a structure and method of assembling a rotor assembly is provided , without the use of a rotor steel hub . the method comprises forming first , second and third lamination stacks by stacking individual rotor laminations together . the first , second and third lamination stacks are cast to lock the individual rotor laminations together . the rotor laminations in the first , second and third lamination stacks have a generally ring - like shape with a variable inner diameter and a substantially common outer diameter . the rotor laminations in the first , second and third lamination stacks have substantially the same outer diameter , whereas the rotor laminations in the second lamination stack have a substantially larger inner diameter than the first and third rotor laminations . the elimination of the hub results in reducing total cost and manufacturing cycle time , and in improved features , performance and efficiency of the rotor assembly .