A deep groove, for example a groove in a rotor for a generator or turbine, can be formed in the rotor blank in only two sequential milling cuts, and wherein each milling cut, utilizing a single rotary milling cutter, carries out at the time both coarse cutting of the groove and finish cutting, for surface smoothing, of the coarse cut along the inner surfaces of the groove. The milling cutter carries cutter chips (22, 23, 25; 44, 46) retained against chip seats (27) in cutter chip cartridges (21, 210) wherein at least some of the cutter chips have at least one end cutting edge forming a main or coarse cutting edge (33, 35, 42; 45, 47) exposed from the respective cartridge and the tool body (13, 130) for main or coarse cutting. Some cutter chips located on the cartridges also have at least one fine or finish side cutting edge (36, 49) exposed for cutting. The chips having the at least one main cutting edge cut, each, a portion of the width of the grooves, so that the sequential chips and sequential cartridges coarsely cut the entire width of the groove. The chips having the fine or finish cutting edges in at least one of the sequential cartridges have outwardly directed fine cutting edges (36, 49) located adjacent the main cutting edges (35), so that the combined operation of the cutting edges of the chips in sequential cartridges, with the main or coarse end cutting edges and the fine or finish side cutting edges on the respective chips, will generate a complete coarse and finish cut in the workpiece in one operation. Two such tools can be used with different chip configuration to form stepped grooves of, for example, an overall depth of about 22 cm, with a groove width at the widest point of about 4 cm.
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