Milling machines are a machine tool used for shaping solid materials and metals. Milling machines exist in two basic forms: horizontal milling machines and vertical milling machines, which refer to the orientation of the cutting tool spindle. Unlike a drill press, in which the workpiece is held stationary and the drill is moved vertically to penetrate the material, milling also involves movement of the workpiece against the rotating cutter, the latter of which is able to cut on its flanks as well as its tip. Workpiece and cutter movement are precisely controlled to less than 0.001 inches (.025 millimeters), usually by means of precision ground slides and leadscrews or analogous technology.
Milling machines may be manually operated, mechanically automated, or digitally automated via computer numerical control (CNC).
Milling machines can perform a vast number of operations, some very complex, such as slot and keyway cutting, planing, drilling, diesinking, rebating, routing, etc. Cutting fluid is often pumped to the cutting site to cool and lubricate the cut, and to sluice away the resulting swarf.