A new method to produce optimal castable topology designs with optimal parting surfaces is presented. The method is based on parameterizing the design domain and is suitable to be used with gradient-based topology optimization methods. The proposed method takes into consideration irregular meshes commonly used in industrial applications. It also takes into consideration minimum member sizes that are needed for manufacturability and to control the checkerboard phenomena. The method is discipline independent and was tested on linear static and dynamic problems. The method is very efficient as it reduces the number of design variables and does not need to add additional constraints to reflect the manufacturing requirements. The manufacturing requirements are built in a parameterization of the design variables. The development was motivated by the need for generating structural design proposals that could be manufactured with minimum changes. The proposed method was implemented in the GENESIS program and examples that reveal its usefulness are included.