Patent ID: 8257633

Claim:
A method of forming a rotor comprising: providing a mold with a profiled helical bore by: disposing a first body with a profiled helical outer surface into a longitudinal bore of a second body; filling a void between the profiled helical outer surface of the first body and the longitudinal bore of the second body with a second cast material in a fluid state; solidifying the second cast material to impart the profiled helical bore into the second cast material; and removing the first body from the profiled helical bore in the second cast material to create the mold with the profiled helical bore; inserting a resilient tube into the profiled helical bore; conforming the resilient tube to the profiled helical bore; disposing a core within the profiled helical bore; filling a void between an outer surface of the core and the resilient tube in the mold with a cast material in a fluid state; solidifying the cast material to impart a profiled helical outer surface into the cast material and into the resilient tube; and removing the mold to present a rotor with the core surrounded by the cast material which, in turn, is surrounded by the resilient tube.