The application of computers to machine tool control was a revolutionary shift in human material culture. The details have evolved immensely with every passing decade since World War II. During the 1950s and 1960s, NC evolved into CNC, data storage and input media evolved, computer processing power and memory capacity steadily increased, and NC and CNC machine tools gradually disseminated from the level of university laboratories and huge corporations to the level of medium-sized corporations.

The first numerically controlled (NC) milling machine was a Cincinnati Hydro-Tel modified in the servomechanism laboratory at MIT and completed in 1952. This development was funded by the U.S. Air Force, which was interested in reducing the need for labor in aircraft manufacture, probably to limit the power of organized labor over U.S. military readiness. However, two things make this original motive irrelevant: (1) The technology was on the horizon anyway, and (2) the technology turned out to be highly desirable for many other reasons besides increased labor productivity by itself.

A milling machine is a machine tool used for the shaping of metal and other solid materials. Its basic form is that of a rotating cutter which rotates about the spindle axis (similar to a drill), and a table to which the workpiece is affixed. Milling is a machining operation in which a workpiece is given the desired shape by the action of a rotating cutter while the workpiece performs linear movements. In its simplest form the milling cutter is a circular disc whose rim is provided with specially shaped teeth (cutting edges). Cutters are of many different kinds and shapes.

Milling is the process of machining flat, curved, or irregular surfaces by feeding the workpiece against a rotating cutter containing a number of cutting edges. The usual Mill consists basically of a motor driven spindle, which mounts and revolves the milling cutter, and a reciprocating adjustable worktable, which mounts and feeds the workpiece.

Milling machines are of the horizontal or the vertical type. A commonly used horizontal machine is the knee type (Fig.1). It possesses a massive column which contains the gearbox and spindle-drive motor and is provided with bearings for the spindle. The spindle speed can be varied by means of the gearbox, shown schematically in Fig.2. Projecting from the front of the column is the knee, whose top surface carries the saddle. The latter in turn carries the work table, which slides in guideways. On some machines the work table can perform an automatic cycle of predetermined movements: e.g., a fast run to the cutting position, a change to slow feed motion during the actual cutting, and a quick return to the initial position on completion of the cut, after which the cycle is repeated.

When the machine is taking a cut, the saddle is clamped to the knee, and the latter is clamped to the column. The knee-type horizontal milling machine illustrated in Fig.1 is a so-called plain milling machine. The universal milling machine, same as knee type, is very similar to the plain milling machine, but has additional features, including more particularly a work table that can swivel in a horizontal plane i.e., about a vertical pivot, so that it can move at angles other than 90 degrees to the spindle axis.

A third type of horizontal milling machine is known as the manufacturing type (particularly the Lincoln type), which is characterized by having a work table that is fixed in height, the spindle being vertically adjustable, since it is mounted in a head that can be moved up or down the column of the machine. These machines are designed for heavy-duty milling. The work table slides on a bed that is supported directly on the foundation of the machine.

A vertical milling machine may be of the knee type and, apart from having a vertical spindle, is generally similar to the horizontal milling machine. The spindle is carried in a head that is vertically adjustable on the column, being provided with down feed by means of worm gearing.