“For me, figuring out how to build things is more interesting than designing them.” Listening to Shawn Keller talk about wonky topics such as “fabrication tolerance modeling” can be fascinating. He clearly loves what he does; you can see it in the way he lights up when discussing different fabrication approaches. “Problem solving is the fun part.” His father, Charles, started CW Keller in 1974 in the basement of his house. The younger Keller grew up in his father’s shop and was always surrounded by tools. His passion for problem solving must run in the family.
I met Keller in 2008 while working on the Boston Harbor Islands Pavilion on the Rose F. Kennedy Greenway, long before digital fabrication was trendy. Along with Turner Construction, our firm was excited by the challenge of building this unconventional concrete structure — the first permanent structure on the Greenway.
The pavilion comprises two poured-in-place concrete roofs with complex curves. The roofs are designed to shed water from an upper roof onto a lower roof, and end in a tightly pinched scupperlike form that flows into a sculpted stone catch basin, much like the spout of a pitcher. We were interested in making the concrete roof structure appear as thin and lightweight as possible. We were also set on the roof being a poured-in-place structure to achieve a monolithic reading, as opposed to precast concrete composed of multiple pieces. This presented several technical challenges. We needed a digital fabricator, and that’s where Keller came in.
CW Keller is a shop known for its early proficiency in linking Rhino modeling with computer numerical control (cnc) milling. His shop was also getting good at forming machined curved surfaces out of layers of plywood. Keller was psyched about taking our 3-d model and figuring out how to divide it into individual panels that could be assembled in the field to form the continuous complex curved surfaces of the two roofs.
The underside surface of the roof was what we cared most about — it had to be as smooth and seamless as possible. Keller recognized that the plywood had to be extra thin (¼ inch) to take the shape of the curvature; however, the tightly pinched scupper went beyond its bending tolerance. This is where Keller combined several vertically stacked plywood sheets and carved them to the shape described in the 3-d model. A series of wood ribs were then created to support the plywood sheets and take up the difference between the bottom of the curved surface and the top of formwork staging.
The design-fabrication collaboration allowed for a level of scrutiny and coordination that included defining the seam layout and identifying the location of screws to form a pattern. Although pouring the concrete in a single pour (yes, you have only one shot!) had its own challenges, I would argue that the formwork was the key factor in making it all come together.
Keller has further refined this fabrication tolerance modeling to much larger-scaled projects, including a concrete house designed by Steven Holl and the Sixth Street Viaduct for the City of Los Angeles designed by Michael Maltzan and hntb. What is most amazing about Keller is his ability to take a simple concept and think about the appropriate medium (plaster, concrete, wood) to determine the best way to fabricate it— and to have the confidence that anything can be realized.
