Multi-part combustible casting pattern having bend-resistant glue-less joints

Claim 1

A multi-part combustible pattern for foundry use, comprising a plurality of pattern parts formed of material which is combustible under a charge of molten metal to be cast and which in compression is partly elastic, said plurality of parts having abutting mating surfaces and being formed to shapes which, when assembled at such mating surfaces, make up a desired pattern form, characterized in that a first of said parts has in its mating surface a groove whose cross-section is generally of reverse taper, said groove including a partially cylindrical portion formed on an axis perpendicular to the mating surface of said part, and whose diameter equals the maximum width of said reverse taper cross-section of the groove, further characterized in that a second of said parts has, projecting from its said mating surface, a reverse taper tongue compressively insertable within the reversed taper of said groove, the said mating surFace of said second part being of sufficient extent to close off the partially cylindrical groove portion by sealed abutment against the said mating surface of said first part, whereby on such assembly of the pattern, said tongue-and-groove provisions present no surface irregularity.