Also called up milling. It is a traditional milling method, the principle of which is to rotate the tool in the opposite direction of the workpiece, so as to produce upward cutting force. In this cutting process, when the tool engages, it is forced to confront the working parts, creating relatively high friction, and thus generating more heat. Milling up, on the other hand, is the opposite of milling down. As the cutter begins to subtract the smallest material, it gradually cuts the largest material because it rotates.