All 50 US states have a state bird and a state flower, but only eight states have an official state dinosaur. Colorado is one of them, which makes it pretty special, and the Stegosaurus that represents the state isn’t just the species in general but an actual Stegosaurus specimen that was found in Cañon City, Colorado and now resides at the Denver Museum of Nature and Science. The 26-foot-long Stegosaurus skeleton faces off against an Allosaurus in its museum exhibit, and has been aboveground since 1936, when it was discovered by a class of high school students, who worked with paleontologists to excavate it. The skeleton was nearly complete, a rarity for dinosaur skeletons, and this greatly interested Mike Triebold of Triebold Paleontology, Inc. (TPI).
TPI mounts and restores fossil skeletons and provides casts of them to museums around the world, and its headquarters are home to a collection of casts and original specimens which are on exhibit at the company’s hands-on natural history museum, the Rocky Mountain Dinosaur Resource Center. Triebold was looking to add a Stegosaurus to TPI’s collection – particularly the Stegosaurus at the Denver Museum of Nature and Science, which is known as the Kessler Stegosaurus after Frederick Carl Kessler, the teacher of the class of students that discovered it.
Traditional casting wouldn’t work in this case. The Stegosaurus is more than 26 feet long and over nine feet tall, which would still make for a doable cast if the specimen could be taken apart, but that wasn’t possible. The dinosaur was mounted as a permanent installation in the 1990s, with steel shaped around it, welded in place, and permanently puttied to the bones, making it impossible to ever take apart. Thus, 3D scanning entered the equation.
“We needed to three-dimensionally digitize the skeleton that could not be dismantled so that a replica could be 3D printed,” said Matt Christopher of TPI. “The dimensions and surface details needed to be close enough to what we would get from a silicone mold so that we could hand-finish 3D prints to look exactly like the original specimen.”
To scan the dinosaur, TPI used an Artec Spider structured light 3D scanner along with Artec’s Studio 3D scanning and processing software. The 3D scanner was provided by Artec’s local partner 3D Printing Colorado.
“Our Artec Spider captured exactly what we needed,” said Christopher.
The Spider was used to 3D scan individual bones and regions of the skeleton as individual projects in Artec Studio.
“This involved crawling inside the rib cage (yes, a full-grown person fits inside the rib cage of Stegosaurus) to capture the dorsal vertebrae forming the dinosaur’s back and the medial surfaces of the rib cage, shoulder blades, and hips,” said Christopher. “There were also some interesting poses taken atop a step ladder to reach the tops of the big fan-shaped plates on the dinosaur’s back. We were able to capture all of the elements we needed, from the tip of the nose to the huge spikes at the end of the tail.”
In the end, they had 629 individual scans across 71 scan projects. In order to save time, they decided to skip scanning parts that could be mirror-imaged to generate the other side, like legs and ribs. The scans then needed to be aligned, cropped and converted to 3D mesh files in Artec Studio.
“The alignment features in Artec Studio were absolutely paramount to the success of this project,” said Christopher. “Aligning each scan was as simple as manually orienting to a loose approximation of the correct position and letting the alignment tool refine the fit to perfection. Using Artec Studio to create and control the mesh generated from the aligned scans allowed us to extract the exact level of detail we wanted for manipulating and 3D printing.”
No artifacts presented a problem in the exported meshes, thanks to a filter in Artec Studio that removes all elements smaller than the master scan.
“Had we been scanning individual, unmounted bones, it would have been easy to generate complete, watertight meshes directly out of Artec Studio that would have required no additional post processing,” said Christopher. “With the steel armature remaining to be removed and the obstructed surfaces left to be reconstructed, watertight meshes were not really an option or a necessity for remaking the Stegosaurus.”
The meshes were then imported into ZBrush for separation of articulated elements, reconstruction of surfaces that were impossible to reach with the 3D scanner, like the spaces between articulated bones, and removal of the steel armature that obscured some bone surfaces.
3D printing the bones was a big job that was taken on by multiple 3D printers, ranging from a Formlabs Form 2 SLA 3D printer to a large Atlas from Titan Robotics. 3D printing took six months, and when the prints were finished they were lightly resurfaced by hand and prepared for molding by adding mockups for internal steel armature and articulating some specimens to be molded in sections rather than as individual bones. Each completed bone or assembly is called a master; these masters were then molded in silicone rubber. The molds were then fitted with internal steel to be surrounded by plastic resins in the casting process.
“The plastic is poured around the steel, so no external armature that would hide bone surfaces is needed,” said Triebold. “With the casts poured around the armature, we can assemble the skeleton in any one of an infinite number of poses and weld together the steel protruding from inside each plastic cast. The mounted skeleton is then ready for hand-painting and delivery.”
The completed Stegosaurus will be on permanent display at the Royal Gorge Dinosaur Experience.
“With our Artec Spider we were able to marry the best technologies of today with the most advanced traditional methods of molding and casting to create an exact copy of that great dinosaur without even touching it,” said Triebold. “Now, how about that Allosaurus…”
Discuss this and other 3D printing topics at 3DPrintBoard.com or share your thoughts below.[Images provided by Artec 3D]
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