All of our smaller cabinet pulls and many of our slim elongated handles are cast in solid bronze or stainless steel but other pieces, including the Grapevine Heroic Pull are cast using a hollow shell to create a hollow casting. The complexity of the design and the weight of the alloy determine whether the piece is to be cast as a solid handle. For example, the ergo extended pull is 35” and the Grapevine is 42” but the Ergo pull would be prone to warping if it were a hollow casting but being a little slimmer when cast is a manageable 10.5 lbs. By comparison, the Grapevine handle is considerably longer but because it is hollow cast is only 1lb heavier.
In a previous post I described how a wax pattern is made and how the location and number of wax runners and gates determine how the wax and subsequent bronze will flow. Whether the casting is a success will also depend on how the piece is shelled and how the shell is subsequently removed.
3 Wax Sections - Access Holes Added to Each So That The Hard Shell Can Be Removed From the Inside of the Castings
The wax replicas are repeatedly dipped into a fine ceramic slurry. The slurry needs to be fine to capture the detail on the surface of the wax replica and enough coats need to be built up to form a strong wall casing around the wax. The outer layers of the slurry are reinforced with coarser fibers that help create a stronger wall. The shell is then fired to create an extraordinarily strong casing and the wax is removed leaving the shell hollow and ready to receive molten metal. Once cast the shell will be broken off and the casting will be ready to finish.
The Grapevine handle is cast in 3 sections with 3 hollow waxes making 3 bronze castings that are welded together to create one handle. As the entire inside and outside surface of each wax section will be encased in a ceramic shell, we created holes or patches in the wax as access points. These holes or patches were also shelled and then cast in bronze. After the bronze castings were poured, we were able to remove the hard shell from inside the casting by sandblasting the interior through the access holes. The bronze patches or plugs are then welded onto the casting the 3 pieces are welded together and the welding joints are tooled by hand to create a seamless piece.
Each wax section of the Grapevine handle required 2 to 3 patches.
Access Holes Created In the Wax - The Removed “Patch” Is Cast In Bronze - Patch Seamlessly Welded In Place