pneumatic tool, instrument activated by air pressure. Pneumatic tools are designed around three basic devices: the air cylinder, the vane motor, and the sprayer. The air cylinder contains a piston that is pushed the length of the cylinder by compressed air and returned by air or by a spring. In a common type of pneumatic hammer, called a hammer drill, the piston is not connected to anything but runs freely in the cylinder. At one end of the power stroke the piston hits the top of the drill; an additional mechanism in the hammer drill turns the bit slightly after each blow. Light hand-held pneumatic hammers are used for chipping paint from metal, carving rock, and riveting. Much larger hammers are used in mining and quarrying; some of them are mounted on mechanically propelled vehicles. Hammers designed to clamp onto the side of a vat or other container are used to pack sand or concrete, the vibration causing the contents to settle. The vane motor is better adapted to rotary motion, and it can run at high speeds. In this motor, sliding vanes radiate from the end of a shaft extending into a cylinder. The center of the shaft is not at the center of the cylinder; consequently the pockets formed by the vanes and the cylinder wall are unequal in size. Air admitted through an opening in the cylinder wall at a point where the pockets are small tends to push the vanes around to the point where the pockets are large. There the air escapes through a second opening in the cylinder wall. The shaft is connected without gearing to wire brushes, drills, screwdrivers, and grinders, where high speeds are required; speeds of 10,000 to 20,000 rpm are common. With gearing, lower speeds and greater torque, or twisting force, are achieved for screw-thread tappers and for other heavy-duty applications. With suitable gearing the vane motor can drive a type of hoist to wind a cable or chain around a drum. The pneumatic sprayer applies not only paint but many other materials, such as cement and plaster in construction work. Insecticides, molten metal, and plastic fibers are also sprayed. Paint sprayers, also called air brushes, do faster work, spread a more even coat, and penetrate cracks better than do brushes wielded by hand. In a pneumatic sprayer, paint is drawn from its container by the reduced pressure created by a stream of air passing through a pipe connected with the container. The stream then entrains the paint and sprays it.

machine tool, power-operated tool used for finishing or shaping metal parts, especially parts of other machines. An establishment that is equipped with such tools and specializes in such work is known as a machine shop. Machine tools operate by removing material from the workpiece, much as a sculptor works. Basic machining operations are: (1) turning, the shaping of a piece having a cylindrical or conical external contour; (2) facing, the shaping of a flat circular surface; (3) milling, the shaping of a flat or contoured surface; (4) drilling, the formation of a cylindrical hole in a workpiece; (5) boring, the finishing of an existing cylindrical hole, as one formed by drilling; (6) broaching, the production of a desired contour in a surface; (7) threading, the cutting of an external screw thread; and (8) tapping, the cutting of an internal screw thread. In addition there are operations such as sawing, grinding, gear cutting, polishing, buffing, and honing. The tools themselves vary in size from hand-held devices that can be used for drilling and grinding to large stationary tools that perform a number of operations. Many machine tools have a name that indicates their principal function, e.g., drill press, broach machine, milling machine, and jig borer. The lathe can perform turning, facing, threading, drilling, and other operations. In order to withstand the great heat that this work generates, the materials used in machine tools must be extremely hard and durable. Thus, their working surfaces are made of such substances as high-speed steels, sintered carbides, and diamonds. To help dissipate the heat, the area of contact between the working surface and the workpiece is usually lubricated with a fluid that may also improve the finish of the workpiece's surface. Modern machine tools are often numerically or computer controlled; where a human operator can be distracted, and is limited by the speed of human reflexes, a numerically controlled machine is more reliable and accurate. See boring mill.

Industrial art of manufacturing stamping dies, plastics molds, and jigs and fixtures to be used in the mass production of solid objects. The making of dies for punch presses constitutes most of the work done in tool and die shops, and most such pressworking dies are used in the manufacture of sheet-metal parts such as the panels of an automobile body. Seealso machine tool.

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Device for making material changes on other objects, as by cutting, shearing, striking, rubbing, grinding, squeezing, measuring, or other process. A hand tool is a small manual instrument traditionally operated by the muscular strength of the user; a machine tool is a power-driven mechanism used to cut, shape, or form materials such as wood and metal. Tools are the main means by which human beings control and manipulate their physical environment.

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Stationary, power-driven machine used to cut, shape, or form materials such as metal and wood. Machine tools date from the invention of the steam engine in the 18th century; most common machine tools were designed by the middle of the 19th century. Today dozens of different machine tools are used in the workshops of home and industry. They are frequently classified into seven types: turning machines such as lathes; shapers and planers; power drills or drill presses; milling machines; grinding machines; power saws; and presses (e.g., punch presses).

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Stone Age devices, usually flint (see chert and flint), shaped by flaking off small particles or by breaking off a large flake to use as a tool. Prehistoric humans preferred flint and similar siliceous stones because of the ease with which they could be chipped and for their sharp cutting edges. They also used sandstones, quartzites, quartz, obsidian, and volcanic rocks. Stone tools were chipped by striking a block of flint with a hammer of stone, wood, or bone or by striking the block itself on the edge of a fixed stone. Pressure flaking consists of applying pressure by means of a pointed stick or bone near the edge of a flake or blade, to detach small flakes, and was used mostly to put the finishing touches on tools. Seealso stone-tool industry.

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