and coils up the other. The hammer is thereby raised to such an extent as there is disproportion between the two pulleys-that is, the stroke of, say, a 12 in. throw crank would by these means cause the hammer to be raised a distance of 4 ft., if the ratio between the crank and hammer pulleys were 2 to 1. Any shortening of the crank throw would result in a magnified shortening of the distance the hammer would be raised, and vice versa.