Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/445

Rh HAMMER. This well-known tcol stands quite without rival for producing the numberless effects which are due to the remarkable force of “impact.” Of all the array of hand tools in use in the industrial arts it is undoubtedly the one that could least be dispensed with, and so it must have been from the very earliest days of handicraft. A ham- mer of some rude kind must have been as essential to the shaping of an arrow-head out of a flint, as is its modern repre- sentative to the forging of a bayonet out of a bar of steel. Hammers to be used by hand are made of an endless variety of shapes, and of weights varying from a small fraction of an ounce to 23 or 30 Tb. Of the various types now in use the differences are mainly due to the special requirements of the particular trades for which they are intended, but partly also to individual fancy. A’ few examples are given in fig, 1—a being the ordinary car- penter’s hammer with a cross pane, & a claw hammer, ¢ an engincer’s, and d a shoemaker’s hammer, which last has apparently retained its form for many generations. The same may also be said of the two others in the woodcut, which are good eximples of the roughness of the instru- ments with which results of almost incredible delicacy can be produced. Of these e is a favourite hammer used in the workshops of a London firm of goldbeaters, with which, together with others not less rude in appearance, gold is hammered oat into leaves of such exceeding thinness that 250,000 are required to make up the thickness of an inch. Extraordinarily ill-shaped as f, the file-cutter’s hammer, looks, yet with this anda simple chisel the teeth of files are cut by hand with a precision with which no machinery has as yet been able to compete, at least in England.

Hand-hammers and sledge-hammers being rigidly limited as to weight by the trifling power which one man—or at most two men—can bring to bear upon them, it long ago became obviously desirable to obtain the force of impact from some more powerful source than Inman muscles, so that the weight of hammer heads might be largely in- creased and their blows mide proportionately more effec- tive, The first step taken in this direction seems to have been the introduction of the “ Hercules,” a ponderous mass of iron attached to a vertical guide rod, which was lifted originally by a ging of men with ropes, but afterwards by steam power, and allowed to full by its own weight, This was a fairly efficient tool for forging large anchors and for similar purposes, the strength of the blow and the point at i it was delivered being easily regulated. But as the demand for wrought iron increased, the necessity for more rapid as well as more powerful hammers to aid in its manufacture increased also. The lift or helve hammer (fig. 2) and the tilt hammer (fig. 3) thns came into use, and under these forms hammers may be said to have ranked for the first time as true machine tools.

Each of these consists of a heavy head attached to a beam mounted on gudgeons, which is lifted at regular intervals by suitable cams or pins carried by a revolving shaft driven by steam or other power, their chief points of difference being the relative position of the gudgeons and the portion of the beam at which the power is applied, as shown in the diagrams.

Heavy blows are thus obtained with the one, and lighter but nuch more rapid blows with the other, both, however, invariable in their intensity, the lift being always to one fixed height.

