Introduction: Stool Made From Recycled Plastic
There's a lot of left over plastic all around us. Packaging, broken things, failed 3D prints, etc. Since the whole recycling system is a little bit broken, let's try to recycle some of it ourselves into a beautiful stool.
To do that, we need the following things & tools:
- Leftover plastics (sorted)
- Legs for the stool
- A frying pan you don't want to use for frying anymore
- An oven you don't want to use for baking anymore
Our oven uses a custom temperature controller, similar to the Precious Plastic Compression Machine. This makes it easier to dial in a proper temperature, but if you're a little more careful when setting the temperature, you can go with a stock oven as well
We also need a bunch of smaller things like the following:
- Some screws for the legs
- Welding gloves & a screw driver
- A round piece of wood, roughly the size of the pan
- Screw clamps
- A drill
- A saw and a file
Step 1: Collecting Plastic
To recycle plastic, it's good to know a bit about the kind of material you're working with. Not all kinds of plastics are the same.
First off, it's important what kind of plastic you're dealing with. If you want to recycle failed 3D prints, you likely already know what you're working with (PLA, ABS, PETG, etc.). Collect the pieces separated by type and ideally also by color to have a bit more control about what you'll be creating later.
For other kinds of plastics, there should be some kind of marking telling you about the type. Usually, it's part of the recycling symbol, with a number in it and/or the name of the type of plastic, like HDPE/PE-HD or PP. Check out this poster of different numbers and matching types.
Step 2: About the Legs
We'll be making the seat out of recycled plastic, but the legs should be a little more stable. There are a few different options, like building a frame from wood or metal, or individual legs made of either these two materials.
For this particular stool, I chose hairpin legs made out of steel. These can be easily fabricated yourself (ideally also from recycled materials), or bought pre-made. I found a set of four legs on eBay, of which I'll only be using 3. There are also a lot of sellers on etsy or similar stores selling these kinds of legs.
Main thing about the legs is their height. An average stool is about 45cm high. I'm aiming for a 2cm thick seat plate, so ideally the legs would be 43cm high. These fit the bill quite ok, just a few mm short.
Of course you can also go for a different height, and make a small table, nightstand, kids stool or anything else. Legs are available in all sorts of lengths so your inspiration is the only limit.
Step 3: The Pan
The pan you're using will dictate the shape of your seat. This one is 27cm wide on the top, on the bottom it's more like 20cm. This will make a bit of a small stool, but is still fine. You can totally go bigger though, as long as it still fits in the oven. You can even go with something like a square pan for a more interesting shape. Or a pan with an interesting bottom like a grilling pan.
This pan's coating started chipping so we sanded it off completely (make sure to wear proper PPE when doing so). If the coating is still intact, you can absolutely leave it on.
Make sure the pan is fine for staying in the oven for an extended period of time, especially its handle.
To make our lives easier later, I added some markings to the side of the pan, so I have a better chance of getting the thickness of the seat right. I'm aiming for 2cm, so I made some markings around the pan at 2cm above the bottom of the pan.
Step 4: Filling Up the Pan
Start piling up your plastic leftovers into the pan. If they are too big, use a saw, scissors, or whatever else you have on hand to make it smaller. Be careful with powertools, they might heat up the plastic and clog up (happend on my bandsaw with the PLA here).
Put a bit of thought into the pattern you want in the seat. Like you can have colors all at random, or split the seat into different sections of different colors. Now is the time to place the plastic pieces accordingly.
Step 5: In the Oven
Heat up the oven to the appropriate temperature. For PLA, 170-180°C worked great in our oven, but this might vary wildly depending on the kind of oven and the type of plastic you're dealing with. When in doubt, start low and increase slowly, to not burn your plastic. If you're working with different kinds of plastics more often, it's helpful to start documenting the temperatures, as they are specific to your oven as well. A good reference for temperature is this sheet by the Precious Plastic Team: Melting Temperature, which includes the most standard plastic types. For 3D printing plastics, check out the datasheets by your filament supplier.
Step 6: Refilling the Pan
Over time, the plastic in your pan will melt down. Add more fresh plastic of the same time, until you've reached the desired thickness, by checking the markings in the pan you made earlier. Sometimes, it helps to squish the plastic to remove air bubbles (especially when working with 3D prints with little infill, and thus lots of trapped air) or to keep a clean shape with the plastic sticks to the sides of your pan.
Step 7: Pressing and Cooling
When coming out of the oven, your plastic seat might not cool evenly, and get some more dimples and holes. If you're not happy with that, just put it back into the oven for a little longer.
To avoid at least some of that, you can press the plastic down into the pan while it's cooling down. There are numerous ways to do that, but a somewhat simple way we've been using is to cut a piece of wood to the size of the pan (ideally it's sealed on the side where it touches the plastic) and then press it down using screw clamps. I also added a steel plate to make sure it stays straight, but if you have a good eye, that might not be necessary. For the screw clamps, make sure not to use ones with these little plastic protection feet, as they will melt.
You can also just place something heavy on the wooden piece or the steel plate.
Leave to cool for a few hours, or just over night.
Step 8: Demolding the Seat
Once the seat has fully cooled, you need to get it out of the pan. Depending on the type of plastic and the coating of your pan, it might just pop loose all by itself. If it doesn't, you may need to do some convincing, like using a hammer on the back of the pan, or a screw driver or spatula on the sides once the seat has popped on the sides but not fully on the bottom.
Take a moment to celebrate the beautiful pattern you've created. Nice work!
Step 9: Cleaning Up the Seat
Likely, your seat has some bits of plastic sticking off to the sides. Take a small saw (I've had good successes with a metal saw) and cut off those bits. Make sure to save the bits you saw off, they can be recycled again on your next seat (or other plastic recycling endeavor).
For further cleaning, grab a file and round off the edges. You may also go for some sandpaper.
One important thing to consider: Filing and sanding your plastic seat creates micro plastics, which is widely observed as a bad move (correctly so). Of course, it's not really avoidable for some clean edges, but you may want to think about how you deal with the butt side of the seat. Likely, you'll "sit it smooth and into shape" anyways, so there's no real need for sanding. You can also choose to use a heat gun or other tools to smoothen out some rougher edges without creating more tiny tiny plastic bits. Either way, make sure to vacuum up all those bits that are too small to recycle again, so they don't end up out in nature.
Step 10: Get Some Stats
Back to your successes. It's super interesting (at least for me) to try and keep track of the amount of plastic I have recycled so far. So grab a scale and toss your seat on there. This one was almost 1kg. Sweet!
Step 11: Attaching the Feet
Time to get back on our feet.
Line up your feet on the bottom (previous top) side of your seat. Maybe you want to eyeball it (works well with only 3 feet), or make some more exact measurements (probably a good idea when using more than 3 feet). Mark your holes, and predrill. The PLA used for this stool was quite hard, so you'd break off screws without predrilling. This may be different for softer plastics like HDPE, but predrilling rarely hurts. Try to not drill all the way through the seat though.
Lastly, use screws to attach the legs. Make sure they're properly fastened, but don't go too hard on them, they will break off surprisingly easy.
Step 12: Take a Seat and Celebrate
Now it's time to put the stool the right way up, and test it out.
Wiggle it around a bit before committing fully, and then enjoy what you've built. Make sure to take some pictures and share them here, and everywhere else.
Step 13: Appendix: Marking Your Plastics
Almost forgot something very important: To ensure your stool can be recycled again, you
have to mark it with the type of plastic it is. Ideally you would print the recycling triangle on there with the appropriate number and text, and there are special sets of branding irons to do exactly that at home.
But a much simpler way is to use some of these punching letters you would usually use on sheet metal and punch the type into the bottom of your pots. Like so.
Participated in the