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The Thunderhead filament extruder is an open source, small scale extruder designed by Techfortrade that can be used for recycling PET plastic bottle flake directly into 3D printing filament. A special emphasis throughout the design has been placed on using affordable and easily attainable materials. This repository serves as a host for the documentation and code used with the machine. We are using GrabCAD Workbench for the hardware development and will place links to the CAD files here on Github with each release. Current (though not necessarily stable) files can be accessed on our GrabCAD partner space.
To download a zip file with all of the v0.1 Solidworks CAD files including drawings, click HERE.
- Goals
- Use Case
- Current Capabilities
- PET Plastic
- Safety and Liability
- Building the Thunderhead
- Firmware
- Operation
- Contributing
- Maintainers
- Acknowledgements
- License
The Thunderhead is designed with the intent of making it possible to recycle plastic from the post consumer waste stream into 3D printing filament on a small scale with minimal start up capital required. This makes the following possible:
- Low cost 3D printing filament anywhere in the world
- Enable local capture of the value contained in waste plastic
- Access to expensive or hard to find items via 3D printing (eg. Open Flexure Microscope)
- Small scale business opportunities without need for large amounts of capital
- Enable local recycling where it is otherwise not possible
Techfortrade's work in Nairobi is an example of what can be done with the Thunderhead Filament Extruder. In 2018, Techfortrade 3D printed 50 digital microscopes that were distributed to 12 local schools. The microscopes were made using filament from extruder. The filament was 100% recycled from locally collected waste plastic.
Diameter: The Thunderhead does not yet extrude perfect filament meeting the standard diameter specifications for most 3D printers. The main issue is that the diameter fluctuates during extrusion. Typically the extruder will produce filament in the 1.8 to 1.6 mm diameter range. However, at times the diameter will move out of this zone to anywhere from 1.5 to 2 mm. Currently, we are using diameter sensors on our 3D printers to adjust for the filament inconsistencies on the fly. The results are very good.
Plastic Type: 100% post consumer PET bottle flake is the only plastic that has been tested with this extruder.
Production: Usually around 0.75 kg per hour.
Power Requirements: 240 or 120 volt versions of the extruder can be built.
The Thunderhead is designed to extrude Polyethylene Terephthalate (PET or PETE) for the following reasons:
- Prints very well on printers such as the Retr3D
- Easy to find nearly anywhere on the planet
- Has good physical properties
- Reasonably safe to work with, especially compared to post consumer ABS which often has Brominated Flame Retardants (BFR)
PET is easily identified by the following symbol usually located on the bottom on the bottle:
There are some challenges to working with PET plastic. A few these are described below. Follow the links to get more detailed information on these and other challenges:
- Crystalization - PET crystalizes when cooled slowly. To avoid making filament that is brittle like glass, a water bath is used.
- Low Viscosity - When PET melts it has a low viscosity and a low melt strength which makes it difficult to pull into a filament with an even diameter. The Thunderhead uses a cooling tube to help increase the viscosity and melt strength before the plastic leaves the extruder. The water bath also helps to
- Hygroscopicity - PET pulls water out of the air and holds on to it. This water can cause problems during extrusion and printing such as air bubbles, foaming and degredation of the plastic.
- Hydrolysis - The polymer chains in PET can break down in the presence of water at elevated temperatures. When this happens, the viscosity of the melt is reduced, making it difficult to extrude. To Avoid this problem, the plastic flakes must be thoroughly dried just before extrusion.
You are responsible for your own safety. This machine is under development. Please see the text in the license regarding Disclaimer of Warranties and Limitation of Liability.
Before you begin to build the Thunderhead, it would be a good idea to familiarize yourself with the machine and what is required for a successful build. The build documentation for the Thunderhead has been divided into several major components. Links are located in the side bar. Additionally there is a purchasing BOM that will help in gathering materials.
Note that you don't necessarily have to own all of these tools. A local shop could do some of the work for you. Especially the welding, lathe and milling work. Each component of the extruder has a "Building the Parts" page where tools needed to build each part are listed.
- Drill Press
- Metal Lathe - Threading the barrel and making the shaft for the gear box
- Welding (stick, oxy-acetalene or other) - For welding frames together
- 3D printer - Many of the complex parts in the machine are 3D printed
- Milling Machine (optional) - For milling flats into a few parts. Could be done with grinder and hand files though more time consuming.
- Horizontal band saw (optional) - For cutting stock metal to size. A hacksaw and vice will work, but will be slower.
Two firmware installations must be completed to get the Thunderhead up and running. These are:
- Thunderware.ino - For the Arduino Mega 2560 that controls the machine. It is located in the low voltage electronics enclosure.
- Drying_Hopper_Firmware.ino - Located HERE. Install on the Drying hopper's Arduino Nano.
The PET plastic must first be collected, cleaned and granulated. The plastic flakes must be dried at 170 °C for four hours before extrusion. Details for extruderthe extruder can be found here.
We'd love your help! You can contribute in many ways. Here are a few:
- Technical support on designs, code etc.
- Help improve the wiki and other documentation.
- Testing. Different Extrusion parameters, code, etc.
- Connect us with other interested individuals and groups.
- Donate! Techfortrade is a non profit organization working to create business opportunities in low resource settings.
Matthew Rogge is currently the maintainer of this repository.
The following people and organizations provided valuable help and guidance over the course of the project:
Matt Clark who provided hundreds of free man hours to assist with the re-design process.
Michael Uttmark who worked as an intern for Techfortrade. He did a huge amount of work on the code, electronics and documentation.
Frank Schoofs who volunteered his material science expertise to assist with thermal modeling required to design heating and cooling sections of the extruder.
Vasileios Grammatikakis an electronics expert who has assisted with improvements to the Thunderhead electronics.
Unilever plc. whose PET specialists have provided insights into working with PET, drying, and testing.
