The variety of articles produced in presses and dies is constantly increasing. The cheapness of household utensils testifies to the value of the machines by which they arc made. Sheet-metal vessels, bells, lamps, and fancy goods of all descriptions, are sold at prices so close to the value of the raw material that the casual observer is at a loss to understand how they can be made for the money. To illustrate the almost boundless capaci ty of this class of machines it may be mentioned that a press fitted with gang-dies and operated by one man will cut and draw to shape in ten hours two hundred and eighty thousand brass cartridge-cups and will turn out lamp-burner caps nearly as fast. The user of such articles has his wonder at their apparent cheapness turned to indignation when lie learns that the retail vender asks a price so much above their first cost.
while not usually classed among machine-tools or metal-working machinery, bear a prominent part in the work of the modern machine-shop. They are used on masses of metal (generally malleable iron or steel, usually worked in a hot condition) for the pur pose of increasing their density, changing their form, or improving their finish. By them pasty material is worked to close up its pores and to drive out the gases and the slag; they are employed to reduce large thick masses to comparatively thin plates, to build up several thicknesses into one block, to finish objects already roughed out by other hammers or by rolls, to bend and shape pieces to desired forms, and to weld together separate lengths and shapes. The weight of blow given by hammers varies from a few pounds to a hundred tons. The weight, or hammer proper (also called the tup, or the rain, and sometimes the monkey, when free), may be attached to a helve or to a piston-rod, or it may be raised and let go free, as in a pile driver, and it may strike either "dead" or "cushioned" blows.
blows of helve-hammers simulate those given by a sledge wielded by the human arm, the helve giving an elasticity desirable in some kinds of work. This effect may be increased by the use of springs. The helve may be raised by a cam or by any other mechanical device permitting rapid release, or, as in figure 5 (p• 33), it may be worked by a crank, from whose control it never escapes.
the drop-hammer and the drop-press there is little difference. One form (fig. 6) has the weight or hammer attached to the end of a wide board, which is raised by being gripped between two rapidly-revolving rollers, and is then released by the rollers being so far separated that they no longer act upon the board by friction. In another form the weight is raised by a rope wound up by friction rollers and then released.
form of crank-hammer 8) has between the cross-head (which is driven by a connecting-rod attached to a crank) and the weight a strong spring of leather hands, thus giving a cushioned
blow.
steam-hammers have the weight attached to the rod of a piston raised by live steam, which is allowed to exhaust freely, thus causing the piston and the hammer-head to drop by their own weight. In this type the blow may be "dead," or it may be cushioned by the exhaust being closed at a certain point, so that the steam is compressed in the lower end of the cylinder. In another type of steam-hammer the piston to which the hammer is attached not only is raised by steam, but also is driven down by the same agent, thus striking the work with a force due not only to the weight of the piston and the hammer-head, but also to the steam-pressure. The blow may be cushioned or not, at the will of the operator, who can compress the exhaust at any point in the stroke. The anvil may be carried by the same frame as the rest of the machine, or, as is best in large sizes, may have a separate foundation.
For forging metal into irregular shapes, such as cranks, marine rud ders, locomotive rocker-arms, and pedestal-frames, an extra long stroke is required. For axles, trunk-bars, engine-frames, and for stamping work in forms, there is needed an extra width at the height of the anvil. Small machines have single standards or uprights; large machines with a very heavy hammer and striking a very strong blow have double uprights, which may be divided, for convenience in working, either from the front or from the side. Figure 4 (p1. shows a 350-pound hammer with a single standard; Figure 7, a 2/-ton machine with double standard. For conve nience in finishing work it is now customary to place the ram or " tup" (terms applied to the hammer-head) and the anvil diagonally in relation to the single upright. This diagonal position permits long frames to be handled freely in either direction.
When steam is taken on the top, the machine may also be used as a squeezer or vise for holding work in hand-swaging, etc. Small hammers are generally arranged not only to take steam on both sides of the pis ton, but also to work automatically any number of strokes. Very large machines do not usually work automatically. Some machines have a supplemental valve for throttling the exhaust below the piston, but per mit free exhaust above the piston—an arrangement which enables the blow to be diminished in intensity without materially decreasing the rapidity of motion. It is an advantage to have the exhaust-nozzle, with the drip-pan, so arranged that there may be used a large exhaust-pipe detached from the valve and carried by the roof, thus giving an exhaust free from back pres sure, and enabling the water from the condensed steam to be readily car ried off from the drip-pan to any convenient place below.