The Hangprinter project by Torbjørn Ludvigsen has developed a promising and affordable concept for a large scale cable-driven 3D-printer, that has the potential to serve as the framework for an entirely new class of 3D-printers, enabling distributed local manufacturing of large end use products like furniture, vehicles, buildings etc. Up until now the Hangprinter has relied on regular FDM-extruders leaving the project far behind its true potential. Being great for desktop printers, those extruders are not suitable for printers beyond the 1 cubic meter class. Filament extrusion hits the wall in terms of speed, cost and sustainability.

We decided to circumvent this obstacle by developing an affordable pellet extruder, that enables you to print not only with industry standard plastic pellets, but also and mainly with re-granulate plastic made from your plastic waste.

Design Drivers

• Throughput 1-2 kg/hr depending on polymer
• As light as possible
• Nozzle sizes up to 10 mm, easy to swap
• Sturdy base for attachment
• Enough heating power to cover as many polymers as possible
• Tolerance for potential foreign objects (dirt, sand, etc.) within the granulate
• Automatic material transport and dispensing
• High flow cooling for the print area

The compression screw

The compression screw is the key element of a pellet extruder. It differs from a regular auger bit by having a flute depth that decreases towards the tip. The compression screw is disected into three different zones: the feed zone, the compression zone and the metering zone. The screw adds shear to the plastic granulate and accelerates the melting process. These compression screws are difficult to manufacture, so we are going to cut corners and we will use the RobotDigg 16 mm extruder screw, barrel and nozzle for now.

The RobotDigg barrel has already a flange with standard Nema 23 attachment holes and it comes with an exchangeable nozzle.

• Compression ratio 2.5

Pre-requisites

Certain set of tools is needed to start your own project. Both software and hardware tools. We are designing the pellet extruder in Autodesk Fusion 360. Although not open source, you can obtain a personal, non-commercial, license for free from Autodesk. We will provide also exchange file formats if you prefer to use other CAD software.

Among other things you should be prepared to have access to following tools:

• Drill bench
• Soldering iron
• 3D-printer
• CNC-machine
• Handtools like allen keys, wrenches, screw drivers, metal saw etc.

A word of warning

The barrel is heated by powerful mica band heaters. This leads to two serious hazards.

1. The heaters are powered by grid voltage which poses a danger of a lethal electric shock! If you are not trained in connecting electric circuitry, please ask someone with experience.
2. The heater bands can generate heat up to 450 degree Celcius, which can lead to serious burn injuries or a fire hazard.

Please keep this always in mind. Ask always, if in doubt.

Roadmap

• 09/2019 - 11/2019 Design, component selection
• 11/2019 - 12/2019 Manufacturing, assembly
• 01/2020 - 06/2020 Extrusion testing, iteration
• 01/2021 - 02/2021 Print testing

Project on Github

https://github.com/Bloft-Design-Lab/Bad-Ass-Pellet-Extruder