We got the MPCNC moving AND pushing plastic last night, a milestone I've been working towards for nearly a year! It would be generous to say that we successfully 3D printed anything last night, but this is a major step forwards towards that goal.
In Portland, every other Monday, there is a meetup called "Dorkbot" at CTRL+H, one of the local makerspaces. Dorkbot is a great place to get help on projects, as it's mostly very smart people who like solving problems. If you can bring smart people interesting and worthwhile problems to solve, they will often do very valuable work for free. (See also: "Sometimes the best way to get people to help you do something is to just start doing it wrong in front of them."
Nathaniel Garst, local 3D printing wizard, stayed troubleshooting with me (read: doing all the work) and at about 12:30am we got it pushing plastic and moving at the same time! The next step is to start dialing the temperature settings and speed, and see if we can build some large-format, low-resolution objects directly from recycled plastic flake.
This was the first time I have extruded polypropylene (#5), and it's exciting because this was plastic I had shredded up just a few hours earlier, with my precious plastic shredder. The flakes it's printing from were previously scraps of coroplast I had lying around from other projects, which makes it the first real piece of my house trash I've turned into something else! Not something useful yet, but you know, one step at a time.
There's still several lifetimes of troubleshooting ahead, but I feel pretty confident that the concept is sound, and of course, people are already doing this! It's not like it's my idea, it's just a good idea, and in my opinion kind of inevitable. My goal with this build is just to see if I can help make the tools required to do it a little bit more accessible. This whole setup, MPCNC and Extruder, should only cost $500 or less! If we can get it actually printing useful stuff, any kind of useful stuff at all (Wind turbines? Bike frames? Building trusses?) directly from plastic flakes, directly from the open-source shredder, that would be disruptively useful!