A computer implemented method for providing a three-dimensional model and generating a toolpath specification for manufacturing of objects that employs a 2.5-axis subtractive manufacturing process, the method comprising: obtaining, by a computer aided design program, a design space for an object to be manufactured and one or more design criteria including at least one manufacturability constraint for the object; performing, by the computer aided design program, a boundary-based generative design process to produce a generative model for the object using the one or more design criteria, wherein the boundary-based generative design process tracks an outer shape boundary of a solid part of the object and moves the outer shape boundary to satisfy the at least one manufacturability constraint for the object, wherein the at least one manufacturability constraint causes at least one shape derivative to be applied to the outer shape boundary during the boundary-based generative design process to guide outer shape changes for the generative model toward discrete height layers corresponding to the 2.5-axis subtractive manufacturing process, wherein the at least one shape derivative defines a shape change velocity to be used to update the outer shape boundary to satisfy the at least one manufacturability constraint for the object; and providing, by the computer aided design program, a three dimensional model in accordance with the generative model, for use in manufacturing a physical structure corresponding to the object using one or more computer-controlled manufacturing systems that employ the 2.5-axis subtractive manufacturing process, wherein the three dimensional model includes flat areas resulting from the discrete height layers, wherein providing the three dimensional model comprises generating a toolpath specification for manufacturing of the object using the 2.5-axis subtractive manufacturing process, wherein the toolpath specification is generated using the three dimensional model. obtaining, by a computer aided design program, a design space for an object to be manufactured and one or more design criteria including at least one manufacturability constraint for the object; performing, by the computer aided design program, a boundary-based generative design process to produce a generative model for the object using the one or more design criteria, wherein the boundary-based generative design process tracks an outer shape boundary of a solid part of the object and moves the outer shape boundary to satisfy the at least one manufacturability constraint for the object, wherein the at least one manufacturability constraint causes at least one shape derivative to be applied to the outer shape boundary during the boundary-based generative design process to guide outer shape changes for the generative model toward discrete height layers corresponding to the 2.5-axis subtractive manufacturing process, wherein the at least one shape derivative defines a shape change velocity to be used to update the outer shape boundary to satisfy the at least one manufacturability constraint for the object; and providing, by the computer aided design program, a three dimensional model in accordance with the generative model, for use in manufacturing a physical structure corresponding to the object using one or more computer-controlled manufacturing systems that employ the 2.5-axis subtractive manufacturing process, wherein the three dimensional model includes flat areas resulting from the discrete height layers, wherein providing the three dimensional model comprises generating a toolpath specification for manufacturing of the object using the 2.5-axis subtractive manufacturing process, wherein the toolpath specification is generated using the three dimensional model.