Milling is one of the most commonly used forms of machining. Milling uses rotary cutters to remove unwanted material. The material is cut away from the work piece in the form of small chips to create the desired shapes. It is typically used to produce parts that are not axially symmetrical and have many features such as holes, pockets, slots and three dimensional surface contours. It is also can utilize a secondary process to add or refine features on parts that were manufactured using a different process.