A method for manufacturing a main rotor for a generator is provided. The method includes printing at least part of a rotor shaft by a three-dimensional printing process. The step of printing at least part of the rotor shaft includes printing a plurality of closed outlets and a plurality of open outlets. A rotor core is printed by the three-dimensional printing process. The step of printing the rotor core includes printing a plurality of liquid coolant conduits that extend through the rotor core and fluidly connecting the plurality of liquid coolant conduits to the plurality of closed openings.