Oh, you fancy!
If you’ve ever ridden around on a Super73® E-bike, you’ve probably experienced celebrity status: getting stopped at every corner, strangers complimenting your ride, asking questions, and even wanting to ride it. No autographs please. This bike has become iconic and developed a well-deserved cult-like following. Devotees around the world have built fan pages and host meetups with hundreds of people flying through the streets of LA to Shanghai on these almost silent electric bikes. In addition to meetups, they hold competitions — for those more mechanically inclined — where riders customize every aspect of their bike, and judges vote on whose design is the most unique. We’ve seen everything — from custom rims and paneling to lowered bars to make the bike look even more like a classic cafe racer. Beyond competition, there’s a huge market for custom accessories so others can make these modifications. With this in mind, we decided to make our own accessories using 3D printing, because — well — that sounded pretty awesome.
What Do You Mean its 3D Printed!
When we started this project we knew we wanted to produce a portfolio of high quality parts that looked direct from the factory. What we didn’t consider was that no one (and we mean, no one!) would believe that the parts we produced were 1) made out of polypropylene filament and 2) printed on a basic desktop 3D printer, with no post-processing. In other words, no sanding or painting was needed to get it end-use ready. Apparently, most 3D printing enthusiasts wouldn’t dare attempt such a feat. But we like to live on the edge, and frankly, it made a lot of sense, especially with Braskem’s new glass-fiber reinforced polypropylene filament at our side.
Surface finish: Silky Smooth
Fused Deposition Modeling (FDM) 3D printing isn’t exactly known for surface finish. Parts from these machines typically have very visible layers, subtle artifacts on the surface, and very rough areas where support material once was. The only way to achieve a proper surface finish, for use on something like a bike for example, would be countless hours of sanding, Bondo (an automotive body filler, often used for car and household repairs), and paint. But, Braskem's new line of polypropylene flips this idea on its head. The glass fiber in the material creates a beautiful matte surface finish with a really unique, consistent texture that makes the layers disappear. And, because it’s so easy to print, we didn’t have any artifacts caused by warping or layers pulling apart. The main challenge with the surface finish was disbelief! When we brought the bike to the Rapid+TCT additive trade show in Detroit, many industry leading 3D printing experts couldn’t believe that the parts were 3D printed, let alone on an economically priced desktop FDM machine.
Mechanical Properties: Ready for Impact
We weren’t designing parts for just any electric bike. We were designing parts for an off-road, dual suspension, fat-tire beast. This bike is meant to be thrashed through the trails, then ridden on busy city streets for the commute back home, dodging onlookers and admirers. Because of this, we needed a material that would not only be lightweight, but durable enough to take a beating. We found this perfect balance with glass fiber-reinforced polypropylene. Polypropylene is a low-density material, making it extremely lightweight compared to other plastic. But it's very ductile or pliable, enabling it to survive an impact, or even be used as a living hinge. Reinforced with glass fiber, it increases its tensile strength but remains more durable than other alternatives available on the market.
Printability: As Easy as 1,2,3
A huge factor when using open source desktop FDM printers is finding materials that don’t take ages to dial in or get them just right, especially with very unique conditions. For example, nylon must be kept extremely dry before and during printing — in an enclosed environment to prevent warping — and printed at very hot temperatures, making it a challenging material to work with on most desktop machines. Polypropylene, on the other hand, while notoriously challenging to print with, can now be printed as easily as PLA with Braskem's new formulas designed for 3D printing. With a nozzle temperature of 240॰C, a bed temperature of 40॰C and BuildTak glue for PP filament, we were able to print flawless parts as easily on a $200 entry-level printer up to a large format industrial printer. And the mind-blowing piece? The parts printed from the different machines were indistinguishable! And, because polypropylene is naturally non-hydrophobic, it doesn’t need to be kept dry, like nylon for example.
Post-processing: Sheen and Clean
While not always required, post processing can make or break a project if too much is needed. Post processing for FDM parts is typically done to hide the layers and to clean up where the support material once was. I wanted to address this separately because not only couldn’t I believe how easily the support material came off for these complex parts, but how easy it was to clean these areas up. All it took was a quick pass over with a torch, and the rough patches speckled with white instantly blended into the surrounding finish. I’m not sure there’s a 3D printing material or process that cleans up faster than this for an end use part. Even Selective Laser Sintering (SLS) requires extensive depowdering and dying to achieve a finished look.
Not only were we thrilled with the outcome of the project, but the actual journey of printing the parts and cleanup was a breeze. We hope our experiment encourages others to see what's now possible with polypropylene materials. We can’t wait to see what you come up with!