Abstract

Method of making a pattern for a prototype mold including making a cardboard composite pattern which simulates a prototype part to be molded as the latter is disposed in die position, the method including building up a box-like structure of glued-together cardboard templates and cardboard surface parts, the templates upstanding from a grid base in accordance with a design drawing for the prototype part, the surface parts providing the exterior surface for the cardboard composite pattern save for the curved surfaces thereof, the curved exterior surfaces being imparted to the cardboard composite pattern by the following steps: (i) coating the interior of the box-like structure with a two-part foam material that sets up into a rigid mass; (ii) thereafter cutting the surface parts along a tangent line and where else curvature is needed for the cardboard composite pattern to expose the hardened foam substrate and edges of the surface parts; and (iii) covering such exposed exterior surfaces with a pliable material and shaping same into the exterior curvature needed for the cardboard composite pattern, the cardboard composite pattern duplicating the exterior surfaces of the prototype part to within tolerances of plus or minus one millimeter.