Symmetrical eyeglass frames made possible with cross-sectional scanning

If you wear glasses with plastic frames, those frames are probably not symmetrical. You may not know it, but there is most likely an imperfection, something that occurred during the design process, which makes one side of your glasses just a little different from the other side.

A tool designed to help conduct part inspections, conduct mold verifications, or do reverse engineering has been used by one manufacturer to mold almost perfectly symmetrical eyeglass frames, reducing tooling by as much as 50 percent. The person who did it was Steve Gaspardo, owner of Gaspardo & Assoc. (Batavia, IL). He used the CSS1000 made by Capture Geometry Inside or CGI (Eden Prairie, MN). "Using the CGI system allowed us to digitize one half of the frame and then create mirror-image data for the mating half."

First described in IMM early last year (see March 1997 IMM), the CGI CSS (Cross Sectional Scanning) system works like this: The part is first encased in a block of epoxy, which is mounted on an aluminum base on the ACSS mill table. A fly cutter then machines away thin layers of the epoxy-encased part in slices .0005 to .0100 inch thick. After each layer is shaved off, an optical scanner (200 to 1200 dpi) captures the exposed surface of the part and saves the data to a file. With each successive layer, it captures every corner, edge, slope, angle, and dimple in the part. This data can be rendered in a point cloud, scaled up, scaled down, imported into a 3-D CAD package, output as an STL file for prototyping, or exported as an NC tool path to build a mold. This is where the eyeglasses come in.

Gaspardo used the ACSS system to digitize one half of the frame, creating an electronic duplicate of the scanned half. He continued development by producing verification models from a rapid prototyping system for final design review and approval before tooling began. The data was then imported to an Imageware software program, which defined the mold parting line so the core and cavity could be created from the digitized point data.

The STL file used for the rapid prototype part was translated into CNC code, tool paths were generated using Delcam's Powermill, and the molds were machined. "We did this without having to create any CAD surfaces," Gaspardo says. "We can now bypass CAD file creation to further reduce product development time, which allows products to reach the marketplace faster than ever." Overall, the timeframe for tooling development and creation was shrunk from eight to 10 weeks down to four.