Patent ID: 8418366

Claim:
An internal gear manufacturing method comprising: providing a thin, long tubular mold; providing a non-metallic solid core having a gear portion in a shape of an external gear, said non-metallic solid core has a length equal to that of said tubular mold; positioning said non-metallic solid core inside and longitudinally along said tubular mold so as to provide a uniform space between the tubular mold and the non-metallic solid core; pouring a molten metal material under a temperature higher than a melting point thereof into the space between said tubular mold and said non-metallic solid core; letting said metal material resolidify in said mold containing said core; and removing said solid core by pulverization or dissolution after resolidification of said molten metal material, wherein said resolidified metal material with the solid core removed forms an internal gear structure.