On DIY injection molding and living in the future

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There are few things more beautiful to me than machined aluminum. So, I was delighted when my friend Brett Shellhammer invited me across the Hub courtyard last week to check out the plastic injection mold he had milled and test driven at TechShop in Detroit. For the uninitiated, injection molding is how the enclosures are created for lots of your plastic consumer goods. You put these two mold halves together like a sandwich and use a big press to force molten plastic through that port in the piece on the left. When you crack the mold open, you have a hard plastic shell the shape of the mold cavity.

“So what?” you might say. Your iPhone case, laptop case, and coffee maker are all made this way. Very familiar, right? Well, the thing is that five years ago this process/skillset/toolset was invisible magic and we only ever had access to the output. The maker movement has facilitated a tectonic shift in that dynamic.

Serial entrepreneur and outwardly a business guy, Brett is also a hardcore maker, fueled by a large desire to GSD (get shit done). So when his latest endeavour, The Quiet Coach, needed a plastic enclosure for part of their product and 3D printing was falling short, Brett flexed his maker-fu. It’s not a trivial workflow. He needed to 3D-model this enclosure in software. Then he took that virtual model and create an optimized toolpath for the CNC mill. He trained on the mill at TechShop, and then actually ran his toolpath against some aluminum stock to carve out the shape. More training, this time on the injection mold press at TechShop, was necessary. Finally, he had a complete toolchain with which to experiment, molding shells from different plastics. More importantly, he is now equipped to apply his learning to future challenges, not only in enclosure fabrication, but in any hurdle that requires modeling, machining, or CNC technology to surmount.

This is a small example of the watershed in manufacturing. It doesn’t supplant offshore manufacturing for large volume production, but rather complements it. Smaller volumes and quick-turn design changes (we used to say “rapid prototyping”) are within the grasp of mere mortal makers.

Click through for a few pics of the output and more machining porn…

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These are a few of the very first test drives of the new mold. Yes, they’re not perfect. It turns out that to get plastic to flow reliably to the corners requires the mold to be modified with vents. That’s a fairly easy tweak.

The finish on these shells is much better than you would see with 3D printing, where the rough finish of successive layers of plastic deposition is par for course. Brett decided the shell walls should be slightly thicker. That too is a straight forward tweak requiring only a slight change to the 3D model and toolpath followed by more milling of the existing mold.

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These stainless steel pins align the halves of the mold. I just love the striations a ball mill creates when removing aluminum. Magic!

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Here’s the mold sandwiched together. This goes into the press and after a little pre-heating, a powerful piston forces molten plastic through that port on the top side of the mold.

I asked Brett if I could record this progress with a few photos because it’s so important to capture the meta story of what you’re doing. In other words, the story of how you made the things that make the thing. This is understandably difficult for startups who are so busy building their product that they don’t have time for this additional work. That’s where I can help out. I love the tech. I love to shoot the tech. I’ll ask you informed questions about your product. And the maker/product manager in me may offer some suggestions. It ain’t free, but it will provide valuable collateral when you want to tell your story to investors and connect with customers. Hit me on email for a chat.


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