A machine tool is a machine capable of transforming the shape and size of objects of any material, by selective removal of super-material in various shapes, using tools. The term machine tool is usually used to define machines that use a source of motion and therefore of energy other than human motion, although sometimes they need an operator to make them work. The components of a machine tool are various, generally they consist of a frame (called a bench), one or more electric motors, the drive head (the most complex and important component), the shafts through which motion is transmitted.