Examples are disclosed herein that relate to creating undercuts and other complex geometries in an injection molded article. One example provides a method of forming an injection molded article comprising an undercut structure, the method comprising inserting an insert piece into a mold for forming the molded article, the insert piece comprising sacrificial material, injection-molding the molded article, thereby incorporating the insert piece into the injection molded article, and machining the insert piece to form the undercut structure from the sacrificial material.