A method comprising: obtaining a design space for a modeled object, for which a corresponding physical structure is to be manufactured using a 2.5-axis subtractive manufacturing process, one or more design criteria for the modeled object, and one or more in-use cases for the physical structure wherein the 2.5-axis subtractive manufacturing process includes a 2.5 dimension that refers to a plane that is parallel to an x-y plane with respect to machining, but with a different z-coordinate, iteratively modifying a generatively designed three dimensional shape of the modeled object in the design space in accordance with the one or more design criteria and the one or more in-use cases, wherein the iteratively modifying employs a density-based representation of the generatively designed three dimensional shape of the modeled object, and the iteratively modifying comprises adjusting the density-based representation of the generatively designed three dimensional shape in accordance with a milling direction of the 2.5-axis subtractive manufacturing process in at least two iterations of the iteratively modifying, the adjusting comprising collecting different milling depths associated with different subsets of individual elements in the density-based representation of the generatively designed three dimensional shape, grouping the different milling depths into respective ones of three or more discrete layers, each of the three or more discrete layers being perpendicular to the milling direction of the 2.5-axis subtractive manufacturing process, and changing density values for at least a portion of the individual elements in the density-based representation such that a single milling depth is produced for each of the three or more discrete layers; and providing the generatively designed three dimensional shape of the modeled object for use in manufacturing the physical structure using one or more computer-controlled manufacturing systems that employ the 2.5-axis subtractive manufacturing process. obtaining a design space for a modeled object, for which a corresponding physical structure is to be manufactured using a 2.5-axis subtractive manufacturing process, one or more design criteria for the modeled object, and one or more in-use cases for the physical structure wherein the 2.5-axis subtractive manufacturing process includes a 2.5 dimension that refers to a plane that is parallel to an x-y plane with respect to machining, but with a different z-coordinate, iteratively modifying a generatively designed three dimensional shape of the modeled object in the design space in accordance with the one or more design criteria and the one or more in-use cases, wherein the iteratively modifying employs a density-based representation of the generatively designed three dimensional shape of the modeled object, and the iteratively modifying comprises adjusting the density-based representation of the generatively designed three dimensional shape in accordance with a milling direction of the 2.5-axis subtractive manufacturing process in at least two iterations of the iteratively modifying, the adjusting comprising collecting different milling depths associated with different subsets of individual elements in the density-based representation of the generatively designed three dimensional shape, grouping the different milling depths into respective ones of three or more discrete layers, each of the three or more discrete layers being perpendicular to the milling direction of the 2.5-axis subtractive manufacturing process, and changing density values for at least a portion of the individual elements in the density-based representation such that a single milling depth is produced for each of the three or more discrete layers; and collecting different milling depths associated with different subsets of individual elements in the density-based representation of the generatively designed three dimensional shape, grouping the different milling depths into respective ones of three or more discrete layers, each of the three or more discrete layers being perpendicular to the milling direction of the 2.5-axis subtractive manufacturing process, and changing density values for at least a portion of the individual elements in the density-based representation such that a single milling depth is produced for each of the three or more discrete layers; and providing the generatively designed three dimensional shape of the modeled object for use in manufacturing the physical structure using one or more computer-controlled manufacturing systems that employ the 2.5-axis subtractive manufacturing process.