Abstract: A variable pitch propeller assembly is disclosed for a power boat. Three blades are mounted on a housing carried by the propeller shaft. Each blade has an axle received in the housing. Each axle has a slot receiving a dowel carried in the housing so the blade can rotate about 5.degree. between two pitch positions. A centrifugally-operated, spring biased latch carried in the housing locks the shaft in each pitch position. The blade is released from the latch by a predetermined change in the hydrodynamic force acting on the blade surface. The propeller shaft is connected to the propeller assembly by three plastic keys which shear to permit the propeller assembly to spin with respect to the propeller shaft when the propeller assembly strikes a predetermined resistance, such as a rock or the like.

Abstract: An investment casting process employs a low-cost plastic pattern manufactured by machining. A mold is cast around the plastic pattern following which the pattern is removed from the mold to leave a mold cavity which molten metal or the like may be poured to produce a finished part. Reusable plastic patterns may be formed by casing silastic rubber. The silastic rubber patterns may be mechanically separated from the mold without damaging the pattern.

Abstract: A rotary drill bit for drilling wells in earth formations is produced by a casting technique using a plastic foam, combustible casting form. The bit includes a tapered drill body having a plurality of passageways therein which form jets for introducing liquid between the earth and a plurality of selectively arranged, cutting members extending outwardly from the drill body. The combustible form is molded in a shape substantially identical to that of the drill body. The cutting members are mounted on the form in the selective arrangement thereof, and the assembly of the form and cutting members are then coated with a mold material to form a mold body. A cavity is created in the form for receiving a molding mandrel which defines the longitudinal passageway of the completed bit. Molding pins are introduced through the mold body into the mandrel to precisely hold the mandrel relative to the mold body. The cutting members are precisely held by the mold body after the form is removed by combustion.