A power tool is a tool powered by an electric motor, an internal combustion engine, a steam engine, compressed air, direct burning of fuels and propellants, or even natural power sources like wind or moving water. Power tools are classified as either stationary or portable, where portable means handheld. They are used in industry, in construction, and around the house for driving, drilling, cutting, shaping, sanding, grinding, polishing, painting, and heating. 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.
Stationary power tools are prized not only for their speed, but for their accuracy. A table saw not only cuts faster than a hand saw, but the cuts are smoother, straighter and more square than even the most skilled man can do with a hand saw. Lathes produce truly round objects that cannot be made in any other way.
Common power tools include the drill, various types of saws, the router, the electric sander, and the lathe.
The term power tool is also used in a more general sense, meaning a technique for greatly simplifying a complex or difficult task.
The lathe is the oldest power tool, being known to the ancient Egyptians (albeit in a hand-powered form). Early industrial revolution-era factories had batteries of power tools driven by belts from overhead shafts. The prime power source was a water wheel or (later) a steam engine. The introduction of the electric motor (and electric distribution networks) in the 1880s made possible the self-powered stationary and portable tools we know today.
Currently an electric motor is the most popular choice to power stationary tools, though in the past they were powered by windmills, water wheels and steam. Some museums and hobbyists still maintain and operate stationary tools powered these older power sources. Portable electric tools may be either corded or battery-powered. Compressed air is the customary power source for nailers and paint sprayers. A few tools (called powder-actuated tools) are powered by explosive cartridges. Tools that run on gasoline or gasoline-oil mixes are made for outdoor use; typical examples include most chainsaws and string trimmers. Other tools like blowtorches will burn their fuel externally to generate heat.
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