Shop Realizes Sculptor’s Concepts with GibbsCAM

Monday, Jun 4, 2012 5:00 AM

GibbsCAM's Hole Manager automatically recognizes holes by CAD-assigned
characteristics, marks each hole with a point and normal vector, which are
then used to program proper tool rotation for boring, drilling, tapping and
countersinking holes. This can facilitate programming that would be
nearly impossible for 5-axis machining and save hours of time,
as it did for programming the 1,100 holes of this sculpture.

Tom Shannon intended his sculpture to reflect several relationships to Fuller's architectural concepts, both physically and optically, two such concepts being geodesic geometry and harmony with the environment. Also, to perform as "an interactive optical instrument," Mr. Shannon required the internal and external surfaces to be mirrors, which would reflect the environment within and without. To create the relationship to geodesic polyhedrons, Mr. Shannon enlisted the geodesics expertise of scientific designer Joe Clinton, who developed a pattern of holes on a CAD system to achieve the effect.

Joe Clinton provided Blue Chip the design and "seed pattern" for the holes in a Cadkey file, which Mr. Denny transferred into SolidWorks to create a solid model, duplicate the hole pattern across the spherical surface, use mass properties to physically balance components, and provide machinable models for programming a 5-axis machine tool with GibbsCAM.

The upper sphere has to be machined as two hemispheres. The two pieces could not be brazed or epoxied together because access to the interior surface would be required for dusting or re-polishing. This created the most difficult part of the project, which was matching the two halves while maintaining continuity of the hole patterns. Once resolved, machining could begin.

As with all Shannon sculptures, the visible and highly reflective components begin as solid 2024 aluminum billet. Programming the general machining was easy, but, Mr. Denny said, "Programming the holes would have been a nightmare, had it not been for the combination of SolidWorks and GibbsCAM, which give us a lot of power."

GibbsCAM has a utility called Hole Manager, which simplifies and automates hole-making operations, which can often be achieved with three mouse clicks. Hole Manager automatically recognizes holes by characteristics assigned within SolidWorks, puts a point at the center of each hole, and provides a normal vector to the hole. The points and normal vectors are used by GibbsCAM to program the proper tool rotation to perform the specified hole operations – boring, drilling, tapping and countersinking. It is especially useful when holes to be made are on multiple planes, such as the infinite number of possibilities presented by spheres. "Programming 1,100 holes for 5-axis machining was still difficult, and I spent a lot of time doing it," said Mr. Denny, "but it wasn't the nightmare it would have been without SolidWorks and GibbsCAM."

After machining, polishing each hemisphere was extremely time-consuming, requiring several steps with progressively finer grit, to leave perfectly spherical reflective surfaces. As with procedures in using SolidWorks and GibbsCAM, Blue Chip has developed processes for polishing to pass Tom Shannon's scrutinizing eye. Even so, there's one task that has yet to be simplified and automated. After polishing each hemisphere, the shop spends five hours cleaning to remove polishing compound from all of the holes. "You just sit down with an electric drill and a million Q-tips, and get it done," Mr. Denny said.

The required detail and patience pay off with the engineering, programming and machining challenges that Mr. Denny enjoys from working with Tom Shannon, and the association of his work with worthwhile causes. Also, as often happens when one's work is admired, Blue Chip was rewarded with a new client, when Joe Clinton had the shop engineer, machine, polish and assemble his Radix Universum Triplets-egression," a mathematically-based sculpture of polished aluminum. On June 6, Mr. Denny will have the added satisfaction of seeing the Shannon-Clinton designed, Blue Chip made, OmniOculi sculpture in the hands of another contributor to humanitarian causes.