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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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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 21:20

Let me say that I love the creativity of the brainstorming process. Great ideas here for the shredder mechanisms.
That said, @brettc post was eye opening. Looking at that Aliexpress vendor, they appear to have a shredder that meets many of the V4 goals for $1000 USD delivered to your port. https://www.aliexpress.com/item/Easy-use-plastic-bottle-crushing-machine-shredder-grinder-crusher-shredder-plastic-price-plastic-crusher-price/32851194919.html If that works, building a new machine from scratch may not be worth the effort. I view the PP project as developing an accessible recycling workflow. If one of the machines is already available at a reasonable cost, it is worth investigating. At least obtaining one (or finding someone who has one) and using it as a benchmark for the inhouse development seems like a reasonable path. It may be that the final answer is the modification of one of these machines for different power source, or for cleanliness, etc. It is difficult to develop a lower cost machine that does the same thing as a low cost off the shelf product.

Perhaps the Aliexpress machine is a piece of junk with low reliability, or the vendor is not reliable, or some other problem, but it does set a cost benchmark for a machine of that size

07/02/2019 at 09:06

hmm good point @cgoflyn since we never ask people for feedback before we start a new version, like really never.  After that we always keep our plans super secret, so no one that helps out has a clue what we are going to do. And obviously during the development process nobody can see where we are up to every month, making it impossible to share suggestions. Because we really don’t want people doing that.

But to be fair. YES we actually do have a filter. We listen carefully to committed members, with a real profile (not 5)  that share constructive feedback in a proper way.

07/02/2019 at 10:14

A professional shredder price in my country is starting from 10 K euro.
If V4 will cost 2-4k i think it will be a great achievement. About Aliexpress and Alibaba, i think we all know the stories and the quality. I know somebody with a experience with a Chinese producer and this one provide the product at what quality hi desired – more money better quality, low budget – nice junkie.

Don’t stop and don’t be disappointed. You will not be able to thank everyone. Whoever wants to improve their product alone.

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 🙂

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 17:42

@cgoflyn  that rant was off topic and a bit unnecessary, please start a new thread and refrain from this kind of trolling.

07/02/2019 at 18:28

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

15/03/2019 at 13:10

We made some improvements this month about the cutting technology and started to build up the basic advanced control system for the pneumatic piston.

For now the output looks already promising. We have to continue to improve the reliability of the operation, redesign the blade inserts and the way of how the inserts are shaped and clamped.

Thicker PP material from our sheetpress is a bit challenging for the moment, but we think that the redesign of the cutting unit will solve those issues.

PS CD Cases: 13,1kg/h (old shredder: ~3kg/h)

PS Random Geometry: 9kg/h

PS plates ~10-15mm thick: 13kg/h

PP DVD Cases: 14kg/h

So considering that we are operating at a shredder-with of 1/3 of the full size, we are on a good way to reach our goal of an 30kg/h average.


Beside that we started a second shredder design of a double axis shredder. We want to know which is the most efficient solution (labor/energy/output) in our small size shredders (compared to the ones used in industry).

You will hear about that as soon as the first CAD design is done in the next weeks.

25/03/2019 at 16:10

We are a prototype engineering company in Johannesburg. We just designed a double axial version with the same concept as version 1 shredder but with 3 teeth per cutter. Also we bad the tooth much shorts to the axis of rotation to generate more torque through the cut. we are using a single phase 2.2Kw motor that controlled by our in-house controller that detected when the motor spins to slow (lets say 50% if 1400rpm. I measure with a hall sensor at the fan and glue a magnet on the fan itself. the mass of the magnet is to small to induce a vibration. I was looking at the other alternative to detecting a jam by measuring the raise in current with a simple current transformer.

25/03/2019 at 23:37

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

30/03/2019 at 19:08

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


26/06/2019 at 17:55

It’s been a while we don’t update this topic. We were busy with the development of the V4 Shredder: designing, building, assembling, testing, fixing up, testing again…. So I want to say sorry for that. But it means we have lot of news to tell you about the Single Shaft Shredder development!! We finished and tested the single shaft shredder with triangular blades and rectangular blades.

Triangular blades were hard to manufacture and during the tests some teeth broke because they were not properly welded. Besides, some big pieces of plastic could pass through the rotor (the design has to be improved).

Related with the rectangular blades, they are Hardox 400 made so they were really hard to work with them (drilling, threading). So we decided to weld many of them. The blades that were not welded worked properly.

26/06/2019 at 18:52

apologize accepted; just don’t do it again. normal science work involves around 40 hours on the job, 20 hours to publish a new paper and another 20 hours for volunteer activities whilst still working on a few pet projects.

yes please, no hardened steel; mild steel can be processed and hardened on demand; in this case easy to grind or cut a knife mount and weld or bolt a grinded HSS blank on it; easy also for our buddies in the more urgent countries.

26/06/2019 at 20:00

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

26/06/2019 at 20:47

The performance with the rectangular blades was very good, shredding around 16kg/h (with a 140mm width shredder, not bad). We did the test without a sieve and the size of the flakes was quite good. However, there were some big flakes of plastic, but it can be solve by installing a sieve.


Some conclusions drawn from the test:

– Hard to adjust the gap between blades and static blades with the current design.

– Good size of the flakes with thick plastics.

– Some big flakes with thin plastic (bottles).

– The performance and safety increase with a inclined plate (15 dregrees) for the piston.

– Use normal blades (like double shaft shredder) makes simpler the building process of the SSSS.

– It can shred big pieces of plastic, like sheets or beams.

– It never got stuck during the testings.

– Some pieces of plastic can reach the back of the piston


During the tests we measure the current consuption. In some moments, the motor could consume up to 8-10A max, but typically 6A when it is shredding plastic. The nominal current of the electric motor is 6,9A, so the 3kW motor has enough power for the shredder.

27/06/2019 at 21:34

@s2019 the first image is the rotor for the triangular blades. I have changed it for a better one.

27/06/2019 at 21:52

Thank you, much clearer

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



26/07/2019 at 19:04

Thanks very much @deeemm for the feedback. We appreciate it so much!!

One of the conclusions drawn from the test is:

– Use normal blades (like double shaft shredder) makes simpler the building process of the SSSS.

Totally agree with you, we think is the best option. As you can see in the photos, the last version has blades without replaceable teeth.

You say that “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.”

That is what really happens. You can see it in the attached photos.

I have also attached a photo that shows the three prototypes of the shredder we have developed so far.

27/07/2019 at 01:25

Just reporting back on my development here.

After sharpening the v3 blade teeth to a sharp chisel point, and the 1.25 inch hex shafting with 25mm bearing.  Upping the power to 5hp.

I am getting 50 kilos of bottle caps shredded on the existing design.  However this is without a screen.  I have to feed the material thru a second time to cross cut the material.  It still does not like pet bottles much without crushing first.  The blades wont grab it easily.

My double size shredder on the other hand grabs pet bottles nicely.  Same 5hp motor.  That machine has been running 4-8 hours per day for 2 months now at a plastic foam factory.

My other clients who shred mostly sachet do not get 50kg per hour.  Mostly due to the bulky nature of the plastic.  They feed the hopper as fast as they can with big handfulls of material.  It digests plastic bags nice too.

So far jams result in the belt spinning not the motor stopping.  On 2 latest machines, the belt is very tight and no jams despite over feeding it.

The use of a 63 amp transfer switch to reverse the motor has made life easier.

Initial supplier ripped me off with a german switch that cost 90usd.  I since found indentical China switch for 15usd that i imported.

27/07/2019 at 03:45

Nice work. I’ve had some more progress on my own development that I will share…


The second cutting action on the underneath is very important and often overlooked. The first pass through from the top of the blade(s) cuts the plastic up, but it is the second blade underneath that cuts the shards to size so that it can fit through the screen. On the orignal PP design, there was no lower blade, the plastic had to return to the top blade to get cut to size. Essentially it had half the capability it should, which means half the throughput. Most dual blade shredders have this second blade (the plates to the outside of the blades.) Many commercial shredders / granulators have multiple static blades. Also, the clearance between blade tip and screen is usually about 1/8″ on commercial machines. No cutting takes place against the screen.


The size between the tip of the blade and the root of the rotor was very large on the original design, so the granule size was very large (it actually tore it into strips more than cut into granules). This also meant that to reduce the size of the strips they had to fit exactly in the right place on the blade and not between the blade tip and rotor root. This would then become more a game of chance than by design, which meant that the granules spent longer inside the shredder waiting to get cut to a size that fitted the screen.


My application is slightly different to yours in that I’m aiming for small (<6mm) size as I’m 3D printing direct from granules, so I’ve been focusing on the size, however, I think that the same principles apply to increased throughput.


If the size of the plastic after the first pass is small, then it will probably only have to be cut by the lower blades once to reduce to a suitable size to fit the screen. The key is to ensure that the space between the tip of the blade and the root of the rotor is small (like on your single blade machine or on my design – see photo.)


It is also important to ensure that there are tight clearances between the fixed and rotating blades. If you are shredding milk carton and it is only 1mm thick, your blade clearance ideally needs to be much less, this prevents the material getting pulled through in between the blades and causing high loading to the motor. This action is not actually cutting the material it is stretching it – plastic is very strong in tension, It will stretch a long way before it yields, this is why the original PP design jams / trips – as the blade clearance is massive and plastic gets drawn in between the moving and static blades stretching the material. This effect is lessened with dual blades and both blades move and so the material does not have to stretch until it yields. The only issue with making a machine that has close blade tolerances, is that the manufacturing methods change and cost of the shredder increases. (Ground plate is required to control blade thickness).


There are also consideration to the feed object size relative to the desired output size. I cannot take a large plastic object and reduce it to a sub 6mm size. there is no way that a blade like this could deal with say an extruded beam and efficiently produce a sub 6mm output. Optimum blade characteristics lean towards larger granule sizes when dealing with larger input size, which is okay when used by larger machines. like the rest of the PP machines. There is probably an optimum ratio relating to input size, rotor size and required output size. I think that the ideal machine for household waste is not the same machine that you need for processing plastic beams, if the same design is used, there will be a tradeoff.


With all of this considered, I have actually come to the conclusion that a shredder is not appropriate for my specific application. My focus is now on a granulator design. In all of the plastics companies I have worked (injection molding / blow molding) none used shredders for reprocessing waste, all used granulators, and some processed large, thick material into a relatively small pellet size (from 800mm x 600mm x 15mm thick irregular shapes, down to 8mm – I think a much better ratio than a shredder can achieve). I think that it is also easier to make a granulator and requires less close tolerances and so are much easier to assemble. Additionally no gearboxes are required and there are less parts, so cost is most probably less.


I think shredders have an instant visual appeal and they have a definite attraction as they are very satisfying to watch, but I’m not 100% convinced that they are the most efficient / appropriate choice for this application. It’s funny, but having worked with granulators for many years I never really felt any excitement about using them for small scale recycling, but after seeing shredders in operation you get a bit excited at the prospect of making one. They are awesome / formidable bit of equipment and they get people excited, but I think a granulator is more appropriate. I am very surprised no one has tried to make one.


My granulator design is pretty much finished but is not formally documented. It will be released open source when it is done. I’m happy to collaborate / share with the PP team if they have the resources to take on another build. @davehakkens if you are interested, shoot me a PM to discuss.

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. 😉

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.

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