CNC A simple definition. In the simplest terms, Computer Numerical Control allows for the automation of machine tools. Rather than the manual control of a cutting instrument, or even mechanical cutting to a set template, in CNC the computer is fully responsible for moving the cutting heads on a lathe, the wire on an EDM, or the bits on a mill. Drilling is performed on a drill press or a milling machine. Edge Finder Two concentric cylinders that are spring loaded together. It can be placed in a collet of a milling machine. Endmill A cutting tool used on a milling machine to cut the side of a workpiece.