PET-Filament from bottles

This How-To will explain how to turn PET-bottles into 3D printing filament using a filament extruder. Materials and tools needed: - Clean and dry PET bottles - Filament extruder and bottle cutter (after some research, we chose the PETALOT from function 3D, as it is open-source and of high quality, you can find the PETALOT here: https://github.com/function3d/petalot) - Stove or similar heat source - Safety goggles and gloves - Cutter knife, scissors and a wire cutter - optional: oven, wire crimper, soldering iron

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6 steps

1 Preparing the bottles

Collect and clean the bottles. Wash the bottles multiple times, remove labels and any sticky residue as much as possible. If the bottles aren’t completely straight (most bottles have embossings), the filament will be uneven in the end. Use a stove to straighten them. Fill a bottle with a bottle cap of water (around 5 milliliters) and close it up. Use the stove to carefully heat up the bottle, so the plastic can be deformed as the water evaporates. Wear safety glasses as the internal pressure build-up can cause the bottle to crack and gloves because of the heat. Once the bottle is straight, let it cool down before carefully removing the cap. You can then let the bottles dry completely.

2 Cutting the bottles

Using a cutter, carefully remove the bottom part of the bottle. Set the bottle cutter to the desired height. The recommended height can be found on the Function 3D FAQ: 0.2mm bottle thickness: 10mm strip thickness 0.25mm: 9mm 0.3mm: 8mm 0.35mm: 7mm Take the scissors and create a small strip before using the bottle cutter to create a long and even strip. Make sure it is as continuous as possible, as uneven strips can result in failed prints. Therefore, trim problematic areas with scissors.

3 Extrude the filament

Prepare the machine by rolling the PET strip onto the spool and inserting the strips into the extruder. The tip of the strip should be small, to make the extrusion easier. Secure the strip using the small bracket right before the nozzle. After that, push the strip through the nozzle and use your pliers to extrude 10-15 cm of filament. You can now attach the filament to the second spool and start the motor.

4 Prepare the filament for storage (optional)

Right now, the filament is difficult to store, as it is straight and won't stay on a spool. You can use an oven to make the filament rounder. Using a piece of metal wire, the filament can be wound into a spool and put into the oven at 120°C for about 10 minutes. After that, take out the spool and remove the wire. The filament should stay in place now. Warning: don't use this oven for food, as fumes might have developed.

5 Combining two pieces of filament

This is the hardest step of the process. I have tried many different methods and had only a few successful results. The following method worked best for me: melt the two end of the filament using a soldering iron. For optimal rigidity, melt them diagonally. Press the two ends together and use a wire crimper to join them. Use a cutter to remove excess plastic and you will have a pretty strong joint. Verify the diameter of the filament by passing it through a tube (1,75mm inner diameter). If you don´t have a tube in your 3D-Print equipment you can print a simple one or use this file to also clean your filament in the same step: https://www.printables.com/de/model/58302-175-filament-cleaner/files If your filament is too thick at the joint, the print will fail. Alternatively, you can also use a professional filament splicer.

6 Printing

Your filament is ready, but your printer might be not. The filament is hollow and too thin for some printers. I use a Prusa mk4, and I had to change the filament clip. I used this modified version of the clip from Terpuh Labs: https://www.printables.com/model/596608-mk4-modified-idler-lever/files The clip is normally used for TPU filament, but it works perfectly for thin filament as well. Once your printer is ready, test out different printer settings. For me, a temperature of 258°C works best, but it might be different for you. I also increased the flow factor to 150%, as the filament is hollow. Happy printing!

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