A power tool is a tool that is actuated by an additional power source and mechanism other than the solely manual labor 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, such as in powder-actuated tools, or even natural power sources such as wind or moving water. Tools directly driven by animal power are not generally considered power tools.
Power tools are used in industry, in construction, in the garden, for housework tasks such as cooking, cleaning, 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 precision. A typical table saw, for instance, not only cuts faster than a regular hand saw, but the cuts are smoother, straighter, and more square than what is normally achievable with a hand-held power saw. Some stationary power tools can produce objects that cannot be made in any other way. Lathes, for example, produce truly round objects.
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 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. The global market for power tools is $33 billion (in 2016) and estimated to reach $46 billion in 2025.
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 by 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. Compressed air is universally used where there is a possibility of fuel or vapor ignition - such as automotive workshops. Professional level electric tools differ from DIY or 'consumer' tools by being double insulated and not earthed - in fact, they must not be earthed for safety reasons.
While hand-held 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 1930s, power tools 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 1930s, companies started to experiment with housings of thermoset polymer plastics. In 1956, under the influence of Hans Erich Slany, Robert Bosch GmbH was one of the first companies to introduce a power tool housing made of glass filled nylon.
Power tools include: