PNEUMATIC TOOLS. 140 PNEUMATIC TOOLS. action being exactly analogous to that of a man driving a cliisel with a hand liainnier. The near end of the cylinder termiuutes in a handle by which the tool is held by the operator. Coin- pres!^ed air is conveyed to tlie cylinder by means of a suitable connection or a flexible hose. The variety of constructions by which the piston stroke is actuated and controlled is large, but generallv speaking all pneumatic hammers may be classed either as valveless hammers or valve hammers, one of the former class, the Keller tool, being .shown in the diagram and in various appli- cation on the accompanying plate. The valveless hammers have no valve beyond the striking pis- ton, this being itself a valve to effect the proper admission of air to alternate ends of the work- ing cylinder. In the valve hammers a recipro- cating valve, working eitlier at right angles to or parallel with the striking piston, acts in com- bination with it to regulate the inlet and the exhaust of the compressed air. There are several constructions of both valve- less and valve hammers, each of which is con- trolled by jiatents owned by the manufacturers of such tools. The general characteristics and comparative merits of the two forms of construc- tion may be suiimiarized as follows: Valveless hammers have essentially a short stroke, and al- though economical in air consumption in relation to the number of blows given, they do not com- pare with valve hanuners in giving powerful blows, which are necessary in heavy chipping and riveting. Owing, however, to their simple con- struction, they have probably a longer life than valve hammers, anil for such purposes as beading flues, light calking and chipping, and especially carving in stone, they compare very favorably with their rivals. The speed of the valveless. hammers is very high, being from 10.000 to 20,- 000 strokes per minute. The speed of valve ham- mers for ordinary work ranges from 1,.500 to 2.000 blows per minute, although they can be driven much faster. Their stroke is consider- ably longer than that of valveless hammers, and the blow struck is correspondingly greater. These characteristics of valve hammers make them most suitable for general and hea"j' clip- ping, calking, and riveting. This comparison is a fair summary of recent engineering opinion on the subject, but advocates of one or the other form naturally contest the claims of their op- ponents. The preceding description has referred particularly to hammers : by replacing the ham- mer tool struck by the piston as above described with sharpened or otherwise specially formed tools we have the hammer converted into a tool for chiseling, chipping, beading, calking, rivet- ing, etc. In operation the apparatus is held by the handle so that the tool presses firmly against the work : air pressure is then turned on by pressing a trigger or thumb lever on the handle and the reciprocating piston begins to strike the tool, which is thus caused to cut or hammer the work in front of its nose. As pre- viously stated, the blows are exceedingly rapid, their soimd coming to the ear as a continuous buzz, and they depend for their effect upon their great frequency rather than upon their individ- ual energy-. Pneumatic pereussinn tools are made in a variety of sizes, but with the exception of riveters their weight and dimensions are kept small enough to permit them to be manipu- lated by hand. As specially designed for rivet- ing work the percussive pneumatic tool re- quires brief special description. Any of the regular hammer tools may l)e used for riveting in connection with a holder-up for supporting the butt of the rivet, but such work is more effectively accomplished by heavier tools having a longer stroke. The yoke riveter is another common form and consists of a U-shaped yoke having at the end of one arm an inwardly projecting holder-up. The yoke riveter is made in .several modifications designed for special purposes and requires generally to be handled by chain or pneumatic hoists or other power. ( For illustration, see Metal- Working .Ma- ciiiNEBY. ) In clipping tools the stroke of the piston is reduced enormously in speed and it is provided with a piston rod which acts on a suit- able hinged link construction to convert its rec- tilinear motion into a pincer-like movement of the cli|)i(ing edges or jaws. In the forms of per- cussion pneumatic tools des<ribed the intensity of air pressure used is from 80 lbs. to 100 lbs. per square inch for all work except riveting, where it is usually increased up to 125 lbs. per square inch. Rotary Tool.s. Rotary pneumatic tools, com- monly called portable pneumatic drills, are used for ilrilling and boring wood and the analogous operations of reaming, tapping, tube-expanding. Piston Blade Blade Packin? Throttle Handle Throttle SIteve RockerPin .Spade Handle Cylinder Head Centre Pin RockerPin Jourr .. Journal Bushing - Thrust Bearing(al. Steel Ball-'/ Bearing Nut Throttle Handle -' Cylinder -:ston Thrust Washer Thrust Bearing (b) -Drill Chuck SELLER PSECMATIC DRILL OPERATEP BV ROTARY MOTOR. screwing nuts on bolts, boring cylinders and Cor- liss engine valve seats: also for turning crank pins, grinding steam-pipe joints, and cleaning castings. The method liy which compressed air is utilized for driving the drills is generally by means of single or double acting cylinder motors, the cylinders of which are sometimes fixed and sometimes oscillating, which actuate suitable mechanism for turning the bit and are inclosed in the body of the drill. Rotary motors are also used, and an example of one of these, the Keller tool, is shown diagrammatically in the illustra-
