Propellers are a vital component of both remote control (RC) boats and planes. When making a mould for propellers, selecting the propeller that will serve as a master is very important. The closer to perfect that the master propeller is, the better the copies made will be. Thoroughly prepare and polish the master propeller before beginning to make the mould.
Sand the hub on the prototype propeller so that it gently tapers away from the centre line of the propeller. This will help to make sure the propeller does not stick in the mould. Apply wax to the entire propeller. Cut a rectangular piece of plastic laminate or aluminium to form the base of the mould box. It should be slightly wider and longer than the prop that will be moulded. Cut two rectangular pieces of plastic laminate or aluminium to form the sides of the mould box. These pieces should be slightly wider, longer and taller than the propeller that will be moulded. Cut two identical pieces of plastic laminate or aluminium to form the ends of the mould box. Again, they should be slightly wider and taller than the prop being moulded. The dimensions of the mould box do not need to be exact. The finished box must be large enough to easily fit the propeller and moulding compound.
Drill a hole in the centre of the base. This hole must be large enough to accommodate the steel prop shaft pin. Insert the steel rod in the hole. Place the propeller on the steel rod with the front of the prop facing up. The bottom of the prop should be at least 1/8 inch from the base piece. The prop should be parallel with the base.
Knead the modelling compound until it is soft. Place the compound under the prop, making sure that the compound isn't deforming the propeller blades. Smooth the modelling compound until it is precisely at the edge of the blades. The compound must not come above the blades. Apply at least four coats of wax to the propeller and the modelling compound. The accretion of wax will help to smooth out visible imperfections such as fingerprints. Apply at least four coats of was to the previously cut pieces of plastic laminate or aluminium.
Apply a coat of PVA to the propeller, modelling compound and the pieces of plastic laminate or aluminium. Let the PVA dry before proceeding. Assemble the pieces of plastic laminate or aluminium to form an open-topped box. Mix the epoxy resin with the catalyst. The amount used will depend on the size of the propeller being moulded. Add twice as much aluminum oxide powder to the mixture as epoxy resin and catalyst. Let the mixture sit so that air can escape. This process can be aided by gently tapping the container on a hard surface.
Brush the resulting mixture over the propeller and modelling compound. Pour the rest of the mixture into the box. Place the box on a level surface and let sit for at least 24 hours. Remove the clamps and carefully remove the side pieces of the box. Remove the base, and then carefully remove the modelling compound. Clean everything and coat all surfaces with at least four coats of was. Apply a layer of PVA to all surfaces, paying special attention to the seam line.
Apply a coat of wax to the plastic laminate or aluminium panels. Apply a coat of PVA to the panels and let dry. Assemble the side and end pieces of the box, using the first of the mould in place of the base piece. Clamp the pieces together, making sure there are no gaps. Mix another batch of epoxy, catalyst and aluminum oxide in the same proportions as before. Let the mixture sit so that air can escape. Gently tap the container on hard surface to allow air bubbles to come to the surface. Brush the bottom half of the mould with the mixture, making sure to brush into all crevices. Pour the rest of the mixture into the mould. Place it on a level surface and let sit for at least 24 hours.
Remove the laminated plastic or aluminium panels. Run a thin putty knife along the seam to open up the mould. Strike one side of the mould on a hard surface. Rotate the mould and strike the next side on the hard surface. This will break the two halves of the mould free and render it ready for use.