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V4 Shredder Single Axis – [INDEX+BLOG]

Friedrich friedrich

V4 Shredder Single Axis – [INDEX+BLOG]

08/11/2018 at 22:25

This is the main blog where the updates for the development will be shared and general questions will be answered and discussed. Beside that, there are a few important sub-topics which I will give you an overview in here:

First a short overview about certain Sub-Topics of the development:

Drives (Motors and Gears)
Cutting Technology (Shredding principles and fine tuning)
Feeding System (Hoppers, Conveyer Belts, new Systems)
Control System (Electronics)


So here the Development Blog starts:


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?

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25/11/2018 at 07:53

alternately. I have also seen someone using a push lawn mover hacked to be a shredder.

Basically you enclose the bottom with your mesh, for example 6mm holes.


the outpout chute is also closed off.


the input chute is fed from the top at a angle so the plastic is not flung out backwards.



14/11/2018 at 13:26



I used an encoder because it’s a simple, cheap and reliable way of providing speed feedback to the controller. The one I used is really simple (made it myself) only 4 pulses per revolution, no quadrature, I just time the interval between pulses, longer than a set time and the motor is bogging down or has stalled. I also put the encoder on the far end of the driven shaft, furthest from the motor, so any problem anywhere along the drivetrain will show up.

14/11/2018 at 11:52

Hi, yes I have seen the saw-blade based “shredder”.
Dave made experiments before the V1 of the shredder already. It is a very inexpensive and tempting solution to go for!

The problem about the setup is that the user has to feed in the material, take it off again and feed it in in another direction. And as soon as you want to divide small granulate into smaller granulate you have a real safety issue.

It might be a perfect solution for flat sheets or to divide thicker pieces for shredding. But overall this solution is not universal enough for our huge variety of plastic.

Have a nice day

14/11/2018 at 05:14

I saw a shredder that used saw blades a couple years ago.  Used in Central America.


Cant find the video anymore.


I did see the video by Jeremy Fielding.  It looks promising but needs to feed from the top thru a long hopper to keep fingers out and flying chips from being flung out backwards

30/07/2019 at 13:20

@papacorn In a broad sense bearings are simply rated by load and speed, so as long as they meet the desired criteria they will be fine. It is however worth considering that the spherical bearing housings commonly used, allow the bearing to change orientation a little and so make alignment and assembly much easier than a fixed rigid housing which generally requires accurate machining and perfect alignment.


With this type of machine it is always best to use ‘fuzzy logic’ so I would say that using some kind of  spherical bearing housings is pretty much a prerequisite


Square bar should be fine, however it is worth taking note that others have had issues with the hex bar set up and the original shredder design. So you might want to determine what sized bar would work best in your application.


With regards to the difference between a shredder and granulator, The PP design is a type of shredder, they are generally low speed, whereas granulators have high speed rotating blades. BTMetz posted a good photo of a DIY granulator early in the thread (I’ve attached it here for your convenience).


Google has heaps of good info on granulator design.

29/07/2019 at 19:46

Deeemm – So refreshing to have you on this thread! Very articulate – love it. Two questions I have for you.

A) Can you explain the difference between a shredder and a granulator?
B) Wondering if there is an advantage for the hex axle rather than square. I have been thinking about using ‘disc harrow bearings’ which would allow me to easily source a cheap square bar. Plus squares are easy to cut with a torch. 😉

14/07/2019 at 16:52

With the rectangular blades, there is nothing to stop them from moving if they come loose, they have no register to locate the insert as you would normally have with this type of design, it is only the bolts that keep them in place. If they come loose, they will damage the stationary plate and possibly the rotor (given that the insert is harder than the rotor)


Considering the cost of the hardened inserts and the complexity of manufacture of the design, as well as the high risk of machine damage if they come loose, why not simply use a one piece blade design made from a high carbon steel that can be hardened on the tooth edge. This has no failure mode relating to loose inserts, and the cost of replacing one entire plate would probably be less than the cost of one insert.


From a risk analysis perspective, if the inserts CAN come loose, they WILL come loose. This means that it is highly probable that for each one of these machines made, it WILL have a failure event where the failure mode is a loose tooth. The worst aspect of this is that the most likely time that this will happen will be immediately after the machine is assembled or shortly thereafter. It should be noted that this probability also increases with the typical contributors – ie inexperience and quality of manufacture – both of which are qualities of your target demographic.


The only advantage that your design has, is that it has replaceable blades. I know that the driver for this was that the blades of the earlier machines had a tendency to wear, but that is simply as they were made from the wrong material (stainless steel) and the blade profile is less than optimum. I think that whilst the general design of the blade profile of the new machine is heaps better than the old set up, they do not need to be made replaceable. It is simply adding extra cost and complexity which far outweighs and perceived benefit they give.


Quick change tooling is only of any benefit in a high production environment where the machine lay on the critical path. i.e. if the machine stops, the entire operation stops. In this case downtime is a problem. However. The usual solution for critical machinery is redundancy. i.e. a second machine.


I think that the original design of stacked blades is fine. it is not a massive job to change one or two blades if there is some damage. And in the case of changing blades due to wear – they will generally all wear at the same rate and so this then becomes a scheduled maintenance issue, which is something that should only be happening infrequently and is also something that you can easily plan for.


Both of these points mean that there is no benefit or even any need for quick change tooling in this machine. It provides the end user with NO benefit.


From a design perspective, your original constraints were to increase throughput and reliability. Both of these are easy to address. For faster cutting you use more blades that have an optimized profile. The optimized profile also helps prevent jamming.


The rotating and static blades need to ‘shear’ the material – like scissors. The old design hooks the material and drags it through the clearance in the plates, this is why it is prone to jamming. Look at any cutting tool and they all operate in the same manner, no matter if they are cutting metal or paper, they all have some kind of shear. This shear also has another advantage – that the point load is only where the blades cross – which is only at one point. This reduces the force required to make the cut. When you use a parallel cutting motion you are trying to cut the entire width of the cutting edge in one go, this requires a much higher force. The angle of this shear is also very important for it to work effectively and is usually material dependant. On your new design, the angle of shear is the angle that the rotating teeth present themselves to the fixed plate – the end of the tooth should touch first.


Increasing the number of cutting edges from two per blade also helps to increase efficiency. Double the amount of cutting edges and you effectively double the amount of work that you can do.


The size of the output is also a big factor. larger shards require less cutting and so can be produced faster.


I personally would love to see a design than could be made with hand tools. Whilst the old design is great and has certainly opened up possibilities, it is still not accessible to a majority of places where this kind of technology is needed. Not that I’m trying to be critical of course, but if it is designed correctly it should be able to be made from either a laser cutter or by someone with basic hand tools. This should be part of the design constraints.


My 02c



26/06/2019 at 20:00

Could you describe what is in the first image (IMG_9762.jpg)?

30/03/2019 at 19:08

There is some development going on at OSE on this as well, so feel free to look there;


25/03/2019 at 23:37

That sounds really good guys! Do you have more pictures of it? Maybe a video?

07/02/2019 at 18:28

yeah, a I am sorry about, i didn’t really start this, I, we just reacted 🙂

07/02/2019 at 17:17

@davehakkens, I think the major problems lies in your way of thinking about the project (see Stan’s comment : i fully agree since it’s 100% backed up by users I had to deal with).

It would be nice if you seek for professional advice, or gain the needed education to build PP as network, flat and of horizontal structure. Enabling the network to grow (see bazar fees problem) and giving the tools needed (see this useless forum software)

Because instead and it’s obvious you’re more busy with building the ‘Dave Hakkens’ brand or pyramid/monolith instead of doing good for everyone involved or at least recognize what’s actually going on with the folks around here. It also looks that anything which doesn’t pass your imagination or doesn’t fit in your box (or mattia’s ) won’t be implemented, supported or sponsored or developed. You can’t be manager, machine builder or designer at the same time. This [email protected] is also another prove for that.

So yes, please find somebody who can advise you in such things; there is a cirtical mass waiting to be boosted. You have received all the funds for that, so please use it for that. Needless to say PP has been a community effort.

what’s required :
– free trade
– budgets for projects (remote, not in f** Eindhoven)
– software to enable networking (what you gave here is just a rotten piece of crap, sorry)
– user – workspaces / show-rooms / bazar
– extendable machine component/catalog
– full transparency: network stats, google analytics, ….
– professional skill sets within the administration – department (replacing you and mattia, please)
– pure community driven decisions, for real.

these things you can find always in open organizations/networks.

07/02/2019 at 13:27

@euromarketo, if you search auction / ebay  / craiglist for ‘plastic granulator’, you can see the range for shredders is 2-5 K. no matter what you have to say about ali-express : a larger manufacture gives you 10000% more for your money. they have solid and pretty cheap supplies and sometimes decades long record to build such machines for and with their clients. it’s unthinkable that a guy in a garage can build the same value for the same price.

, I am happy to see that you finally discovered some basic about community building, so when can we see the first polls ?  And sorry about the accounts, wasn’t really aware that credits is more important than substance here 🙂

06/02/2019 at 17:44

@davehakkens, in real communities, you know, companies, comparatives there is something they call proposals, votes, etc… of course it requires to open up, some transparency, etc… and I wonder if that is soo much an army thing now, why nobody got actually asked or showed what the next steps are and should be.

It’s also not exactly a VERSION – 4. From what I see is VERSION 3 got abandoned and community input pretty much ignored all the way long and what I see in v4 doesn’t fix, meet or improve anything I had or have on my table.

as said, I would have expect more compact, cheap, light, more availability, real improvements, etc.. I bet with you one in 1000 is able, capable, willing to open this container thing/story workspace. unfortunately, we never saw analytics, updated stats, …

just saying, go ahead, see in version 154  🙂

06/02/2019 at 16:04

2K ? can you show us the planned material bill? It might be possible with second hand stuff but in machine builder reality it’s more like this :

1000 Euro only  (we really have good prices) for the drive part: 4KW to call it industrial, VFD and couplings. another 1000 for all the other part, electronics metals and milling/laser service

so to sell that thing on the bazar it’s rather 4000 Euro. For that price, you get MUCH MUCH better on ebay, certified, warranty, security.

Especially if you look at the 3K shredders in the bazar there is little to NO activity. Also, we had not a single customer or request for such larger machine til now (of around 700 requests since the last 8 months). We even tried for a bigger shredder but it’s 2k + is just not the budget of most here.

So again, v4 is getting beyond community and builder reality and all I see is too much fragmentation and resource waste, instead of working for the majority here (small makers) and upgrade v3 you’re getting lost in stuff nobody needs or could effort. sorry

you’re all fired, again 🙂

06/02/2019 at 11:56


It look awesome, we wait a running clip, if it will be possible!
I think is looking very good, professional.

Very good work Friedrich

06/02/2019 at 11:49

And the electronics 🙂


The schematics were created in https://qelectrotech.org which is a really simple program to draw your diagram.

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,

10/01/2019 at 12:20

hoping for an quick update. keep on going 🙂

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


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!


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 😀


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.



16/12/2018 at 22:06

So I’ve gone and bought a VINTAGE 😉 industrial Plastic Granulator. Wortex(now Conair Wortex) HA-811 – made some time in the late 1980’s and she is a beast of metal weighing upwards of 200 kilos.

This machine was designed to be used in conjunction with plastic injection molding equipment that produces LOTS and LOTS of spruce, runners, channels and all the other plastic byproduct pieces of the framework in the molding process that are all snapped off. Because this is good usable virgin plastic it only makes sense for factories to have this recycling stream in the manufacturing process.

This machine a a few main mechanism-
THE AUGER BIT which is chain drive driven by a 1 HP motor with a gear reducer that spins and acts as a screw drive to pull the plastic into:
THE SHREDDER BOX – The part of the machine housing the back of the augur bit and THE ROTARY SHREDDER – which is a big gnar gnar set of heavy blades, belt drive powered by a 1.5 HP motor that spins the shredder wheel at about 300 rpm and smashes the plastic against another stationary set of steel blades.

The guy who sold it to me use to use it for the intended purpose- shredding smaller bits of plastic that can be easily turned through the auger. The hooper is huge and this thing could take a lot of plastic at one time. In NEEDS to be full to properly function. The other drawback is that it DOES NOT self clean. As in there is space in the shredder box out of reach of both the AUGUR what I will call the flat “FLAPPER” and the bottom of the shredder box, also out of reach of the rotary blades. So about two handfuls of plastic just always sit back there in near granulated form. Also below the auger

The machine does produce BEAUTIFUL Pellets pushed through the have iron screen. That also needs more plastic to keep being forced through to push out the pellets through the screen. For my purposes of shredding different types of plastic sorted by color and type these things are draw backs. I called the company trying to get a schematic or manual of this machine and it seems during their merger they misplaced it – though the engineer there did know the type of machine I had and he said that they’ve don’t really make em like this with the auger drive anymore- soooo, confirming what I already wanted to do- I took the auger out and covered the holes with plexiglass – the rotary shredder definitely still needs something like a “Flapper” inside to compress the plastic materials into the rotary blade. I am thinking to fabricate one that will fit in the hole as the same sprocket as the auger used roughly 2 3/8 inches. Looking for suggestions on what kind of steel I ought to use for this piece

orrrrr I’m thinking to upgrade with another set of blades on a shaft in the box. The only issue is there will still be space for the plastic to pool in the back.

My idea now with this giant auger screw I’ve taken off is to possibly make a giant extrusion machine! We shall see…

And I want to replace the old circuit board with a Variable Frequency Drive or some other smaller computer that can control the speed and direction of both motors. Looking for suggestions, please!

Trying to do this before I ship the machine to Costa Rica in January and then fly to go meet it and start shredding all the plastic I can get my hands on.

I will post more pics and videos as this restoration/upgrade continues

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