A Magnetic Gear Modulator (MGM) of a Concentric Magnetic Gear (CMG) is manufactured by injection molding a modulator cage over angularly spaced apart MGM pole pieces made of a magnetically conducting material. The pole pieces are initially connected by a support ring, or held by a fixture. The modulator cage is preferably a thermally conductive strengthening fiber filled plastic, a carbon fiber plastic, a carbon fiber filled plastic material, a glass material, or a high performance composite plastic molding material. After molding, the outer and/or inner portions of the molding material, and support ring if present, are machined away preferably exposing both inner and outer faces of the pole pieces embedded in the modulator cage. An MGM made using injection molding over a connected support ring and pole pieces reduces cost, and a carbon fiber plastic modulator cage increases strength.