CNC milling is a subtractive machining process in which a rotating multi-tooth cutter removes material from a workpiece that is held stationary, or indexed, in a fixture. This is the mirror image of turning: in milling, the tool rotates and the workpiece stays fixed; in turning, the workpiece rotates and the tool stays fixed.
That distinction is what gives milling its range. Because the workpiece does not have to spin, it does not have to be round. A milling machine can approach a part from the top, the sides, and — with a fourth axis or a repositioned fixture — from additional faces, cutting flat surfaces, pockets, slots, contoured profiles, and holes wherever the drawing calls for them.
A typical CNC machining centre controls at least three linear axes (X, Y, Z) and holds interchangeable tooling, so a single setup can face a surface, cut a pocket, drill a hole pattern, and tap threads without moving the part, where the machine and tooling support it. Fewer setups mean the features machined in one operation stay dimensionally related to each other; features that require a second setup depend on how accurately the part is re-fixtured. The exact axis configuration and tooling capacity of a specific machine are confirmed against your part’s requirements at drawing review.
Typical milled features include flat and stepped faces, pockets and slots, contoured and 3D surfaces, drilled and tapped hole patterns, bosses and ribs, and mounting flanges with features on more than one face.