This steel master (O-1 steel) is used to make a silicone rubber mold. The steel master is made 15% bigger than the cast prop to compensate for shrinkage. The steel master has blades which were silver soldered into the prop hub. High temperature silver solder is used & the prop is hardened while being silver soldered. After hardening in oil, the prop is tempered blue to a spring temper. The blade is tested at the lake before casting investment wax copies.
