Custom CNC milling machine is any type of machining service, a specific type of machining for high precision and low tolerance parts on small to medium production runs and prototype machining. The term "custom CNC" is used to describe machining operations at the request of the customer where the machine's capabilities are adjusted to meet the specifications and requirements of the customer. Most CNC machines can achieve operations of up to and even greater than 0.002mm. When the machine exceeds this tolerance the parts created are typically rejected by the machine and the manufacturer. This is due to the fact that the CNC machine was not designed and built to perform this specific operation. When the machine is equipped with software that allows it to compensate for the different types of deviations, the machine might experience from these deviations the parts are usually accepted

With advances in computer numerical control (CNC) technology, manufacturers have introduced new capabilities into the popular line of CNC machining metals such as aluminum, brass, steel, titanium, and plastics. The material is manipulated in intricate details with the use of CAD software. For example, when the brass is being cut in cross sectional pieces it is melted in a furnace under high pressure and then the pieces are cut out with CNC machinery. Plastic is also produced by a CNC machine but this process is different because instead of liquid cooling and heating of plastics, a cold process is used that creates a hard plastic material. Many of these new applications are being used for precision components in the military, aerospace, and automotive industry.

CNC milling machines are used in the vertical machining centers as well as in other types of manufacturing such as mold making, stamping, and engraving. These specialized machines are able to cut through many types of plastics with accuracy to produce accurate parts that are absolutely perfect. The accuracy of these machines has made them one of the most important parts of any industry. When used in a vertical production center, this technology is the wave of the future for every type of industry.