| A machine tool is a powered mechanical device, typically used to fabricate metal components of machines by machining, which is the selective removal of metal. The term machine tool is usually reserved for tools that used a power source other than human movement, but they can be powered by people if appropriately set up. Many historians of technology consider that the true machine tools were born when direct human involvement was removed from the shaping or stamping process of the different kinds of tools. For instance, they consider that lathe machine tools were invented around 1751 by Jacques de Vaucanson because he was the first to mount the cutting instrument on a mechanically adjustable head, taking it out of the hands of the operator. Machine tools can be powered from a variety of sources. Human and animal power are options, as is energy captured through the use of waterwheels. However, machine tools really began to develop after the development of the steam engine, leading to the Industrial Revolution. Today, most are powered by electricity. Machine tools can be operated manually, or under automatic control. Early machines used flywheels to stabilize their motion and had complex systems of gears and levers to control the machine and the piece being worked on. Soon after World War II, the NC, or numerical control, machine was developed. NC machines used a series of numbers punched on paper tape or punch cards to control their motion. In the 1960s, computers were added to give even more flexibility to the process. Such machines became known as CNC, or computer numerical control, machines. NC and CNC machines could precisely repeat sequences over and over, and could produce much more complex pieces than even the most skilled tool operators. Before long, the machines could automatically change the specific cutting and shaping tools that were being used. For example, a drill machine might contain a magazine with a variety of drill bits for producing holes of various sizes. Previously, either machine operators would usually have to manually change the bit or move the work piece to another station to perform these different operations. The next logical step was to combine several different machine tools together, all under computer control. These are known as machine centers, and have dramatically changed the way parts are made. From the simplest to the most complex, most
machine tools are capable of at least partial self-replication
since they are machines, and produce machine parts as their primary
function.
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