As opposed to drilling, where the tool is advanced along its rotation axis, the cutter in milling is usually moved perpendicular to its axis so that cutting occurs on the circumference of the cutter. The milling cutter is a rotary cutting tool, often with multiple cutting points. Milling is a cutting process that uses a milling cutter to remove material from the surface of a work piece. Process Face milling process (cutter rotation axis is vertical - 0° inclination relative to tool axis) This led to a new class of machine tools, multitasking machines (MTMs), which are purpose-built to facilitate milling and turning within the same work envelope.

The integration of milling into turning environments, and vice versa, began with live tooling for lathes and the occasional use of mills for turning operations. Milling centers are generally classified as vertical machining centers (VMCs) or horizontal machining centers (HMCs). After the advent of computer numerical control (CNC) in the 1960s, milling machines evolved into machining centers: milling machines augmented by automatic tool changers, tool magazines or carousels, CNC capability, coolant systems, and enclosures. The original class of machine tools for milling was the milling machine (often called a mill). Milling can be done with a wide range of machine tools. It is one of the most commonly used processes for machining custom parts to precise tolerances. Milling covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. This may be done by varying directions on one or several axes, cutter head speed, and pressure. Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. A 3-axis clone of a Bridgeport-style vertical milling machine For asphalt milling machines, see Pavement milling.

How does a mills slot machine work