CASTING BRONZE PINTLES

For the Croatian fishing boat "Batana"

Article by James Thomas

In August of 2022 my boat neighbor, Rick Meyers, at Swantown Marina in Olympia invited me to join him volunteering for the day at the Gig Harbor BoatShop—a historic boathouse rescued from gentrification by the citizens of Gig Harbor, Washington. On Saturdays the BoatShop hosts a day working with Tom Regan, a veteran boat and oar builder, now retired, who has done business as Grapeview Point Boat Works. 

As it happens, the day I first visited, Tom was planning to cast bronze hardware for a historic Croatian fishing boat being built by local Croatians and Croatian-Americans honoring some of the original families who settled and fished out of Gig Harbor. To hold the transom-hung rudder of the boat, gudgeons and pintles were needed and it was these parts Tom and the volunteers set about making. I’d seen videos of the casting of large parts at the Port Townsend Foundry, but participating in the process on a much smaller scale was fascinating and convinced me to make the Gig Harbor shop a regular destination on Saturdays.

The photos that follow give an outline of the casting process. Tom loaned his equipment for the process. It consisted of the wood boxes, called flasks that hold patterns, the casting sand and oil, a propane fired furnace, a crucible vessel for melting scrap bronze in the furnace, and tools for extracting the crucible from the furnace including safety gear. During previous Saturdays, the volunteers had fashioned wood versions of the gudgeons and pintles that would serve as patterns for use in casting the bronze hardware. 

Breaking up the foundry sand with a mixer

The wooden pintle pattern ready for embedding in the casting flask

The lower “drag” flask on the right, the upper “cope” flask on the left

The wooden pintle pattern  is dusted with release compound to make it easier to extract from the flask later.

The drag flask with the pattern fully embedded in packed sand

Placing the upper cope flask on top of the drag flask.  Note that wood blocks register the upper and lower flasks to a fixed position. The upper flask will be filled with sand hard packed around a sproul, a tube which, when removed, becomes the pathway for the molten bronze into the negative space left when the pattern is removed from the lower drag flask. Popsicle sticks are also placed embedded at the opposite end of where the sproul is to provide vents for trapped air to escape as bronze fills the mold void.

The cope flask set onto the drag flask. Next step (not shown) is to locate the pathway for the bronze to flow into the mold (called a sproul) and two vents to allow movement of molten bronze through the negative space of the mold cavity

The lower “drag” flask with the pattern being readied for careful removal from the sand filled flask. 

Before the pattern can be removed from the lower flask, the upper flask must be removed and placed to the side.  Similar to the lower flask, the upper flask is filled with packed foundry sand with vent holes created by sticks and a pathway for the molten bronze created by a conical sproul that rests on the pattern in the lower flask.  A dam is formed around the sproul to receive the molten bronze pour.  After being well packed in, the vent sticks and sproul are removed leaving passages through the packed sand down to the lower flask and mold cavity.

The lower or “drag” flask with the pattern removed creating the void space for bronze casting. The upper “cope” flask can then carefully be placed back on top of the lower flask.

The furnace, the crucible that holds the bronze for melting in the furnace, and the completed flasks ready to receive molten bronze.

After cooling the cast pintle is removed from the flask. Note the bronze “mushroom” where the sproul hole was located and the bronze spikes where vents were located in the mold. These are cut off in the finishing process.  

Here’s the fishing boat, named Batana, that will use the bronze rudder hardware we cast in the previous photos.

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