A method of generating an article comprising: receiving a representation of the article as an initial piecewise cubic Bézier curve in 2-dimensions, or in 3-dimensions; receiving one or more constraints for the article associated with a parameter of the article; determining a maximum permissible curvature of one or more parts of the article from the constraints of the article, wherein the parameter of the article comprises a physical property of a material from which a part of the article is to be manufactured; measuring the maximum curvature of the one or more parts of the article in the received representation; comparing the measured maximum curvature with the maximum permissible curvature determined from the constraints of the article; and, if the measured maximum curvature of at least one of the one or more parts exceeds the determined maximum permissible curvature, providing an error indication; or if the measured maximum curvature of each of the one or more parts does not exceed the determined maximum permissible curvature, storing the received representation for the article; inputting the stored representation for the one or more parts of the article to a computer controlled machine; and replicating the parts of the article in a material, using the computer controlled machine, wherein the method further comprises in response to the error indication, receiving modifications to the design representation, or to the constraints; and, repeating from the comparing step, or from the determining step accordingly, until a compliant design is achieved, or the design is rejected. receiving a representation of the article as an initial piecewise cubic Bézier curve in 2-dimensions, or in 3-dimensions; receiving one or more constraints for the article associated with a parameter of the article; determining a maximum permissible curvature of one or more parts of the article from the constraints of the article, wherein the parameter of the article comprises a physical property of a material from which a part of the article is to be manufactured; measuring the maximum curvature of the one or more parts of the article in the received representation; comparing the measured maximum curvature with the maximum permissible curvature determined from the constraints of the article; and, if the measured maximum curvature of at least one of the one or more parts exceeds the determined maximum permissible curvature, providing an error indication; or if the measured maximum curvature of each of the one or more parts does not exceed the determined maximum permissible curvature, storing the received representation for the article; inputting the stored representation for the one or more parts of the article to a computer controlled machine; and replicating the parts of the article in a material, using the computer controlled machine, storing the received representation for the article; inputting the stored representation for the one or more parts of the article to a computer controlled machine; and replicating the parts of the article in a material, using the computer controlled machine, wherein the method further comprises in response to the error indication, receiving modifications to the design representation, or to the constraints; and, repeating from the comparing step, or from the determining step accordingly, until a compliant design is achieved, or the design is rejected. <EOS>