Geometric ingenuity transforms metal into expression

November 2012 - A design dreamed up by inventor Chuck Hoberman, founder and president of Hoberman Associates Inc., New York, the “Hoberman Sphere” is a popular children’s toy, as well as an artful display for museums and private collectors.

Based on an icosidodecahedron, a polyhedron with 20 triangular faces and 12 pentagonal faces, the sphere folds to a fraction of its size then expands smoothly and continuously. Hoberman invented and patented his original sphere in 1990. Today, using aircraft quality aluminum, the team at Hoberman Associates builds each sphere for a custom installation. Recently, the team erected a sphere dubbed Nouaison, French for first growth, in Bordeaux, France, at the Château Smith Haut Lafitte. 

Hoberman Associates outsources the machining of parts to CNC machining centers. “We send them detailed drawings for the parts we want and we also do some in-house machining,” Hoberman says. “We specify the parts, send them out for finishing and closely monitor all the fabrication and finishes as it goes along and everything comes in, along with a whole series of industrial fasteners and connectors. Our team puts these parts together with industrial fasteners and connectors and tests the spheres in our space. If it’s too large, we rent a space and send a crew to install the piece.”

Building the bubble

According to Matt Davis, vice president of engineering at Hoberman Associates, the visible portion of the sphere is made using tempered, high-strength, heat-treated aluminum. The bearings are plastic. The reason for the aluminum-only approach is to avoid the galvanic reaction that occurs when different metals come in contact with weathering elements, such as seawater, resulting in rapid rusting. “We wanted to make sure it was 100 percent aluminum with no steel in contact with the aluminum, otherwise, they start to corrode quickly. It’s a problem engineers have to consider when working with exterior installations across the board,” Davis says.

The exterior aluminum parts are 100 billet CNC machined, “so there’s not a drop of welding,” Davis adds. “Hands rarely touch it.” The aluminum is bright dipped, a form of chemical polishing, and a clear anodized finish is applied as a hard coat. The aluminum itself is bright-dip anodized to give a sparkling coloration and look, says Hoberman. 

The team created a customized machining pattern to create grooves on the surface of the 6061-T6 aluminum with 90 degree milling angles, which were flat at the bottom. “The sphere is an assembly of hundreds and sometimes thousands of machined parts connected together, not unlike a big construction kit,” Hoberman says. 

“If you don’t anodize the aluminum, it will oxidize and become a flat or matte full gray,” Davis says. “We seal the surface to keep it looking exactly the way it did when it popped off the CNC machine.” Nouaison shipped in four pieces: the sphere, main piston, actuation system and support structure.

“Installation itself was fairly simple, [consisting of] anchoring the metal to the ground and putting in a dozen bolts,” Davis explains. “The biggest technical challenge at that point for this installation within the winery involved putting an 8-in. hole through the roof of the wine cellar and making sure it wouldn’t leak.”

The structure within the building that’s hidden from the average viewer is made completely from steel. “We rely heavily on laser-cut steel for the structural component of the installation,” Davis says. “We create the jigsaw puzzle from 1/8-in. steel plate. To assemble, we MIG weld it together. It’s 100 percent digitally designed and assembled by hand.”

“With the vineyard surrounding the installation, we took into consideration the woods surrounding the terrace, the rolling clouds going by, and wanted to create an object that would play with reflections of nature and have a sparkle to it,” Hoberman says. “The color scheme gives an optical sensation.” FFJ