Dem/-Sb-oks Power-Haqnmer.—Fig. 3 shows a dead-st•oke power-hanimer, made by Dienelt & Eisenhardt, of Philadelphia. The rani, or striking part of the hammer. is suspended on an elastic or flexible belt (generally of leather), attached to the ex treme points of a. semicircular steel spring. The upper part of the steel spring is con nected by a rod with a crank-pin, which, being set in motion by belting, gives the reciprocating movement necessary to raise or lower the ram, in its guides, with a- speed and force entirely regulated by the fric tion-pulley. One peculiarity of this ham mer is that, although none of the force with which the ram descends is lost, the rcbound is taken up by the spring and belt on in it is suspended, before reaching the working parts ;Wove it.. In this way the shaft-bearings. crank-pins, and set-screws are preserved from breakage. It may he readily adjusted to work exclusively on thick metals, vet for ordinary work a hammer, for ex ample, will strike good 1111(.1112de blows on it bar without imy change in 1 he ad justment. Fig. 1 shows it hammer of the same kind set in u wall-bracket. This hammer has a shorter stroke than the standard hammer ; hence it is not so powerful in its blow, although it moves very rapidly if desired.
Pneumatic Hammer.—The Ilaekney pneumatic hammer is shown in Figs. 5, 6, and 7. Hammers of this kind strike their blows through power de rived from air which has been compressed in a cyl inder by a piston. The air acts when imparting its
force precisely like a powerful compressed spring suddenly released, and, in fact, it is such a spring; hence such hammers are sometimes called air-spring hammers. Fig. 5 is the single standard hammer designed for comparatively light forging. Fig. 6 is a double standard hammer, and is suitable for heavy work. The same principles of working are, however, embodied in each, as is shown in the dia gram cut (Fig. 7). The crank-yoke is attached di rectly to the air-cylinder below, which is thus given a vertical reciprocating motion in the slides. Within this cylinder is a piston attached to the hammer-head, the air, more or less of which is con fined above and below the piston, serving to trans mit motion to it and to cushion it at the end of each stroke. The admission and confinement of air in the cylinder are controlled by valves, by which air may not only be confined above the piston but also below it, thus holding the piston between two air-springs, each of which opposes the action of the other ; and this opposition is regulated at the will of the operator, so that it may be increased till the force of the blow is reduced to nothing, or dimin ished so that the full force of the hammer is real ized: the intensity of the blow depending upon the position of the valves, Harness, Fire: see Fire Appliances.
Harpoon : see Hay Carriers and Rickers.
Harrow: see Pulverizers and Harrows.