We've just launched our map. Add yourself by clicking here!


v4 Shredder Development

This topic contains 52 replies, has 23 voices, and was last updated by  Ionut Socol 5 hours ago.

Friedrich friedrich

v4 Shredder Development

08/11/2018 at 22:25

Hey community,

I’m Friedrich from Germany – a Industrial Designer and Engineer. I will work on the next revision of the Precious Plastic shredder in Eindhoven until the beginning of the next year.

As most of you know there are some things about the shredder which can be improved to build a more reliable/productive and safer machine. The recent weeks I ran some tests with the current shredder, a fast-spinning shredder and a double axis shredder to compare them against each other.


Some points which we are sure we want to improve:


Right now we have a max output of ~10kg/h – to run a workshop or small business with our shredder we need at least 40-50kg/h. The goal should be to shred in half a day (or less) the complete plastic for a week.



The next version should not jam that often as the current shredder does. This is not just a problem of the motor power only but also concept related. Furthermore we want to implement automatic reverse (Torque detection) and back to normal operation.

This is very related to the topic of reliability, due it is not possible to build a save shredder if it is not processing the input material in a reliable manner. The shredder should run without any correction of the user during the shredding process. The shredding blades must not be accessible during the operation, this is ensured by mechanic constraints or sensors.



Some of you report a fast wear down of the shredding blades. The new version should have a way to reduce the necessary time for maintenance and changing of blades. I will try to increase the lifetime of the blades by optimizing tolerances, cutting angles and material selection.



The revision of machines will come with a guideline for a easier part-selection process depending on personal needs.



So how will we start? 

Our biggest problem right now is the huuge variety of plastic we recycle – small/big, thin/thick, flat/geometric and different materials. And most of the shredders are specified on one particular task. E.g. slow running Granulators to recycle runners of the injection process.


I found a different concept from our existing one which i want to adapt to a smaller size shredder. I think it can solve the problem about the big variety in the best way. The biggest benefit of this shredder type is that, the process is more reliable and you can throw in even bigger rests of plastic like left-overs from the extrusion machine or half injected parts.


Its called single shaft shredder which looks like those ones here:


Of course our shredder will be a bit smaller 😉

The build will be similar to the current one (stacked blades on a hex-shaft) – just the blades will be between 10-20mm thick, to assemble the teeths on them. The width will be the same for all, but the length will be adjustable to your needs (education vs. production)


What do you think about this concept?

52 replies
24 subscribers
6 saved
sort on most likes
13/12/2018 at 11:54

more pictures here.


As you can see the blades are only leaf spring ground on a angle grinder.



14/12/2018 at 00:21

@btmetz I think you might be talking about my friend Recycle Michael of WasteBusters and I turning his old electric lawnmower upside down and screwing a metal trash barrel to the top? Worked decently well one we changed out the single flat blade for some flimsy sheet metal ones we were able to bend up. We did a cross of the two sets of bent blades and screwed them on opposite one more bent up and the there down like you would see in a normal blender. It worked pretty well for blowing apart milk jugs when we tried it. We quickly moved on to the next thing. I’ve been meaning to do an instructable…still do…

some instragram videos below


Love + Trash,

14/12/2018 at 12:16


Ohh wow, thats a nice one!

I would really like to have a look at your CAD Files, will also share mine below. Could you send yours to [email protected] – thanks a lot 🙂


So you use two motors in your design? Looks quite narrow space-wise^^

I like the idea of a belt drive to add some additional spinning mass to the shredder blade axis. Especially the opening drawers on the side seem like a useful addition to a shredder, so maintanence and inspection is easier this way.

I think the main issue is, as earlier mentioned, that the process of shredding is not a predictable one – you throw things into our shredder, but you never know if it will be shredded by itself or if you have to push it or even stop it and reorient the piece.


After this stage I will have a closer look by testing in multi-stage shredders and try to give an evaluation for it. Not sure if it makes sense, because its always hard to define a testing-pattern, but let’s see.

Its true, there is no CNC machining in some places, so i try to stick to already proofed technologies like laser-cutting. Making a high end Shredder Shaft based on 5 Axis CNCing would be a easy one^^
But also in prototyping and testing you want to go as fast as possible – optimizing for rebuild is another step i think.

Here are the CAD Files of our new Proof of Concept Prototype. Feel free to download and comment on them.

Please don’t redistribute anywhere else online, to make sure its clear that they are under development and not final in any manner.



Greetings – Friedrich

14/12/2018 at 13:33

Regarding the hex or square or keyed shaft, I though that having a round shaft where all the parts are bolted together might be a good option. The end piece would be a gear or pulley also bolted through. A gear could easily be laser cut like the rest of the blades, therefore the bolt holes easy to locate. A spacer on either end gives clearance for the bolt heads and a bearing outside of them. A large gear/pulley would contribute to the gear ratio needed for the pp shredder with most off the shelf motors.

15/12/2018 at 02:42

btmetz – I like those photos – and I think using spring steel is a great idea for the rest of the world. Dont have a laser cutter, just a torch and a drill press?  Even auto/truck axels are decent, because they have splined ends. Splined ends could be mated to pulleys, or at least ground down to a specific profile, using the splines as a guide. This is what I read recently to make me think – I likey…

“Truck and Auto Axels have been a favorite for making hardies and hammers as they are one of the largest pieces of forged steel on an automobile. Note that the flange on some axels is the perfect shape for a mushroom stake with a little work. The splined end has been used for texturing. “

Grind them down for the blade, and maybe even use them as the axle of the shredder? My first world mind still loves the idea of using carbide though…

15/12/2018 at 11:38

I like that upside down lawnmower.  although ll bet some curved leaf spring two pieces, and curved one up and one down so same arrangement and sharpened would work too.

18/12/2018 at 02:22

I like the replaceable teeth idea, one thing I’m not sure if you have considered yet or not, would be creating a tooth design compatible with a current commercially available industrial shredder so that we may either create the teeth ourselves or purchase the OEM teeth ready to go.

I dare say no premade teeth would be particularly cheap, although they would be made to handle industrial loads AND in some countries if fabrication availability is an issue, sourcing a commercial product might not be.

20/12/2018 at 04:17

I have been meaning to share this experience- and the last time I typed this all out the post was lost so….I shall tell the story again!On Black Friday November 23, 2018 I purchase a “Vintage” Wortex HA-811 plastic granulator made around/before 1989- that I found searching the keywords “shredder” “grinder” “chipper” on Craigslist- and now will add “granulator” to those terms . This machine is a BEAST- weighing somewhere between 600-800lbs. It’s output is tiny plastic granules that can be used easily with plastic injection molding machines. This machine is intended to be used in conjunction with injecting equipment in order to shred up and recycle into usable grains once more all the spruce, runners, channels, and all the other plastic framing that is involved in injecting plastic parts. The parts are usually snapped off this perfectly good virgin “waste” plastic which is then thrown back in the granulator to be recycled.

I checked the website and called the now “Conair” Wortex manufacturer and spoke to someone in the service department who was familiar with the type of machine I had though could not locate the manual for it. He could only send me a questionable wiring diagram that told very little. He did tell me that they steered away from this design of plastic shredder due to the big bulk auger bit which I will get into in a moment.

The machine has some main parts – THE HOPPER which is the huge inverted rectangle thing above the outstretched right arm- THE AUGER ASSEMBLY. Inside the assembly is the AUGER SCREW which is turned by chain drive by a 1 HP motor with gear reducer which spins at about 70 RPM. The auger screw turns thereby “pulling” the plastic into the SHREDDER BOX which is full of the aft portion of the auger screw after it stops spiraling and becomes just a straight “FLAPPER” as I have grown to call it. The FLAPPER and AUGER SCREW are very much the same piece of metal.

Inside the SHREDDER BOX is a ROTARY SHREDDER comprised of massive blades that turn belt drive by a 1.5 HP motor on a separate switch and directional control than the AUGER MOTOR. The ROTARY SHREDDER spins at WAY more than 100 RPM and takes plastic that is pulled into the SHREDDER BOX by the AUGER SCREW into the FLAPPER and is smashed into two STATION BLADES, one on the top one on the bottom. You can peak into the top of the machine by the TOP ACCESS DOOR to the SHREDDER BOX above the FLAPPER. The plastic is then forced through the bottom where there is an IRON GRATE/SCREEN that plastic is pushed through into the form fitted BIN that also has a vacuum attachment(I will get ideas for this later).

These existing assemblies have some serious draw backs. As the AUGER SCREW does it’s thing it also plays a roll in the smashing of the plastic to smaller bits. The guy who sold it used it for it’s intended purpose – shredding lots and lots of small little plastic spruces and getting grains out of the bottom. The machine LOVES TO EAT!” He told me. The more material you have in the machine weighing the bottom material into the AUGER and filling up the SHREDDER BOX – pushing more plastic against the ROTARY SHREDDER as the box is full. I ran the machine with a good amount of material and getting great grains for some time until I ran out of material to feed it.  I let it keep running and realized- as expected- Some of the bits will ALWAYS sit in the bottom of the AUGER ASSEMBLY as the screw is unable to “self clean” the area due to lack of contact aka a clearance of maybe 2 milimeters or .5 Inch. Also as the ROTARY BLADE does it’s thing and the FLAPPER turns feeding it more and more plastic there is also some clearance at the back bottom of the SHREDDER BOX leaving some room for plastic to pool and sit as well. The only way to clear the machine completely out of plastic is to shut it off and open compartments and do it by hand. A big drawback in my opinion and for those wanting to change between shredding different types and colors of plastic.

Since the machine is super bulky and these assemblies fall short of doing what I need my idea was to take the HOPPER, AUGER ASSEMBLY, AUGER SCREW completely off, which I have done. I covered the holes left by the AUGER ASSEMBLY and aft drive shaft which fits the sprocket for the chain drive with some PLEXI glass because it’s what I had and I wanted to be able to see in the machine. I ran the machine with only the ROTARY SHREDDER going, feeding from the TOP ACCESS DOOR and as I imagined it would – the plastic pools in the empty space left by the FLAPPER in the SHREDDER BOX.My idea is to customize my own FLAPPER. OR just to use another set of ROTARY SHREDDER BLADES on a driveshaft and fit it into the existing sprocket and bearing combos. Looking to do this drive shaft out of an upcycled car axle though also very open to options of what kind of steel I could use for this experimental FLAPPER. And also just the idea of adding another shredder stage on top sounds really good to me.

If I stay with setup I will be building the NEW HOPPER up off the TOP ACCESS DOOR which I have seen in most newer models of this machine.I also have the idea to swap out the big bulky ELECTRICAL BOX which houses the motors’ switches and relays for a smarter, more compact Variable Frequency Drive or something else. Both the motors are 3 PHASE, 220 volt, right now I am running them through a digital phase converter and plugging into the standard dryer 220 v plug in my grandfather’s garage. Looking for any and all advice/expertise on how to effectively upgrade this box, please and thank you!

This machine has about 2.5 inch solid plastic casters(wheels on it) so its decently easy to move on flat smooth services with a single person. One day I’d like to make a towable plastic shredder on a trailer, much like a large woodchipper that can be towed to places and events and shred plastic on the spot. Or perhaps I just upcycle a different vehicle like a golfcart or ATV and make the shredder itself driveable. I am very happy to be involved and see so many involved on these v4 shredder discussions!

I want to share my experience in the upgrading of this old model shredder in addition to having helped build a PP v2 shredder and intending to build a v4 dual axle shredder very soon. I was looking into doing this and then found this shredder on craigslist for $850 and after buying the digital phase converter and having it delivered to house, buying a new plug and some wiring, greasing the bearings I’m only into the machine about $1100 – which is a big hunk of steel and shredders and motors and wiring that already does a good job of shredding plastic which I intend to redesign to make better. There have been thousands of these machines so maybe our project will create somewhat of a following around restoring and upgrading these vintage type machines.Thanks to all those who took the time to read and anyone that is contributing to Precious Plastic! I will post more updates.

Love and Trash,
Garrett Cadou

20/12/2018 at 07:00

The type of OEM shredder blades I am looking into getting.

Two different types pictured and a nice little video of how this company WANROOETECH water jets there own:

20/12/2018 at 11:33

Thanks Garett for sharing this manufacturing Video 🙂

Yes I consider this option, however it’s a bit difficult because if you rely on commercial available shredder inserts, they are not standardized as far as i know…
Means that you can only buy those parts from one company (as long as they support their product).

20/12/2018 at 12:55

@gcadou  I have been using a kitchen blender and was thinking of scaling it up with an angle grinder as they are easier to get than an electric mower. It seems like the cheap and easy build.  The blender blade design is needed to keep the plastic mixing.

I was also looking at buying a plastic shredder from aliexpress  but I can’t afford the $2000+nzd  and the 2nd hand market in New Zealand for these is empty.

The CNC cost of the precious plastic is also beyond my budget,  so have been looking at alternatives for that style of machine.  I was thinking of something like these milling heads at around $20 each might do, if a number are combined into one shaft.  Or a Woodworking Finger Joint Shaper Cutter  <= which could cut its own key(?- the grooved slots that the blades pass through and the plastic doesn’t).


So many options,  I might start with the angle grinder blender because it’s easy even if it requires more operating time in loading and unloading the bucket.

21/12/2018 at 02:08

friedrich – Material selection is key here, 304 is by far too soft. For the cutting teeth, have you looked into taking a commonly available grade of steel that can be hardened, low carbon steel (AISI 1018) or alloy steel (AISI 4130) for instance, and heat treating the cutting edge by quenching after localised heating with a flame torch? Another method to get a hard wearing tip is hardfacing using a welding setup (MMA is cheap). Saw these comments made by bastelmike, servant74, micro and tatheta elsewhere on the forum. Also, forming the teeth before heat treatment to a chisel point, as I saw justinc mention in another thread, will help with wear. This can be done with a simple file.
I can help you out here if you want, got a fair bit of materials selection knowledge, especially with metals.

brettc –  If you go along the route of the milling cutters look into ‘gang milling’, and cutters associated with that, they can be set up on a single axle with or without spacers. Depending where you are you might find a machine shop that just has them ready to give away / throw out / sell cheap, it is an older method from before NC.
You’ve got me thinking, could get 5mm gang mill cutters and replace the cutters in a Precious Plastic shredder, might help with the wear..

21/12/2018 at 07:10

I did some research on the finger joint cutters.  I see that the standard size is 160mm with a 6mm thickness.  they are kinda expensive though.  Possible instead just TIG some leaf spring bits to the end of the existing blades.


Alternately there are wood plane cutters that are ready to add into a hopper feed mechanism.



23/12/2018 at 12:48

hey guys,
@btmetz shared some photos of a high rotating shredder. we build one pretty similar – just smaller. This shredder is working great… even with a power of an bicycle! We have 4 rotating blades and 2 fixed on the casing. The blades are out of hardened steel. We focused on that design because it’s working more like the industrial standard, which is high speed (about 1100rpm). It doesn’t need that much power. Successfully we tested a motor with 0,3kW/230V and a 28″ bicycle.
We doesn’t made an exact comparison test, but we think that this design is working more efficient than the current pp shredder. Another good benefit is, that the plastic isn’t that much electrified. This was on of the main problems we struggled with the current pp shredder.
At the moment we try to simplify our construciton, especially the axle.
I’ve started a topic in the forum, but it’s been a few weeks since I posted something. But there will be a video in the next few months about the building time and the cad files are also nearly finished…

great topic!


23/12/2018 at 14:59

hello there .
it is so nice to see that many designs . everyone has an a littlebit other approach to shredders. I wanted a shredder wich caould work still with an motor 1.5kW -2.2kW but bigger. And I made something . actually the very first prototype is being buildt rigth now. it should be able to process about 150kg of plastic per hour.
But it would be made out of thick plates of steel – 25mm , blades from 16mm thick stell. it would be rather 4times big as the pp one.
Ill post ,more of it when it will be buildt. we will see.

for me the most important thing was to build it ASAP   – As Simple As Possible 😀


07/01/2019 at 04:19

Did some work on shredder blade design with my friend Max who is a sophomore at the University Central Florida in Engineering and helps look after the Fab Lab here in Sarasota, FL when on winter break.

Here’s the google drive- open source!


07/01/2019 at 06:20

Hey @kunststoffschmiede that design it’s awsome. I would love to start developing something like that here in Argentina. Are those files and experiences available? Would be great if our team could continue your footsteps between now and March, when we start with the University’s work.

07/01/2019 at 17:18

hey @leoroth
thanks! we are still working on a proper documentation. I think we will publish the video and the files during february. furthermore you can contact me personal via direct messages and i will give you some unpolished files, so you can start to work on that shredder!

much love


09/01/2019 at 19:50

Small Upgrade: Parts arrived


The parts came just before christmas, now some smaller bits and pieces are purchased.


The Cutters were a bit challanging to layout for lasercutting, but turned out quite nicely. However the clamps were too small, so they bent during cutting and everything got burned.

We will go for the easiest replicable version first and add another blade type later for readymade inserts or “professional made” blades.

Parts are cleaned from lasercutting and next is to weld everything together, build a frame for testing and set up the control box. The goal is to get the unit ready for the first tests in the end of next week.

Will keep you updated about the process 😉

10/01/2019 at 12:20

hoping for an quick update. keep on going 🙂

20/01/2019 at 10:38

I really like the thought process so far. My biggest concern is cost mainly in getting cut parts. I’ve been trying to find somewhere local to do it and only run into ridiculous pricing in the thousands of dollars. And that’s without trying to find the motor or someone that can weld etc. Most places that have the equipment to cut parts won’t deal with anyone that wants to do a one off small projects. (I’m in Indiana) I am moving to a different state soon though hopefully I’ll have better luck.

22/01/2019 at 02:08

Hi Friedrich

How the project work?
I’m looking forward for this and hope everything will be just fine!

Congratulation for all your work! I admire it and wait to see the final phase!

Best regards,

Viewing 22 replies - 31 through 52 (of 52 total)

You must be logged in to reply to this topic.