Positive retention features are provided on an actuator of a magnetic disk drive thereby increasing the structural rigidity of the actuator in attachment of a voice coil to the actuator. The positive retention features are defined by a plurality of protrusions having compound curved shapes including reverse or inward facing edges. The natural tendency of thermoplastic resin to shrink during cooling is used to an advantage in enhancing the rigidity of the connection between the voice coil and actuator body. The compound curved shapes of the positive retention features allows shrinkage of the thermoplastic resin in multiple directions around the features thereby maintaining desired actuator stiffness.