Aiming at the geometrical features of different containment relationships in Rapid Prototyping (RP), a general method of achieving the RP layer’s cusp distribution of the positive, negative and mixed tolerance is proposed to meet the part’s different applications. The procedure is executed by projecting the current and the next section of the CAD model onto a horizontal plane, computing the union and the intersection of the sections to get the outer and the inner boundary, and then blending the boundaries using a rotary vector through a proper inner point in the intersection to achieve the current layer’s scanning contour. The method can realize the layer’s cusp distribution of the mixed tolerance with unequal cusp height, expanding the connotation of the mixed tolerance.
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