AIR-TOOL. McCoy's pneumatic tool consists of an automatic hammer reciprocated in a cylinder by compressed air, or by steam, which delivers a rapid succession of blows neon tool-holder into which are inserted suitable hits or chisels for (Idling wood, metal, or stone.
IL embraces in its details valves for admitting and exhausting the air, a provision for relieving the cylinder and piston from injurious friction, and for cushioning the piston and holding the bit-socket in position, to facilitate its easy and steady application to the work. It has been applied successfully to the calking of steam-boilers, the chasing of silverware, ripousse work. stone-dressing. and sculpture. The Committee on Science and Arts of the Franklin Institute made a typal recommending the award of a medal for this invention, and from their report (Journal of the Franklin lute, July. 18t49; we extract the following tion: ''As exhibited to the committee it was working at a very high speed, from the pitch of the sound probably more than 5000 strokes pet' minute. The instrument, as complete and connected ready for action, appears in the form of a short cylinder, having a flexible tube centrally connected to one end, through which compressed air or steam is supplied at a pressure of shout 40 lbs. per sq. in.. and centrally at the other end a guide or sleeve, in which the tool-holder recip rocates : into the socket of the tool holder the rutting bits, chisels, or ham mers are inserted. Upon disengaging a latch Iiy pressing a button. the ends of the cylindrical case can be unscrewed, and inside of the shell or cover is found a working cylinder. with grooves on its oilier surface and passages leading from the flexible tube at the center of the upper cylii tiler- head to one slotted cham ber in the outside of the working cylin der, and terminating in inlet ports lead ing into the interior of the working cyl inder. Another slotted chamber in the external surface of the working cylin der leads from reduction ports through the cylinder, and terminates in a channel leading to the atmosphere through the head of the cylinder. The piston is male long and fits fluid
tight. hut with a minimum of friction in the cylinder. In the piston. but working transverse ly through it. is a piston-valve, which is worked by the pressure of air admitted through the port in the side of the cylinder and exhausted through other ports in the same manner as the piston-valves of some steam-pumps, the proper ports in the cylinder being covered and uncovered by the motion of the piston. The valve consists of a cylindrical plug having two grooves formed therein with a collar between them, and fits in a cylindrical transverse seat in the piston, and covers and uncovers, at proper intervals,, admission and exhaust ports leading to the ends of the working cylinder. The piston is not attached or connected to the tool holder, but strikes upon it as a ram or hammer: a spiral spring placed around the tool-holder, and resting with one end on a shoulder in the guide, and with the other end on a shoulder in the tool-holder, serves to retract the tool-holder: the upper end of the tool-holder has an ex panded head, fitting loosely in the head of the working cylin der, and receives the blows or strokes of the piston. As the piston rises and falls in the cylinder it closes the ports and incloses a portion of the air between it and the ends of the cyl inder, and thus forms an elastic cushion and relieves the ope rator of the shock of reversing the 'notion of the piston. The piston is snrroanded constantly by a film of air nnder pressure, and, while not leaking appreciably, seems to sustain little or no wear, notwithstanding the rapid motion. The effect of the rapid and short strokes on cutting tools upon stone, wood, and metal is to produce a smoother surface than has heretofore been practicable with chisels, and with a celerity nnapproached by other means. It has a capacity to reach into angles inac cessible to rotative tools." Fig. 1 shows sectional views of the machine, and Fig. 2 its adaptation as a repot's:6 machine.