The invention relates to a method for producing heat-resistant casting moulds from mould materials, especially from moulding sand containing a binding agent, or for producing an inner contour of models or prototypes consisting of plastic, graphite, derived timber products or other millable materials. Large volumes and deep gravures are often obtained, especially during the machining of moulds for the rapid production of prototypes of cast materials. In order to increase the efficiency of the inventive method, in a first step, blocks of mould material are produced in such a way that a dimension thereof corresponds to a mould cavity depth which typically measures up to between 300 and 400 mm. The inner contour of the mould is then produced in such a way that it has an oversize having a contour which is close to the contour of the inner wall of the mould cavity, using a roughing tool (4) having an effective cutting diameter of between 12 and 35 mm. The mould cavity is then machined by milling the oversize material, following the contour, using a finishing cutter (3) having a diameter-length ratio of between 1:10 and 1:30.