Milling machines are used to remove materials from a workpiece via a revolving cutting tool. There are two types of milling: up-milling and down-milling. Up-milling involves cutting against the workpiece movement, resulting in varying cutting forces. Down-milling cuts in the same direction as workpiece movement, generating less heat and allowing for a better surface finish. Milling machines can cut flat, curved, or angled surfaces using multiple tooth cutters mounted on an arbor or spindle. They are suitable for machining surfaces, contours, threads, and other cross-sections.