Milling machine and method of cutting a keyway

A method of cutting a keyway in a shaft using a milling machine while the shaft is on site in a piece of machinery, said method comprising the steps of providing the milling machine comprising a guiding base forming a guideway, a clamping device for clamping the guiding base on the shaft, a guided base being mounted on the guiding base and being configured to be moved on and guided by the guideway, and a cutting unit being mounted on the guided base and being adapted to hold and rotate a milling head, wherein the guided base and the cutting unit mounted on the guided base together are configured to be longitudinally displaced on the guiding base and the cutting unit is configured to be locked in various lateral positions, transverse to the direction of longitudinal displacement, on the guided base, and the cutting unit is mounted to be swingable about an axis so as to be laterally displaced, clamping said guiding base on the shaft and cutting the keyway with a milling head by moving said cutting unit with its, milling head along the guideway and thereby along the shaft, wherein a milling head is used that has a diameter smaller than the width of the keyway and the keyway is cut in more than one sweep and laterally displaced on the guided base between the milling sweeps.