Propeller Fabrication Details

By S.E.Moore -- Revised June 25, 2005

("McM" refers to McMaster-Carr catalog numbers)

A Rivabo 100mm 4-blade brass propeller was used as a master model to create a mold from which polyurethane duplicates could be cast.

First Durham's water putty was used to fill the undercuts of the prop. Minor imperfections in the putty were filled with purple jeweler's wax.
The prop was mounted in a 4" PVC cap using the 5mm tapped hole in its center hub.
1stpour The prop and putty filler were sprayed with mold release, and Tap polyurethane RTV poured flush with the top of the putty.
1stopen The RTV was allowed to cure for 48 hours after which the putty filler was removed.
2ndpour Risers made from small dowels were added to the high point of each blade, and a pouring cup cemented to the center hub. Mold release was sprayed on the cured RTV and model, and a second batch of RTV was poured in to fill the cap.
2ndopen After another 48 hours the mold was opened, and the dowels and pouring cup removed. The mounting screw was removed, and the brass original lifted out.
The mounting screw was reinstalled -- this time to act as a mold for the internal threads of the cast prop. All internal surfaces were coated with mold release, and the mold reassembled.
moldopen Approximately 2 oz. of Tap Quik-Cast polyurethane casting resin were mixed and poured into the mold. After about 1 hour the mold was opened to reveal the cast prop.
rawprop The mounting screw was removed, and the new prop lifted out.

Flash and imperfections from the risers and pouring cup were removed with hand tools.
4props Multiple propellers can now be cast from the reusable mold.