A power tool is a tool that is actuated by an additional power source and mechanism other than the solely manual labour used with hand tools. The most common types of power tools use electric motors. Internal combustion engines and compressed air are also commonly used. Other power sources include steam engines, direct burning of fuels and propellants, or even natural power sources like wind or moving water. Tools directly driven by animal power are not generally considered power tools. Power tools are used in industry, in construction, and around the house for purposes of driving (fasteners), drilling, cutting, shaping, sanding, grinding, routing, polishing, painting, heating and more. Power tools are classified as either stationary or portable, where portable means hand-held. Portable power tools have obvious advantages in mobility. Stationary power tools however often have advantages in speed and accuracy, and some stationary power tools can produce objects that cannot be made in any other way. Stationary power tools for metalworking are usually called machine tools. The term machine tool is not usually applied to stationary power tools for woodworking, although such usage is occasionally heard, and in some cases, such as drill presses and bench grinders, exactly the same tool is used for both woodworking and metalworking. The term power tool is also sometimes used as a buzzword, meaning a technique for greatly simplifying a complex or difficult task. Safety: While power tools are extremely helpful, they also produce large amounts of noise and vibrations. Using power tools without hearing protection over a long period of time can put a person at risk for hearing loss. The US National Institute for Occupational Safety and Health (NIOSH) has recommended that a person should not be exposed to noise at or above 85 dB, for the sake of hearing loss prevention. Most power tools, including drills, circular saws, belt sanders, and chainsaws, operate at sound levels above the 85 dB limit, some even reaching over 100 dB. NIOSH strongly recommends wearing hearing protection while using these kinds of power tools. Prior to the 1930's, power towels were often housed in cast metal housings. The cast metal housings were heavy, contributing to repetitive use injuries, as well as conductive - often shocking the user. As Henry Ford adapted to the manufacturing needs of World War II, he requested that A. H. Peterson, a tool manufacturer, create a lighter electric drill that was more portable for his assembly line workers. At this point, the Hole-Shooter, a drill that weighed 5 lbs. Was created by A. H. Peterson. The Peterson Company eventually went bankrupt after a devastating fire and recession, but the company was auctioned off to A. F. Siebert, a former partner in the Peterson Company, in 1924 and became the Milwaukee Electric Tool Company. In the early 30's, companies started to experiment with housings of thermoset polymer plastics. In 1956, under the influence of Dr. Hans Erich Slany, Robert Bosch GmbH was one of the first companies to introduce a power tool housing made of glass filled nylon.
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