After the shaft has been inserted into the die-cast copper rotor, a machining operation ensures that the rotor OD, the bearing journals and the shaft OD are all concentric. Similar to the machining of aluminum rotors, it is important that the cutting tools be kept sharp, to prevent the edges of the lamination from smearing. Smearing will increase the electrical contact between adjacent laminations, which can significantly increase eddy current losses in the motor. As copper rotors are usually used in high efficiency applications, such an increase in eddy current losses will be especially detrimental to performance.
