Deltabot History The Mini Kossel is an open-source parametric “delta robot” 3D printer, first built in Seattle in 2012 by Johann C. Rocholl, the father of deltabot printers. In deltabots, linear motion is generated by three drive towers, so the print head can move equally fast in the x-, yand z-axis, with fewer moving parts. A Bowden extruder keeps the head light and balanced. (The deltabot design also bypasses the Stratasys patent on heated build chambers, which specifically calls out a Cartesian platform.) The OpenBeam Kossel family of printers is being developed at Metrix Create:Space in Seattle, led by Terence Tam, creator of OpenBeam aluminum extrusions. (OpenBeam just completed a successful Kickstarter for the Mini Kossel’s big brother, the OpenBeam Kossel Pro, which won an Editor’s Choice award at Maker Faire Bay Area in May 2013.)
Mini Kossel: Kit Only The OpenBeam Mini Kossel we tested was a prototype, just the second of its kind. It’s slated to be sold this fall as a mechanically complete kit, minus the 3D-printed parts, electronics, motors, build platform, and hot-end; these nonmechanical items will be available as configurable options. Depending on the electronics package chosen, the full deltabot kit will retail for $810–$899. The machine was sent to us preassembled (at our request) and without instructions (which are in progress), so we’re unable to rate the kit’s documentation or ease of assembly. General documentation and a complete bill of materials for the Mini Kossel are available on the RepRap wiki at reprap.org/wiki/Kossel.
Design Highlights The OpenBeam Kossel family is unique in the RepRap world as it maintains
100% part compatibility between Pro models (with injection-molded parts) and RepRap models (with 3D-printed parts). Both branches are open source. The OpenBeam Mini Kossel also features improvements such as an automatically deployed bed leveling probe that compensates for bed tilt and bed height calibration. By day, Tam is a mechanical design engineer for a microscope company, and it shows in the Mini Kossel’s construction. He used affordable copies of high-grade commercial linear recirculating ball rails, like those in fine optical instruments, to achieve smooth linear motion and rigidity.
Nice Prints, Unique Auto-Leveler Overall, we got very nice prints from the Mini Kossel. It printed the only MAKE robot with no “ringing” flaws (see page 59), and it also did quite well on the difficult Secret Heart Box model. The auto-leveling probe is fantastic; I thoroughly enjoyed watching it hop around the build platform before each print. We experienced retraction issues when using the provided slicing configurations, leading to tiny overextruded “warts” on some prints. After consulting Tam and Rocholl, we were able to increase the retraction settings and dramatically decrease this problem.
Printing Untethered We also experienced issues with the Vici LCD display and were unable to print untethered using onboard controls or SD card due to firmware incompatibilities. I asked Tam about it. “Debugging the SD card issue is one of our higher priorities,” he said. “We’re actually developing our own electronics, and it’s our intention to have SD card printing enabled on our electronics.”
Primo features
Auto-leveling probe and glass print bed Delta robot positioning system RepRap and Pro-grade interchangeable parts High-grade commercial linear recirculating ball rails
Who’s It For? Tinkerers
Pro Tips
Don’t touch the print head during auto-leveling. Doing so will cause an inaccurate reading and can cause the probe to tear the tape on the platform. Keep this printer cool. In a hot room, we found that a box fan improved PLA cooling and gave better prints. Check out Johann’s Mini Kossel Blog (deltabot. tumblr.com) and the Deltabot Google Group.
Looking for a radically different 3D printer and a new kit build? The Mini Kossel is for you. How'd it print?
Conclusion This is not a printer for beginners, but if you’re a tinkerer in search of something different and you’re looking for your next kit build, we highly recommend the Mini Kossel. We had a fantastic time with it, and I’m seriously considering building one myself.
1.1875"
Defeat the Cartesianists! Unique in our tests this year, the Mini Kossel’s “deltabot” design has three arms, each attached to an independent, stepperdriven vertical axis, which results in a simpler machine with a smaller footprint and faster positioning than other printers.
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