The general limitations of CNC Milling are prototype size, axis movement, and drill bit size.

The size and shape limitations will vary by the machine used. The largest machines are capable of machining pieces up to 105 feet by 21 feet (These are gantry mills, needed by such companies as Boeing mill large pieces of aluminum). The smallest machines have travels of 9 inches in the x-axis, 5.125 inches in the y-axis, and 6.5 inches in the z-axis.

The shape limitations include the inability to bore square-edged holes in the material.