Milling is the process of cutting and drilling material using a rotating cylindrical tool. This tool is held in a spindle and comes in a variety of sizes and forms. With 5-axis machining, there have two extra rotary axes defined by A, which rotates around the X axis, B, which rotates around the Y axis, and C, which rotates around the Z axis. The combination of additional axes depends on the machine and comes in variations, including AB, AC, or BC.