A machine tool shapes metal or wood into finished components. There are a wide variety of different machine tools, each with a specific focus and method of material removal. As time goes on, these machines have gone from general purpose to highly specialized and, to an extent, back to general purpose. Time has also changed the methods of operating the machines from mechanical to electronic and then to computer control.
While there are a vast number of different types of machine tools, a couple are more common than the rest. The original reason for the invention of the machine tool was to cut screw threads into wood. This was accomplished via the lathe, a tool that rotates a work piece at very high speeds while a work head selectively removes material. Lathes are still commonly used when the final work piece has a design that is symmetrical to its rotational axis.
Grinders use highly abrasive work heads to scrape material away from a work piece. Depending on the grain of the grinding wheel, this type of machine tool can remove large amounts of material or very small amounts. The courser the wheel, the rougher the final product will be and the more heat the machine will generate. Since most grinding processes generate so much heat, these machines will often incorporate a coolant flow into the machining area.
Milling machines have a cutting tool built into them. These heads bite into the metal to cut out shapes or holes. This style of machine tool is often quite complex, as the work piece needs a large amount of movement relative to the cutting head. In addition, this type of machine often has the ability to move both the work head and work piece while the machine is in operation, further increasing its complexity.
The original machine tools were very simplistic due to the technological constraints of the era. As time when on, the tools became more complex and special-purpose. One machine would perform one operation. This typically required a machine shop to have several machines and a person whose job it was to change the bits on work heads. Modern machines can not only change their own bits inside the machine, but they often incorporate a wide selection of different tools inside a single frame, allowing one machine to do the work of many.
Early types of machine tool used a system of gears and pulleys to move and work material as it passed through the machine. The power for these machines was also mechanical. It was usually a wheel turned by an animal or water.
The use of electricity changed both the method of powering the machines and the way they operated. The machines became more compact and powerful with the inclusion of electric motors and numerical control (NC) systems. A NC machine used premade punch cards or punch tape to operate the machine’s controls. In the last half of the 20th century, those cards were replaced by built-in systems, making the machines computer numerical-controlled (CNC).