Vicious Little Desktop Shredder Pulverizes Plastic Waste

We’ve all likely seen video of the enormous industrial shredders that eat engine blocks for lunch and spit out a stream of fine metal chips. The raw power of these metal-munching monsters is truly fearsome, and they appear to be the inspiration for SHREDII, the miniature plastic shredder for at-home recycling of plastic waste.

The fact that SHREDII isn’t all that large doesn’t make it any less dangerous, at least to things smaller and softer than engine blocks, like say fingers. The core of the shredder is a hexagonal axle carrying multiple laser-cut, sheet steel blades. The rotating blades are spaced out along the axle so they nest between a bed of stationary blades; rotating the common axle produces the shearing and cutting action needed to shred plastic.

On version one of the shredder, each blade had two hooked teeth, and the whole cutting head was made from relatively thick steel. When driven by a NEMA 34 stepper — an admittedly odd choice but it’s what they could get quickly — through a 50:1 planetary gearbox, the shredder certainly did the business. The shreds were a little too chunky, though, so version two used thinner steel for the blades and gave the rotary blades more teeth. The difference was substantial — much finer shreds that were suitable for INJEKTO, their homebrew direct-feed injection molding machine.

There’s a lot to be said for closing the loop on plastics used in desktop manufacturing processes, and the team of SHREDII and INJEKTO stands to help the home gamer effectively reuse plastic waste. And while that’s all to the good, let’s face it — the oddly satisfying experience of watching a shredder like this chew through plastic like it isn’t even there is plenty of reason to build something like this.

Thanks for the tip, [Alen]!

20 thoughts on “Vicious Little Desktop Shredder Pulverizes Plastic Waste

  1. Neat…. Is it wide enough for secure media destruction also, like burned CDs and DVDs? Or does it need a few more layers of teeth?

    I am interested also in the PET bottle munching abilities to turn waste into feedstock too though. I feel I’d like to try a version with pedal power, maybe old excercise bike bottom end.

    1. That exercise bike would end up being damn hard work, or take quite some time gearing depending… Fun idea though, and its perhaps good motivation too, if it helps you get your exercise in and generate new plastic for your next thingambob.

  2. I feel I missed some slang development – when did ‘gamer’ start referring to folks messing about with 3D printing?

    How do we now refer to the dedicated players of interactive electronic entertainment?

  3. I had planned to make one of these, but was going to put an image on the side of The Shredder from Teenage Mutant Ninja Turtles shredding (playing a guitar), and have a cheezy guitar shredding riff play when switched on. It would announce itself upon being turned on as “The shredder!! in an 80’s hairmetal voice, as a voice over over the guitar solo, and the guitar solo of shredding would continue, triggered by load sensors, to play whenever “The Shredder!!” is actually shredding something.

    I like this idea still.

  4. So we use a huge amount of energy to transform sponge iron to iron, iron to steal, cut the iron in parts with a lase made of tons of complicated stuff, build and add some not so useful motor, bolts and other stuff to create a device that can handle some not so great plastic and transform it into some still not so great and with not really known consistence polymer material.

    I applaud the build. But to add some perspective: a not done failed print would easily outnumber all the efforts. Put the energy in better simulation, better print tools and save way more material+energy.

    Or scale up the process to handle more material. Collection infrastructure etc.

    Oh, looks like I missed the point. It is to create youtube revenues.

    1. There is a very valid point to such small scale recycling for some – you can only simulate so much, at some point you do have to test it in the real world and find you need design revisions for who knows what reason – maybe its just not ergonomically correct etc. So you can’t ‘not do’ a print entirely, and even the very best printers will have failures sometimes.

      If you can use this sort of scale to recycle it at source and you are a source of any note its absolutely worth it – you instantly cut out vast amounts of road transit to get rid of your old waste and ship in new stock material. Scaled up central infrastructure is all well and good, certainly has a place, but is tricky in plastics as you can’t practically ship only PET, PETG, ABS, Nylon parts separately, or easily split them after shipping to recycle effectively. But in this home/small industrial size unit you can have very good idea what goes into it each time and what the resulting material will be like.

      1. Everything has a cost. The cost (in CO2 or $) of the time to recycle failed prints almost certainly exceeds the savings in the recycled material.

        Just wait until just a little low temp plastic gets mixed in and decomposes to gas in the extruder. Fun for all.

        1. For the small enterprise getting at least all your prototyping done in cheap self recycled stuff is going to work out really good – and those man hours are not likely to be a problem – you feed your mulcher and keep the print farm running all at the same time – its more work in the same hours you were working anway.

          1. Even if the recycling was free (nothing is free BTW). You’re going to lose time to extra failed prints from recycled material.

            Prototyping costs are mostly time (Yeah engineer payrates!).
            Prototyping with crap material is a _terrible_ idea, just a time sink. To save pennies you blow deadlines (and seals…leave my personal life out of it).

            If by ‘small enterprise’ you mean ‘hobby’ then maybe. Because profit/loss isn’t an issue.

          2. HaHa most smaller companies care about not loosing out by wasting of their feed stock, its expensive – miniature casting and jewelry makers for instance are often in house recycling masters, as the feed stock is (especially the ones that make many many of each cast so the sculpting and mold making time barely counts) damn nearly the only cost..

            And with your staff member who would normally be sitting around catching up on facebook or whatever waiting for the next cycle start working on recycling your old rubbish you probably end up with less failed prints – as the operator is actually around to catch them…

            Also a great deal of 3d printer filament you can buy is recycled, some even sold as recycled – it doesn’t make a blind bit of difference most of the time, your 99% pure whatever its supposed to be won’t be harmed meaningfully by that tiny impurity (and really this method should be easily able to get above that – its a tiny assembly its easy to take apart and clean when switching materials, and as its all known materials, being stuff your shop has made you don’t get any ambiguity there).

            Plus these guys are planning to injection mold with it, where it matters so much less as that is shooting the whole damn lot at once, with high pressure through a pretty much unblockable nozzle (as plastic will deform even rather cold at that pressure and the nozzle isn’t tiny), the tiny bead of higher temp stuff left in will matter even less, at most its a tiny defect most likely it makes no odds at all.

            You also have the machine shops – recycling the chips to make new stuff has been done in many materials very profitably (though obviously not always), you often already have the equipment, there is always going to be some otherwise dead time – like when the head gasket goes on a car and the mechanics time to deal with it is worth more than the car – its effectively written off so you trade the junker in, but the shop likely still will do the gasket eventually – The boss was paying the staff even when they don’t have enough paying customer today, so use them to make that heap of junk into a somewhat valuable vehicle again, the part cost you bugger all, the equipment is already there, and the mechanic you HAD to pay anyway and would otherwise be sitting on their arse waiting for something to do…

            NOTE I am not saying this idea is going to be good for everyone, in any possible situation anywhere, but it can’t be so easily dismissed as you suggest as for a great many places this will be by far the best use of their time and money as you can create decent quality raw stock material for the cost of a tiny bit of floor/shelf space, organization, time and energy – where shipping in more can have huge costs – even more so for the smaller players that have to really think hard about paying 10/Kg (and pay extra for handling and shipping probably) to get the amount they know they need or 5/Kg but outlaying 40x more in the hope they actually will be able to use (and store) it all!

          3. Foldi

            I’ve worked for a small manufacturer injection molding shop as _the_ engineer (and machine maint, mold maker, facilities, testing).
            I got tired of banging code after 20 years, now back to it.

            We were trying to do what you say, had been running lots of regrind for years before I got there.
            It was a fucking disaster.

            It made the molding guy critical as he had to constantly adjust the machines to account for varying plastic, by feel as much as anything. He was playing ‘knowledge is power’, but is an idiot.

            I’ve seen injection molding barrels get clogged, the plastic in the barrel decompose to gas.
            The nozzle itself isn’t ‘tiny’, but the gate often is, ours were round with a 0.012 flow gap around the pullpin.
            The machine operator did his usual thing, backed the injector off and put a torch to the nozzle. The clog got _shot_ out of the barrel, sounded like a gun. (followed by nice decomposed nylon…% of phosgene gas).
            He had been running the nozzle temp controller at above the breakdown temp of the plastic…then left it running unattended…which he had been told was a very bad idea…not asking anybody…what did I know, with my fancy book learnin.

            In the end, we found that the ‘money saver idea’ was killing the finances of the company. Massive increase in bad shots, lots of contaminated plastic (we actually bought regrind).
            It was cheaper and better to buy virgin material.
            The regrind came from Michigan (car industry does lot’s of glass filled nylon injection). Half the cost saving went to shipping, another half went to waste material, a third half went to bad shots, a forth half went to machine wear cost, a fifth went to wasted time.

            The owners just didn’t want to see it, using regrind was their idea. But bottom line was bottom line.

            Granting we were molding highly stressed things that barely hold together in normal operation. Not going to dox myself. Only two companies make these in the USA. You’d likely know the name of the companies.

            There is a reason basically nobody runs high% of regrind plastic. It’s been tried, many times. We were shooting nylon, which for chemical reasons is better than most plastics w regard to remelt and keeping its properties, just not good enough.

          4. And as I stated very clearly its not for everyone – but for every job where its super fine engineering margins and tricky to shoot/print/machine parts that really need greatly repeatable known stock you get heaps of folks making what amount to dust covers in comparison – trivially easy to make bulk parts that are vastly over engineered material properties wise as its too impossible even with the best will in the world to use bubble thin stuff..

          5. Also in the case of injection molding you don’t have to, and almost certainly won’t have the material waste generated in house to use all recycled stock.

            So all you end up doing is add in some extra slightly less virgin material by grinding up the failed shots…

  5. Has anyone considered what happens when plastic is “shredded”. I work in a plastics factory, and we have grinders that cut plastic into tiny little bits that can be put back into a molding machine, thereby reusing plastic that otherwise would be burned (runners are not accepted by recyclers). One thing is obvious from grinders-they kick out a lot of plastic bits. Along with the pieces of plastic one can see would likely be lots of microplastics being tossed up into the air. One can see plastic dust all over the place. I clean a surface and come back the next day and see another layer of it. The purpose of recycling plastic is to limit it’s exposure to the environment, but cutting plastic actually accelerates the process, and now it is airborne.

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