Auger-Based 3D Printer Extruder
Hi Marcin, good to hear from you! I'm very excited about the progress I've been making recently. My approach actually skips the filament-making step entirely. Basically all I did was take the Precious Plastic extruder design and redesigned it to be vertical, a little lighter-weight, and switched out the motor for a stepper so that it could be easily controlled with existing 3D printer software.
Here's a basic schematic: Extruder Tutorial w: scenes.jpg
So it's a flake-extruding head, similar to a pellet-extruding head, and there is just an auger inside the hopper that pushes the flakes down into the melt zone and out the nozzle, while the gantry moves it around. The software thinks it's feeding filament, but instead it just moves the auger and creates forward pressure in the melt zone. It's a little goopy, but it works! The parts it's been making are wonderfully light and strong.
I've found that using a 4:1 NEMA 23 stepper is sufficient to get good enough extrusion consistency to print. Currently we're using #5 polypropylene test tubes that we get for free from a local company that produces them as a waste product. We shred them with a Precious Plastic shredder and then just feed the flakes right into the printer! Build area is 16" x 30" x 5", but could be easily expanded.
IMG_9151.JPG Print Time: 1hr 15min IMG_9159.JPG
The gantry I'm using is the open-source MPCNC (Mostly-Printable CNC), and the software I'm using is Repetier-Host with Slic3r. But really any CNC router gantry with a few inches of Z should be workable. The print head is about the same weight and size as a mid-size router.
Next steps/challenges are: -build a second hot swappable head for printing with HDPE, -automate the material feed with a cyclone filter/vacuum line -build a Z table that lowers on threaded rods to get more than 5" of Z. (shooting for 20-24" Z) -Potentially building a longer (10'x2'x6") one specifically for making trusses for tiny homes.
I've attached the full SKP so you can take a look. I would be very excited to work with you/OSE to do an independent replication of this project, either in person at the Farm or remotely over skype. Now that I know that it works, I really need to build better documentation for it, and the best way to do that is often to just build another one from scratch. All of the parts, including the MPCNC come in at around $500-600. The head itself only costs about $100-$150 to build.
Here's a short video I made that has a few more details.