FDM (Fused Deposition Modeling) 3D printers use plastic. The resulting waste is less than a drop in the global bucket and pales in comparison to traditional manufacturing methods, but many hobbyists are eager to reduce their contribution to the plastic waste problem. Luckily, FDM 3D printers use filament made from thermoplastic that can be reused (and household waste plastic) for new print jobs. To make this process affordable, Thomas (aka Tinfoil Hat) designed this DIY extruder.
Resin 3D printers, including mask stereolithography (MSLA) models popular in the consumer market, use photopolymer resins that undergo a chemical change (photopolymerization) when exposed to UV light. There is no way to reverse this chemical reaction, so materials from parts printed with MSLA cannot be reused.
But FDM printers are different in that they use a thermoplastic filament. When exposed to heat, the filament melts. When it cools, it hardens. Because no chemical reactions occur, the process is repeatable, and that's exactly what makes Tin Foil Hat's DIY extruder work.
The first step is to shred suitable thermoplastic waste in a separate machine. This waste comes from failed prints, parts that are no longer useful, or trash. The waste must be clean and of the same type. Some thermoplastics are not suitable for 3D printing, but there is information available online about all the materials you may encounter. The shredded plastic is fed from the hopper into an auger and forced into the hot end of the 3D printer. The extruded plastic is pulled through the nozzle and reeled up for use in the 3D printer.
The machine is very similar to a 3D printer, but instead of a traditional direct drive or Bowden extruder, it only has an “E” axis and a hopper/auger. It requires a motor with a speed controller to drive the auger and two sets of temperature control components, the latter consisting of a PID temperature controller, a thermocouple, and a solid-state relay. Together, these control the heaters that melt the thermoplastic as it enters the hot end, maintaining the right temperature to ensure consistent extrusion without scorching.
All of these components, along with the power source and mechanical parts, are mounted on a frame made from welded steel tubing. As Tin Foil Hat points out, welding may sound intimidating to the uninitiated, but the basics of MIG welding are easy to master.
This machine allows you to utilize thermoplastics that would otherwise end up in a landfill, but be aware that the filament produced by this machine is inconsistent in both shape and composition, and while it will still work, it will not be of the same quality as new filament produced in a factory.