A CNC machine (computer numerically controlled) is, in the case of a mill, a machine that can be programmed with software. It has three main components. The first is a spindle that rotates the cutter and can perform any number of cuts. It is similar to a drill, but unlike a standard drill it can also cut sideways; the spindle moves up and down (Z axis) while the table moves along the X and Y axes.
All the movements (X, Y and Z) are driven by motors that can be controlled in very small, precise increments. By combining X, Y and Z movements at the same time, extremely complex parts can be reproduced to tight tolerances. There is also a much larger motor that drives the spindle.
All these motors can be run slower, faster or in reverse as required. Machines can be fitted with various add-ons, such as lubrication systems. Tool holders can also be controlled with a pneumatic system, which allows tools to be changed quickly without manually tightening or loosening the drawbar that holds them in the spindle. Guards can be added to increase safety.
A chip tray can also be added to collect the chips produced by cutting. Inside the machine, an electronic control system tells all the motors what to do, controlling the speed, direction and movement of the axes and spindle.