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We take holidays seriously here at Fast Radius. We’re also committed to our mission to make new things possible.
This December we embarked on a mission to bring our festive spirit and additive manufacturing expertise together to create our take on a holiday classic: the nutcracker. Our final product is truly unmakeable with any traditional manufacturing method. Plus, it can actually crack a walnut. Here’s how we did it.
Design
The design process started by evaluating several different methods for cracking a nut.
Ultimately, we settled on a rack and pinion mechanism, which translates the rotational motion of a pinion (gears) into the linear motion of a rack (the rod that crushes the nut).
This design presented our engineers with the opportunity to show off their expertise in designing for additive manufacturing; we would make this nutcracker as one single 3D printed piece instead of the 12+ pieces it would take to make it traditionally.
Design engineering
Once we settled on a design that could consolidate all the parts of the nutcracker–including gears, crank, rack, handle–into a single piece, we needed to make sure the nutcracker would produce the force necessary to crack the walnut shell.
We consulted the scholarly literature on the topic (it exists, really!) and did some back-of-the-napkin math to determine the gear size, gear ratio, and crank design we’d need to create the right amount of force.
We also needed to ensure that the gears would function once printed. The design had to balance rotational clearances for powder removal while making sure the teeth of the gears still meshed effectively. To do this, we made sure every mating surface had a minimum gap of 0.5 mm.
While we originally contemplated using a combination of metal and plastic 3D printed parts, we made the decision to print the nutcracker entirely on the HP Jet Fusion 580 Color 3D Printer. This equipment is relatively new to the Fast Radius factory, and we wanted to put it to the test. We knew the material used in the 580, HP 3D High Reusability CB PA12, could make durable parts that were stiff and strong enough to crack a nut because it has nearly identical mechanical properties to the PA 12 we’ve used to print millions of parts on our HP 3D Jet Fusion 4200 printers. The 580 printer itself, however, varies slightly from the 4200, so we adjusted the design and orientation to the 580’s build volume.
The final product
Our careful design and engineering paid off. The nutcracker came off the printer fully functional and ready to use.
To give the nutcracker some extra panache, our Chief Designer took inspiration from carriage clocks and created two transparent pieces that would fit over the rack and pinion. We made these pieces from Whip Mix on Carbon® Digital Light Synthesis™. In the end, we opted to include only the smaller dome to make it easier to photograph the machine in action.
…And that’s the story of the Fast Radius nutcracker. Check out the video below to see it in action! We may have just started a new holiday tradition.