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Injection-molding the "Illuminati Pyramid"

An orange plastic illuminati pyramid rests on top of a dollar bill. The unfinished pyramid printed on the bill is visible
A child's drawing of an "illuminati pyramid." It is labeled "Aluminautie."

The Illuminati Pyramid

Every year, Northwestern reaches out to local elementary school students to dream up new and unusual ideas of toys to injection-mold.

Of the three drawings my team received, we selected the “Aluminautie” design. Over 12 weeks we designed models, programmed and milled molds, and produced a run of 100 parts.

My Role

On our team of four mechanical engineering students, I developed the early CAD models of our parts. I also was responsible for the CAM programming and CNC milling of one of our four mold blocks.

A 3d model of half of a pyramid, with notched cutouts
Several plastic pieces assembled into a partial pyramid. The internal tabs are shown interlocking

Making it all Fit Together

Pyramids, as it turns out, are a difficult shape to assemble. My team and I first tried splitting the pyramid in half and molding it in two identical shells that fit together like puzzle pieces. While the parts themselves met best-practice design guidelines for a thin-walled part with no undercuts, the molds couldn’t be manufactured with standard tooling.

We then revised our design: After briefly considering a flat, foldable pyramid with living hinges, we selected an assembly of 5 flat panels that snapped together with a series of open-ended tabs and pockets

The first design concept

The first revised design

A 3D model of one face of a pyramid, showing tabs on the interior face

The final parts, fit together

Several 3D printed pieces of toy pyramids rest on the bed of a 3D printer

Lessons Learned

  • 3D Printing: Using my own desktop 3D printer, I printed sample parts from the very beginning stage of the design process. These models were used at every stage of the process to communicate and iterate on our design.

  • Mold Design: CAD and 3D-printed models helped us visualize how tools could (or could not) physically cut molds for the parts in different orientations. Mold design quickly became a central concern for the team; this early emphasis paid off with molds that were easier to cut, modify, and use.

  • Kids: Since when do they know so much about the Illuminati?


Of the 17 injection molding design projects, the Illuminati Pyramid was awarded first place by a team of academic and professional experts in injection molding.

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