ROTARY TOOLS. Rotary pneumatic tools, com monly called portable pneumatic drills, are used for thrilling and boring wood and the analogous operations of reaming, tapping. tube-expanding, screwing nuts on bolts, boring eylinders and Cor liss engine valve seats: also for turning crank pins, grinding steam-pipe joints, and cleaning castings. The method by 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 hit and are inelosed 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 tion and in actual use on the aeeompanying plate. Pneumatic drills are made in a large number of sizes from light drills suitable for small holes up to machines of two or three horsepower. They work with from t0 pounds to So pounds air pressure. For performing different kinds of work, assuming the size to be ample, the only change necessary is the suhsti tution of the proper tool (drill, auger, saw-bit, reamer. etc.) in the tool-bolder. A description of the motor construction of several well-known tools will give a fair idea of this mechanism. In the Little Giant drill the motor consists of four single-acting cylinders arranged in pairs and coupled to opposite ends of a crank shaft. The crank shaft carries pinions which gear with spur wheels on the tool shaft. The entire mechanism is inclosed in a shell shaped like the section of a circular cylinder, The Whitelaw drill has two double-acting oscillating cylinders geared to a crank shaft which carries a single pinion gear ing with a spur wheel on the too] shaft. In the
Boyer piston drill the motor is in the form of a three-cylinder single-acting oscillating engine, the cylinders being carried in a rotary frame, which, since the cylinder pistons are coupled to a fixed crank, rotates and by means of suitable gears causes the tool shaft to rotate. The motor mechanism is all inclosed in a cylindrical easing. Air is piped to these rotary tools by flexible hose exactly as in the ease of percussion tools.
The use of pneumatic tools has been most highly developed in the United States. hut it is extending rapidly in European countries. Their particular field of usefulness is in performing work formerly performed by hand, because of the inability of transporting the ordinary heavy shop tools to the work. For example, in riveting the connections of metal bridges during erection in the field the work has to he done on stagings and scaffoldings high in the air. These positions are inaccessible to heavy shop riveting machines, and until the advent of the pneumatic tool such work was of necessity performed by hand; the portable pneumatic riveter can he used in almost any place where hand riveting is possible with a gain in all things in which machine work sur passes hand work.