Photos by Dee and Brooke Williams
A casting pour at a prop shop foundry is a brief but dramatic event. Workers appear otherworldly in their protective gear. The crucible glows red hot. Escaping gases flare up an intense yellow, creating plenty of smoke and odor.
It’s the visual highlight of the manufacturing process at Ellis Propeller but neither the beginning nor the end.
The process begins with a small glued stack of plywood. Mold plugs for all but outboard and outdrive props are CNC-routed from plywood stacks. A single blade plug and its hub will go into a sand-mold box with separate partitions for each blade of the final prop. These partitions have a lower mold section and one above the blade. Workers carefully craft the plug surface while a hardening agent sets up the sand to concrete-like hardness. It takes a good part of a day to craft a set of smooth molds — a significant mistake will render the casting unusable.
Off to one side, foundry workers fire up the crucible to melt the propeller bronze. The magnesium-bronze alloy used for the props seen here needs to come up to 1,900 F. After the crucible is warmed, ingots are gradually added during the day, and with a final temperature check they are ready for a late afternoon pouring.
After cooling overnight, the props are inspected, and the finishing process begins. First, the hub is centered and the shaft hole drilled using CNC equipment. After that, all work at Ellis is done by hand. The hub’s face is machined to specification on a lathe, and workers then grind castings to shape, constantly checking balance. These workers have detailed specifications for each propeller, so a rough casting that shows the coarse grain of its sand mold and some irregularities will become a smooth, shaped surface. Measurement checks deal with millimeter tolerances. Lastly, the prop is polished and ready for shipment.
For more information, contact Ellis Propeller: (904) 354-8233.
November 2013 issue