From online to on the table: CU to put 'printable machines' on the Web

On the left, a ratchet mechanism with spring-loaded stoppers from Cornell's collection of Reuleaux teaching machines. On the right, a fully working replica, springs and all, created in plastic by a 3-D printer. Schools and museums anywhere in the world will be able to produce copies of this and other machines using stereolithographic files that will be posted on the Web by Cornell University Library. Photos courtesy of the Cornell Reuleaux Collection

By Bill Steele

Many of Cornell's collection of 266 19th-century mechanical teaching models, designed by the German engineering professor Franz Reuleaux to teach the underlying mathematical principles by which machines work, are visible on the Internet to students and teachers. Through collaborative efforts of the Cornell University Library and Cornell engineering and mathematics faculty, visitors to Cornell's Kinematic Models for Design Digital Library (KMODDL) can see photographs of the machines, watch movies of them in action and play with computer simulations of their movement.

But wouldn't it be better to have the actual machine in the classroom? That soon will be possible when Cornell puts a library of "stereolithographic" files online from which special printers can construct full-size, three-dimensional, fully working plastic models of the Reuleaux machines and similar machines in a collection at the Museum of Science in Boston. The 18-month project, funded by a $499,710 grant to Cornell Library from the federal Institute of Museum and Library Services, will make machines in the collections available to other universities and museums around the world.

In stereolithography, a computer starts with a three-dimensional image and slices it into many thin horizontal layers. A printer then reconstructs those layers one on top of another out of quick-hardening plastic. One printer uses a tiny jet that extrudes the plastic as it moves across a surface. Another consists of a platform immersed in a vat of liquid polymer resin on which a laser draws an image of each layer as the platform moves down. A typical 3-D printer costs about $30,000. Many large universities have them, and museums are starting to acquire them.

The process is widely used to make prototypes of manufactured products from computer-aided design (CAD) files. It has recently been used by paleontologists to share bone samples. "As far as I know, we're the first to allow the sharing of machines that actually function," said Hod Lipson, Cornell assistant professor of mechanical and aerospace engineering and computing and information science, a co-principal investigator on the project. Cornell workers have used 3-D printing to reproduce several preassembled, fully functional mechanisms, including ratchets, pumps and clock escapements, complete with links, joints, gears, worms, nuts, bolts and springs.

Stereolithographic files already are available on the Cornell Web site for a half-dozen complete machines, and the new funding will provide for the creation of about 30 more, according to John Saylor, director of Cornell's Engineering Library and principal investigator for the grant.

The files are modified CAD files made from 3-D scans of the actual physical objects. To make a machine with moving parts, the file must be modified by a human engineer. Free-standing parts must have supports added, just as in casting. Moving parts that rub against one another would fuse during printing, so the design must be modified to create slightly larger gaps.

In addition to sharing the machines, the grant provides for research to determine how to use them in education. Working with middle school teachers, the researchers plan to explore the ways machines can be used in the classroom and compare the use of digital representations of machines with use of the actual physical machines. They also will try to find the best ways to use original artifacts, digital representations and printable machines within a library environment.

Cornell's KMODDL Web site is an online multimedia representation of the machines along with digitized books and other information on the history and theory of machines. The site is part of the National Science Digital Library, funded by the National Science Foundation.

The models in Cornell's collection range from simple examples of basic gearing mechanisms to detailed reproductions of watch movements. The collection has been designated a "Heritage Collection" by the American Society of Mechnical Engineeers.

The Boston Museum of Science owns a collection of 120 similar machines built by American engineer William M. Clark in the early 1900s. Cornell Library staff will photograph the Clark models in Boston and produce stills and video sequences that will be added to the KMODDL site and used in the museum in conjunction with their display of the actual machines. KMODDL's developers see the Clark models as the first of many mechanical artifact collections that will be added to this resource.

Francis Moon, the J.C. Ford Professor of Mechanical and Aerospace Engineering, will add descriptions of the Clark mechanisms. His historical and theoretical descriptions of the models in the Reuleaux collection are part of the core content of the existing KMODDL database.

Lipson hopes the idea of printable machines will spread. "The availability of a centralized repository for printable models will provide an incentive for others to create and share physical educational models in other fields, bringing back some of the advantages of 'hands-on' experiential learning that has been lost to simulations and movies in recent years," he said.