The milling machine is a motorized machining tool. Machining involves shaping a component by removing material using a cutting tool from the raw material.

The milling machine consists of two major elements: the milling head which carries the spindle and the table arranged perpendicular to it, on which the material to be machined is fixed.

The rotating spindle carries the milling cutter (the cutting tool). Unlike a lathe, it is the tool that rotates, while the material remains fixed. Depending on the complexity of the machine, the spindle of the milling machine can move on a number of axes ranging from 3 to 5 axes simultaneously. In all cases, the spindle can move on the three linear axes (X, Y, and Z) and, sometimes additionally, on one or two of the three rotational axes (A, B, and C), respectively perpendicular to each other.

The shape of the milling cutter can vary depending on the machining to be performed. It can be cylindrical, conical, spherical, toric, or of a much more specific shape (for gear cutting, for example).

The rotation speed of the milling cutter is determined and adjusted according to its diameter and the nature of the material to be machined. These two criteria also govern the speed of axial tool movements. Highly versatile, the milling machine can also perform drilling or tapping operations. In such cases, the milling cutter is replaced by a drill or a tap.

Simple machines, as we consider them here, do not have automation. The spindles of such milling machines are manually moved by cranks operated by the operator.

Sometimes, machines combine a lathe and a milling machine, and these are referred to as combination lathes. Like lathes, milling machines were automated in the early 20th century with mechanical cam controls first, and with computer numerical controls (CNC) from 1980 onwards. Most milling machines used in watchmaking today are integrated into versatile CNC machining centres.