Capitol Idea

It took more than 12 years to build the cast iron U.S. Capitol dome and rotunda. It took some 1,000 hours of electronic data processing, three years of planning and labor, some 55 gallons of polyurethane, and over than 280 casted parts to complete the exhaustively detailed, 12-ft.-high replica of the U.S. Capitol dome and rotunda, which is now part of the monument’s visitor’s center.

Midwest Model Making (www.midwestmodel.com; Indianapolis, IN) headed the project, beginning with amassing the 3D data and completing the final design integration and construction. It partnered with nearby Metro Rapid Protyping (www.metrorp.com; Nobelsville, IN), which translated Midwest’s 3D data of the iconic D.C. landmark to make the molds and cast the plastic resin for both the exterior and interior of the 500-lb. model. Divided exactly in half by a 12-ft. tall marble wall, the model depicts the dome from the tip of the Statue of Freedom to the foundation. On the opposite side is a cutaway of the rotunda in all its miniature grandeur, including ornate the friezes, paintings, sculptures, and the awe-inspiring Constantino Brumidi fresco, The Apotheosis of Washington, looming above it all.

Ed Watson, president and founder of Midwest Model, said there was no one single scanning or data solution to replicate the Capitol in 3D. The firm cobbled together external and interior designs from a variety of sources, including the first architectural drawings from original dome architect Thomas U. Walter, digital images shot by the design team, and a government-generated point cloud retrieved from a laser image scan of the Capitol, which was part of a larger post-9/11 effort to preserve U.S. landmark designs in case of a future terrorist attack.

“It was a laborious process, it very painstaking,” Watson said. “We put it together it chunk-by-chunk. The model represented 18 segments. We had to get the pieces small enough to fit into the stereolithography machines.” Each interior and exterior segment was repeated every 12 degrees to round out half a circle on either side, creating a symmetrical geometry inside and out.

Chris Young, stereolithography manager at Metro Rapid Prototyping, said the five-month mold making and casting process involved five SLA machines from 3D Systems (www.3dsystems.com; Rock Hill, SC)  churning out the masters nearly continuously, with smaller parts taking up to a day and some intricate pieces requiring a week to construct in meticulous layers. From there, workers created up to 20 castings per silicone tool. The solid color polyurethane supplied by Innovative Polymers (www.innovative-polymers.com; Saint Johns, MI) for the exterior did not require paint or additional coatings. 

Despite the careful attention to detail, the castings didn’t always fit like a glove. “We were hoping when we did the electronic files they all lined up flawlessly, but when we went from SL master and cast those they were all different, so we really had to cast twice as many as we needed and make custom cuts,” Watson said.

The exterior of the building is open for the public to view, photograph and even touch. The interior rotunda, however, is sealed behind a _-inch thick sheet of glass. Midwest built many of the sculptures and the picture frames with its own rapid prototyping machine. The archival artwork, provided by the Capitol architect, was printed on vinyl with four-color printing and artists hand painted the plastic casts.

Final assembly of the model involved integration of dissimilar materials, from plastics and acrylics to glass, metal, stone, concrete, wood and steel.  “Everything in there is touching and expanding at a different rate and it took several different disciplines to make it all work,” Watson said. 

 “As far as importance, it’s pretty hard to beat this project,” Watson said. “It’s going to be there long past my lifetime.”