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3D printing filament recycling guide Answered

If you print a lot then you also have a lot of plastic to waste.
Support structures, brims, failed parts....
At some stage you start to wonder if it makes sense to invest into a filament extruder.

A filament extruder is a simple way to make you own filament.
A 25kg bag of granules in ABS cost only a few bucks and it will last like forever.
It also the prefered choice for a plastic extruder of any sort - fresh, new and clean material!

I do collect a lot of leftover plastic from my projects, is it worth getting a machine to recycle it?
Trust the advertisements of the commercially available models you buy one right away - if you can afford it...
But there is always a catch!

What are the basic requirements when collecting you already used filament?
It would be easier to state what you should avoid at all costs, so let me start with the most forgiving filament types - ABS and PLA....
Both will require that you keep your filament clean at all costs.
You want dust removed before the filament even enters you print head and same for all that you want to recycle.
Conatminents are the biggest deal breaker when you recycle filament!!!
That means parts of dissimilar materials,like when printing with two heads are just rubbish and go in the recycling bin outside.
The difference between ABS and PLS for recycling comes with the material properties.
ABS, if not printed too hot does not change too much, PLA on the other side usually ends up to be more brittle than new filament.
ABS should not be heated too high, same for PLA when you recycle.
But when PLA gets too hot it not only becomes really runny but also deteriotes very quickly.
Run a bit of PLA through print head like when changing filament or cleaning the head.
Do one run at normal temperatur, one run at 240°C and compare how the extruded and colled string reacts ;)
PLA is also prone to oxidisation and burning, espcially the black type is tricky here as you won't be able to see it, so avoid black if possible.
If it happens then you end up with rock hard piece, the size depends and can be tiny or bigger than a grain of sand.
A total nightmare if you did not spot that black spot in the filament and let the recycled stuff run through your printer.
A total block of the nozzle is the result.
Nylon I can't really recommend for recycling, too complext to handle it properly.
Same for filled filament like the wood or metal types.
With them it is really easy to accumulate a lump of filler that does the same block to your nozzle.

To wash or not to wash....
No matter what you try there will be always some contaminents that end in your collected material.
ABS can be washed with water and does not require too much fancy drying.
If in doubt you can even try your dishwasher or with a good bag your washing machine - both require proper rinsing several times and the last run with some added alcohol to demineralised or destilled water.
I use a box with a flyscreen cover and let it dry outside in the sun for a while.
PLA does not go too well with water especially with added soaps or detergents.
On the other hand it has no big problems tolerate things like Acetone.
Downside such solvents also dissolve a lot of contaminats which mean even though you can recycle your washing Acetone many, many time you always need fresh Acetone for the rinsing.
If you can try too keep all as clean as possible to eliminate the need for washing.

Can I get better results from my cheap filament maker or the one I build for some online instructions?
I find that there is always room to improve on things.
Before you even think about extruding your home made filament think about how to get your failed print into the thing ! ;)
The most vital part comes before you even heat the machine unless it is a really fancy one with a build in and big enough shredder.
That is right you need a shredder of sorts to be able to get your recycled material fine enough for the filament maker.
Some models you might quickly find as tutorials to build your own use basically a big wood drill for the mechanical part to simulate a meat grinder for plastic.
Even the better ones for real money often use this basic system in one way or another.
The problem is that you need to get all air out the material before it ends up to be the outgoing string you roll up.
Any bubbles in filament will certainly have consequences if the bubble appears during the printing of visible areas.
Imagine printing in vase mode and hitting a bubble during the last 20 minutes of a 3 hour print...
Unless it is dirt simple hobby built there will some mechanism to deal with the air.
However if what goes in is already very fine material it melts easier and air has it a lot easier to find a way out.
A good shredder will produce quite small granules but not strips or blocks.
The have their limits for intake size though.
The best way to get through bigger builds is a band saw, if have a clean table you can even recycle the "saw dust".
I prefer to heat bigger parts in the oven at moderate temps and then to use a hammer or press to flatten it first.

No shredder or no money to add one to the list? No problem!
If your filament maker does not have a pre-heated feeding area of sorts it makes sense to add one with aheating mantle and external temperature controller.
Trust me, if you have odd stuff to push in it is way easier if the material softens already before it enter the extruder drive part.
As the extruder will get quite warm anyway it can be as simple as adding a short pipe section with the heating mantle between the extruder inlet and feeding funnel or hopper.
the temperature in theis areas should of course be will below melting point and slightly above the temp when the material start to become plyable.
Hence the external temp controller here.
With this heating in the fedding area you really need to get your recycled material into a suitable size and shape to allow the material to be transported easy into the extruder.

Ok, I got it working, sort of...
You will need some time to find the prefect temperatures for per-heating, extruder temps and coooling, so take it!
If your filament comes out with bubbles or fine (hard and unwanted) particles it makes sense to cheat.
Most filament makers include a filter before the melted material enters the nozzle and really hot part.
In some cases this filter can be as simple as a steel mesh.
If none find ways to add one ;)
Said filter screen should be quite fine, preferably even finer that what you find in your faucet that airates thewater for the sink.
As a rule of thumb the mesh size should at least 15% finer than the nozzle size you intent to use.
Anything that makes it through will only be a problem for your nozzle if a lot of crap comes through and that you should be able to spot right away when the cooled filament comes out.
If despite this you still get too many bubbles check first if your temps are not going too high so the plastic start to boil in an area.
Too much speed can also cause a failure to expell all air in time, reducing the speed (watch the temps!!) can often resolve this nagging air problem.

It it really worth it then?
On a hobby level only if you print a lot and know you will keep going like this.
Otherwise you really need to be able to source or build your filament maker as cheap as possible.
Someone with a little print shop and three machines running 24/7 will certainly have a good benefit over time.
Especially if the recycling is part of the overall printing process.
Recycled material could be used in a dedicated head and extruder for supports, infills and so on.
For example in the printer dedicated to produce the biggest parts as these usually have bigger nozzle sizes anyway.
In a commercial sense however it must be considered what the material is worth in terms of normal recycling and the added hours and electricity cost for making your own filament.
Unless even the cheapest commercailly available filament still costs much more than what you need to invest to the machines and electricity over the time the man hours are the biggest killer.
If you need someone to monitor the filament maker and keep feeding it while making sure the spools wind up correctly then your own spools might end up quite costly.
So decide carefully before you invest or use you oven and a mold to make you own recyled plastic bricks for your garden beds and such.


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Isabella Smith
Isabella Smith

1 year ago

Nice guide! I did not know this was even possible!