Introduction: Turn PET Bottles Into 3D Printer Filament

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Fusion Projects »

A few week's ago I published a project on the controller that I designed for my PET bottle recycler. I've now completed the rest of the components and I’m going to use it to turn a few old PET bottles into filament for my 3D printers.

There are four main elements to the recycler. Starting from the bottle side, we’ve got a cutter which cuts the bottle into an even-width continuous strip. Then we’ve got the hot-end which the strip is pulled through to partially melt and convert it into the size and shape for filament. Then there is the reel which pulls the filament through the system and stores it for printing, and lastly is the controller on the front which controls the hot end temperature and the reeler motor.

The device doesn't fully melt the PET strip, it just softens it enough to be folded over into a cylindrical shape that is the same diameter as common 3D printer filament. 


Supplies


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Step 1: Designing & 3D Printing the Parts

I started out by 3D modelling the design in Fusion360. I designed all of the 3D printable components and modelled some of the main bought-out elements to get the general shape and design right.

Then came a lot of 3D printing. I printed the parts out in PETG for added strength and I had to make adjustments and redesign some of the parts until I was happy with them. 

You can download the CAD files from my blog if you'd like to make your own PET2Print machine.

The main components are assembled onto two lengths of 2020 vslot extrusion with a set of legs on either end. These legs and the other components are attached to the extrusions with vslot nuts and M5 button head screws.

Step 2: Assemble the Bottle Cutter

There are two main 3D printed parts for the bottle cutter, the base which holds the cutter and bottle support, and then the guide which just keeps the strip in the same orientation through the bearings and when it feeds into the hot end.

To join the two pieces, we need to add some M3 threaded brass inserts to the side of the base, which we’ll melt into place using a soldering iron.

The cutter uses two 608 ball bearings to cut the filament. These are really cheap and easy to get as they’re the same size bearings that are used for skateboard wheels and fidget spinners. To turn them into a cutter, we need to sharpen one face of each bearing. I did this on a bench grinder to make sure they’re kept square.

We then need to epoxy two M8 studs into the base to mount the bearings on.

We also need to add a metal strip underneath the bearings. This stops the bottle from quickly wearing out the printed base.

A small washer is used under the first bearing, with its flattened or ground face up so that it doesn’t rub on the base. A nut holds it in place. We then add a nut to the second stud, then the bearing with the ground face down, just at the right height to contact the face of the first. A nut holds the second bearing firm against the first bearing and the nut below it.

We can then screw the guide onto the front of the base with some M3 button head screws.

To finish it off, let’s also add a M8 rod for the PET bottle stand. This will hold the bottle upright to feed the end into the cutter. It is held in place with a nut and washer on each side. 

Step 3: Assembling the Hot End

The nozzle is a standard 0.4mm nozzle, so we need to first drill that out to the filament diameter. We're aiming for 1.75mm but the filament expands a little after it leaves the hotend, so we'll drill it out using a 1/16" drill bit, which is just under 1.6mm.

The back of the heat block has a small hole for the heat break, we're going to open this up with a tapered drill bit so that it is slightly larger than the strip width and the taper will help gently fold the edges over until we reach the nozzle diameter.

We can then mount the heat block onto the holder. I've used some M3x40mm button head screws through the heat block and then nuts to hold it onto the plywood plates on each side of the 3D printed holder. The plywood plates act as the heat break in this design and stop the screws from melting the plastic holder. 

Step 4: Assembling the Reeler

To make the reel, we need to melt some M2.5 threaded brass inserts into the main half of the reel for the opposite end to screw onto - this is split to make it easier to 3D print without supports.

We also need to add some inserts to the reel holder for the small catches that hold the reel in place while it is running.

Then we can screw these parts together with some M2.5 screws.

The 8mm shaft needs to be epoxied into the reel holder for the drive system to turn.

Next let’s press another two 608 size bearings into the reel stand, one on each side. We’ll use an 8mm shaft as a guide to keep them aligned.

Next, let’s mount the motor onto its holder using four M3 button head screws.

Then we can mount the base onto the top of the v-slot extrusion, and the motor holder onto the underside.

The reel is driven by the motor through a belt and pulley system on the back. So we can push the reel’s shaft through its base with a spacer between it and the bearing, then another spacer on the opposite side. We then add a pulley to finish it off and the grub screw holds it in place. A second pulley sits on the motor shaft, with a belt connecting the two.

The belt is tensioned using the relative movement between the reel base and the motor holder, pulling them further apart puts more tension on the belt. 

Step 5: Assembling the Controller

I designed a new PCB that swapped the UNO that I used in my previous controller out for a pro mini and brought the components a little closer together. 

I then soldered the components onto the PCB, starting with the smallest and working to the largest, with the Arduino going on last.

I also 3D printed a housing for the controller, but before we put it into the housing we need to program it and set up the stepper motor driver’s current limit - the code and more information on how to set up the controller are available on my blog.

Then we can install it in its enclosure. First, we need to add some M3 threaded brass inserts in the bottom to screw the PCB to. The PCB is then held in place with some nylon standoffs which double up as a means to hold the top cover in place.

We can glue the OLED display to the inside of the top cover with some hot glue and connect it to the PCB with a short ribbon cable.

Then we can then screw our element and thermistor into the terminals, plug in the stepper motor and then close it up with some M3 button head screws.

To finish it off, a knob gets pushed onto the rotary push button and we can mount it onto the base. 

Step 6: Turning a Bottle Into Filament

To prepare a bottle, we first need to remove the label and residue as well as any date markings. I found that acetone works well for this.

The cutter works best with a smooth surface and most bottles are rippled in some way. You can smooth them out over some heat with a drop or two of water inside the bottle to pressurise it slightly - Be very careful not to heat the bottle up too much and wear gloves when opening it up so that the hot steam does not burn you.

We can then use some needle nose pliers to feed it through the hot end, which will need to be preheated to about 220 degrees Celsius and then on to the reel. The reel has a small hole on one spoke which we can feed the end through to tie it off.

Finally, we can turn on the reeler motor to continue pulling the filament through. I found a speed of 22 works well for my bottles.

Then we just wait for it to turn the bottle into filament. You can also cut the bottle beforehand to reduce the load on the motor, you'll then just feed the strip through to the hot end. 

Step 7: Printing With the Filament

Once the bottle has been converted into filament, we can transfer it from the reel over to the 3D printer to try a print. I've started by printing a benchy and calibration cube so that you can see how they turn out.

There is a bit of adjusting to do on the first few prints as the filament is not quite a solid 1.75mm section, it is hollow in the middle. I found that increasing the flow rate to about 135% gets good results. I print with a bed temperature of 70 degrees and a hotend temperature of 260 degrees.

Once I had the settings right, I was actually pleasantly surprised by how well this filament prints. The calibration cube came out looking really good. The benchy showed a few signs of stringing and a little under-extrusion in places but is also really good for homemade filament. It's obviously not as consistent as factory-produced filament but it's usable for home projects.

Let me know in the comments section below what you think of the PET2Print recycler and any suggestions for improvements to it.

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