A keyseating milling machine, also known as a keyway milling machine, is a specialized type of milling machine that is used to cut keyways, or slots, in shafts and other cylindrical workpieces. It typically consists of a milling cutter that is mounted on a sliding carriage and is guided by a pair of tracks that run parallel to the axis of the workpiece. The machine uses a rotary cutting tool to mill slots or keyways in the workpiece.

Keyseating machines work by feeding the cutting tool along the tracks and into the workpiece, using a combination of rotary and linear motion. The cutting tool is typically a square- or rectangular-shaped cutter that is designed to cut the keyway to a precise width and depth. The width and depth of the keyway are determined by the size and shape of the cutter and the depth of cut.

This type of machine can be operated manually, by moving the cutting tool along the tracks, or it can be operated by CNC (computer numerical control) and can be programmed to cut keyways of specific dimensions and shapes in a precise and efficient manner.

Keyseating milling machines are used in a variety of industries, including automotive, aerospace, and heavy equipment manufacturing, where precision keyways are needed for shafts and other cylindrical parts.