A CNC Mill works much the way a regular mill does. A solid block of material is secured to a table. The mill then cuts away undesired material until only the object remains.

The difference between a regular mill and a CNC mill is that a computer controls each and every motion of the mill. Code can either be written or programmed from a CAD file, and this code controls the X,Y, and Z components of the mill. Additionally, the code can command the mill to switch between different milling bits, drill holes, etc. All the human has to do is bolt the block of material to the table, load the code onto the mill, and watch.

Different mills work different ways. Some mills have the drill bit move over the stationary block of material. Other mills feature a stationary drill bit, with the table securing the block moving in the X,Y, and sometimes Z planes. Finally, most mills have 3 axes (X, Y, Z), but some more expensive mills now feature 5 axes (X, Y, Z, pan, and tilt).