Method of specifying position to create fillet curved surface

A method of specifying a position to create a fillet curved surface at a boundary defined between two curved surfaces of a compound curved surface, by producing numerical control data for cutting the compound curved surface using an apparatus which generates said numerical control data, said method comprising the steps of;

• finding lattice points of the compound curved surface, through which a cutting tool passes, and normal vectors of said lattice points, based on input curved surface information and cutting information input to said apparatus;
• inputting, to said computer, input information for one of inserting a concave fillet and inserting a convex fillet into the boundary defined between said two curved surfaces;
• instructing said cutting tool to create said concave fillet at the boundary to which normal vectors of said two curved surfaces are both directed when said input information specifies a concave fillet;
• and
• instructing said cutting tool to create said convex fillet into the boundary defined by two curved surfaces to which neither of said normal vectors of said two curved surfaces are directed when said input information specifies a convex fillet.