CNC milling is a cutting process in which material is removed from a block of material by a rotating tool. At first glance a CNC milling machine looks somewhat like a drill press with a cutting tool protruding down from a rotating spindle. Typically the cutting tool is moved in all three dimensions to achieve the desired part shape and the tool usually rotates about an axis that is perpendicular to the table that holds the material to be cut.

While the cutting tool turns, a computer is used to control the vertical (Z axis) and horizontal (X axis) motion of the cutter and the horizontal (X and Y axis) motion of the block of material. The cutter is guided to move through the material, removing portions of the material to create the desired part/shape.