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V4 Shredder Double Axis – [INDEX+BLOG]

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This topic contains 41 replies, has 11 voices, and was last updated by  Michael 2 years ago.

Yann lagrenouille

V4 Shredder Double Axis – [INDEX+BLOG]

23/04/2019 at 15:49

Hey community,

We are 3 guys to work on the V4 shredder double axes, Landry (@landry) from France – a industrial designer and engineer, Paco (@pacoacu13) from Spain – mechanical engineer, and Yann from France – material engineer.

We work on the Precious Plastic shredder double axes in Eindhoven, and we try to find the best solution for shred some big parts of plastic, also including thick parts like beams and sheets.

The sub-topics will be the same than for the single axis shredder, as most of the technologies will be similar :
Drives (Motors and Gears)
Cutting Technology (Shredding principles and fine tuning)
Feeding System (Hoppers, Conveyer Belts, new Systems)
Control System (Electronics)

The double axes shredder is the most used for different industrial activities, but with different designs for different results. We need something close to an industrial shredder, who can shred different plastic shapes and sizes quickly, and easly in very little plastic chips.

Reliability, Safety & Maintenance
As for the single axis shredder trials, the next version should not jam as often as the current shredder does. Furthermore we want to implement automatic reverse (torque detection) and back to normal operation.
Safety will also be improved by a proper hopper limiting the acces to the blades, and a good “catch” of the plastics for removing any human help in the process of shredding.
Maintenance such as cleaning (between different plastic batch) shall also be considered.

So how will we start?
The main goal we want to achieve, is increasing the shredding capacity, we want something much bigger than the last verion, and that can work all day (at least 7 hours) with no jam and very few human interventions.Our biggest problem right now is the huge variety of plastic that can be found – 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.

Double axis shredders in general seams a very polyvalent option, even if they have quiet some incovenient (like a lot of laser cut parts…), but let’s give it a try at least !

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23/04/2019 at 22:22

@lagrenouille , I am glad you were able to assemble a team of trained engineers to tackle the complex shredder development. Could you post the list of quantitative requirements your team has developed for this shredder development? Have you selected a benchmark for the shredding capability? How does the V3 shredder perform against the benchmark? @andyn has a great looking, small dual axis shredder, perhaps he could tell you how his machine performs against your benchmark and what the lessons learned are. Looks like you are upsizing the shredder into the range covered by the smaller commercial machines. Do they meet your requirements? Do you have a price target for your shredder development? How much cheaper than the commercial units will it be?

I think for those of us who have not gone through your planning process, some of your background research would be very helpful if posted so we can understand the scope and rationale of what you are undertaking.

Thanks for your efforts, looking forward to your results
Good luck

20/07/2019 at 10:28

@landry When will we get our hands on this?

31/05/2019 at 18:11

I really want to see that v3 update, since I (like a lot of people) have this machine and I would like to take advantage of it as best I can.

02/05/2019 at 18:03

Hey community,

We have start the test of the double axis shredder, we will try different sheet with different thicknesses and compare the result with the single shaft.

We have decided to try with cutting blades to test the capacity of the shredder to grip the sheet.

Then, we will check if the flakes are enought small for be injected or compressed without re-shred. We will check the good point and bad point of the double axis (price, easy to build, powerfull, speed…), if we can do much better with flat blades and we will compared all that with the single shaft.

24/04/2019 at 00:01

Yeah, I’m always surprised to see people post “hi, I’m new to PP, I want to get started, I want to build a shredder” why? Unless someone thinks they can market plastic flakes (which may be viable for the artist market), the shredder does not produce a product.

I do think there is value in PP maintaining a reference buildable shredder design. I assume there are situations where someone has surplus metal available to them, a torch, grinders, some basic shop tools, perhaps an IC engine, limited cash but has some time. They can adapt the design and get something going without the cash obstacle.

23/04/2019 at 18:46

@pporg thanks for the info

About the v3, i haven’t worked with or talked to the team in Netherlands so I don’t know what their thought on v3 are, but from what I gather is shredder with v3 design was as good as it gets and to troubleshoot the main problems ie clogging and speed there is no other alternative than to switch to a double shaft shredder, which meant going back to the drawing board and changing the design.

Again I don’t speak on behalf of the Netherland team, but if you think that the current design can be improved by consulting some seniors in this field then you should definitely go for it instead of waiting for someone’s approval or permission from Netherlands. If they take and implement that feedback is for later to worry

23/04/2019 at 17:12

hey community, the final model will look something like that

23/04/2019 at 15:51

Sorry, for the multiple posting, we struggle a little to upload.

Here some additional pictures 😉

21/08/2019 at 11:56

Hello guys, we have design and manufacture the double shaft shreder. Here is our machine

21/08/2019 at 00:54

How is progress coming?

05/07/2019 at 17:09

@landry I like your Shredder, is it possible to have a futur of this one. Is it the next download kit?

27/06/2019 at 22:35

So, what we need:

It needs higher torque: it get stuck with cd cases and big HDPE bottles. We want to keep the same power (around 3kW). That means we have to lower the speed to get higher torque. So we need a higher ratio for the gearbox. New blades: Flakes are too big. More teeth and less thickness Hard to clean: The flakes can accumulate in many places of the shredder The gripping is not good: sometimes the shredder can’t catch the plastics. Easy to build: Keep a design easy to assembly with part easy to find.

In the double shaft shredders, the size of the flakes is determined by the number of the teeth and thier respectively width. The new design of the blades is mainly focused to get small flakes and to have a good gripping as well. So we design a shaft with 13 teeths/blade (small flakes) and another one with only 6 teeths (good gripping)

We made also something very easy to build and assembly, we have also include the gears inside the box for more safety

And we have also increase the output and decrease the speed of the motor for answer to the stucks problems

For the specs :

Size of blades: 6 x 130

Shredding dimension: 240 x 300


Power: 2,2 Kw

Output speed: 19 RPM

Nominal torque: 1000 Nm

So we make this new design:


27/06/2019 at 22:11

Hey community :

For this shredder we have a 3 phases motor with these specs:

Power: 3kW

Output speed: 65rpm

Nominal torque: 440 Nm

Gearbox Ratio: 1:21,43

After building the first V4 shredder, we have test it during 2 weeks with differents plastics :

PP : Sheets, DVD cases, buckets…

HDPE : Sheets, Bottles, Buckets

PS : Sheets

we have drawn these conclusions:

The most big problem we can see during this test is the thickness of the blades, 10 mm make big flakes and the motor is not enough powerful for shred everything. Also the design is not easy to build.

31/05/2019 at 18:37

@sacrys, there will be some updates from PP Catalonia for shredder v3: less dangerous sieve, easier assembly, 32mm hexbar, 30mm driveshaft, bigger bearings, some modifications to have the hopper mount in place, blade changes, a few minor updates about the holes and a bunch of framework variants: school version (more safety), portable version, extrusion combo. Also we have a solid and well tested wiring plan with auto-reverse. of course with fixed material bill and new laser files for different hex-bar sizes (28 – 32). i just had no time to upload all yet.

07/05/2019 at 18:42

Good, it looks very interseting!
The differents tests does with the doubles axes make the plastics chips to thicks. That because the blades are not crossing enought, like the Fig 1 on the picture. We need to cross more, with larger diameter blades and smaller diameter washer, change the the space between the 2 shafts like the Fig 2 AND change the thickness of the blades, for 6 or 8 VS 10 for the prototype. In this case, it will be a little more long for shred plastic, maybe we will limited on the plastic thickness, but the flakes will be, for sure, smaller.

Guys, let me know your opinion 😉

For the final version, if we choose this version, the idea it’s make something easy to build, with the minimum weld, screws… for give the possibility to build it everywhere with the minimum tools. if you are some idea about it, let we know here 🙂

24/04/2019 at 12:15

@s2019 you are right, this should actually be the starting communication point, I will put these datas in a presentable way, and post then soon.

We also have here a shredder similar to andyn’s, small double axe, and it works quiet well in various situation. This is a kind a scaled up machine. Might make sense for some situations, not for others.

@pporg to answer some of your questions / remarks :

– The shaft is 36mm, like for the single axis one. I think I remember you said 32mm might be enough on another topic, but we choosed 36mm as it seamed to be worldwide available. Anyway we try to make the drawings parametric so it can be more easily adaptable to what’s available.

– Concerning price range, yes we are aiming for something around 2-3k of material, which unsurpringly put us in a selling price range of alibaba shredder. Not more expensive though, for 1-2k you only have a peletiser, in which a strongly disrecommand for thick plastic.
We don’t say to anyone to mandatory make this one. We offer an alternative. Then it is up to everybody choises. And additionnaly, this is only a prototype, that can very probably be priced imporved.

– Also from what I read on some of your post, you seams deeply involved in opensource projects since a while. So I guess you get the principle, we don’t have this 30-40 years of experince some manufacturer might have, but we have a large community of competent people like you seams to be, that can debug, redesign, adapt… that allow us to be faster than any industrial plant.

– We try here a bigger version to imagine that people can make a living only out of shredding plastic. Might be an illusion or an utopia, but it might make sense for some people. For the others, there is others solutions.
Same apply for the small one, we propose one solution / one alternative. It might not be adapted in all case neither. But we trust on intelligent people to built it not exactly the same but adapted to their needs / means.

Then this will be my only answer to the polemic of the need of a bigger shredder. It doesn’t make sense for you or others, fair enough. Let’s keep this topic to find the best way to do this one, and at the end, we can see for who it makes sense (if it does even, maybe ?).
I would really like your inputs on the way to design and built this one as you seams very competent, but if you feel like we are only wasted time and money, then I’ll don’t waste yours.

23/04/2019 at 21:05

and here the current times for v3 :
– turning driveshaft, key way (need a shaper for 2K), 2 hours
– grinding blades and washers, tips 3 – 4 hours
– welding 3 mm sheets and cleaning up the mess you get on stainless: 2 hours
– making sleeves to compensate nominal sheet errors : 2 hours (those washers in the kit are pretty useless)
– making the support blocks to host UFCL206 bearings via M14 screws, 1 hour, obviously it doesn’t take long to realize that a M10 ACME/bolt holding 200 – 600 Nm isn’t exactly appropriate here, is it ?)
– turning hex bar on size, 2 hours ( you need this precise as possible )
– assembling the shredder 1-3 times til all fits nicely, 3 hours
– making the frame, incl. paint, 4 – 12 hours, depends on wheels and other things you need for the youth/school
– wiring all, breakers, emergency switch, powerplug, 4 hours
– compensate errors til her : 2-3 hours
– making the hopper , 4-6 hours
– testing and fixing : 2 – 6 hours
– logistic : 3-5 hours
– couplings: 1 hour, 2 hours loud CNC

That are my times, with pretty much the best tools you can get for this job. My students need near the double. This leaves us finally at 3-6 euros the hour per shredder, black since nobody can effort legal and real prices 🙂

I guess we have to work harder and faster just to make this ‘sustainable’, right ?
have a nice one,

17/07/2019 at 16:51

Hey community

@rbagg066, yes it will be the next download kit.

We work on it, like you can see 🙂

For assembly it, with all the part, take around 2 hours without the frame and hopper.
We will start the test the 29 July.

12/07/2019 at 22:07

Good points, @s2019; thanks. Indeed, we need a more complete guide on PET.. I’ve managed to find a few more DIY and PP shredder variants. In particular, I’ve found a more promising v3.1 candidate, @weedo and he seems to work on a double shaft shredder as well but I have no data on it, yet. Eventually we order just one from him, just to see how it goes 🙂 However; would be interesting to know how many people need a shredder that big. From our side, we don’t know many and I hope we can scale the v4 design down, making it also easier to add the mentioned grinder add-on for PET print.

05/07/2019 at 21:35

@pex12 , thanks. That’s a great start at a product description. I guess what I was hoping for is the requirements list that is being used to go from the V3 design to V4. The shredder is a supporting piece of hardware that in general does not produce an end product (though it is amazing how many people want to build it first). The shredder requirements come from the other machines and the business plan. With several years of use, there should be an understanding of what the other machines need.

Flake size: I’ve only used a version of the injection machine. For me, flake size has the following trade space. To create monochromatic parts, I often use the largest strips that will fit into the mouth of the tube, going smaller as the compaction process fills the tube. More recently, I used smaller flake size to create more interesting color patterns in the finished part. As I go smaller, I transition from manual feed (needle nose pliers) to using a small hopper. There may be other differences between flake size such as time to melt and time to compact out air bubbles, but I have not captured these. Perhaps this has been evaluated. Given all that, flake size of a couple of square cm is probably the smallest I need. For the compression machine, flake size, in general is driven by color patterns and the ability to remove air during compression. The PP team has done a lot of work on the compression machines. Hopefully they can publish some conclusions on flake size  in the compression machine. The extruder machine is the only one that appears to need a certain flake size to feed properly (probably depends on whether a wood auger or compression screw is used). Again, the past PP work should be able to set a requirement here, Though Paul’s work in the Maldives, feeding rope was interesting.

Materials and thickness: Do you need to worry about shredding PET if you don’t have a recycling process for it? Are you willing to flatten bottles and perhaps cut off the necks for separate processing? What thickness flat HDPE, PP, etc. does the shredder need to pass without jamming?

Throughput: in a small work space, with only one of each machine, there is quite a bit of time spent waiting for plastic to melt and cool down. How fast does the shredder need to be to effectively use that time?

There rest of the parameters (blade width, cutting diameter, tooth profile, shaft speed, shaft torque, etc.) are just trade space to get to a solution.  For example, if you are willing to flatten the feed material then a smaller cutting diameter can allow wider teeth or less torque or…

It would be very informative to see how the V4 effort worked through these (quantitatively) to get to the sizing and design shown above

05/07/2019 at 19:51

@s2019, I think i placed a link to the only data we have about in the v3 shredder’s resource section, although the data seems to have little noise. And as far I recon, they are still fighting with flake size, to a degree that comparison isn’t exactly possibly, yet.

05/07/2019 at 19:18

It would be great if the PP team picked some shredder performance benchmarks for comparing the various V3.x and V4 designs. Examples might be “what does it take to jam” 2L coke bottle? HDPE laundry bottle? What thickness PP sheet. Throughput would be good to know as well.

27/06/2019 at 22:50

looks promising; congrats. the recent builds of MorrenTrading use 2 motors (classy) to run such thing. Evtl. they share some details with you. I am still convinced that it’s impossible to get flakes size down whilst keeping an efficient low-power/spec -design; thus the mentioned ‘post-processing’ grinder module (at ~700RPM, 3 classic blades mounted on hexbar)  which only has one challenge : share drive power, via belts or gears. The very extra unit can be done for a fraction, as add-on as said; also enabling PET print right away as well better results for injection & extrusion.

31/05/2019 at 18:40

@sacrys, there all the issues we’d like to address, as best as possible without getting too much out of the window.

10/05/2019 at 01:43

confirmed: we make a grinder v3 shredder addon for getting PET grinded to dust. Only problem is the shaft length having enough space for a sprocket driving the grinder underneath. The printer itself is out of beta and we hope we have both in the bazar by June. Would be great to know the drawing, details of v4 so that the story ‘3D printing meets PP’ becomes even more reality sometime soon. thx!

08/05/2019 at 00:00

looks great! congrats. just some notes building this easier:
– if you can make the plates stick out by 2-3-4 cm around the chamber, it could already provide the mounts for the hopper which you can plug right on, with holes so all it takes are threads (M6 – M8), assuming the plates are at least 5mm thick
– please if possible, don’t make holes bigger than 35mm, most cone step drills stop there
– more on shaft holes on the side plates, we use sleeves for v3, not only to compensate errors and pre-load blades but also to have it easier to align the shaft during assembly, plus it provides a safety measure due it’s acting as rest as well
– not knowing the thickness but if possible, please drop the sink holes to montage stuff from inside (as v3); i’d prefer to bolt from outside, just to use any bolts (we tend to use more and more hardened ACME rods and make bolts ourself, way cheaper after all) possible. the other reason is that you can unlock those bolts without dis-assembling the whole thing before.
– the flanges are great but I’d prefer to deal with mounting myself in various scenarios, no biggy otherwise

overall great design, it seems to prevent mis-alignment/skewing (in theory 😉 and as always, i can be wrong 😉

@lagrenouille, not much, it’s made for PET bottles, you get one into it, it takes 2 passes to get it to dust, each pass ~1-2 minutes. 1480RPM at 1:50 on 0.75KW single phase. gearbox seems getting a warm easily but it was a pretty cheap one though. it’s a desktop shredder after all; a pretty good one, for whopping 4k but with CE.

do you guys have already spotted an european/alibaba supply for the blades ?

06/05/2019 at 14:38

Thank you very much for these pictures, it is very interesting !
Did you manage to have an idea on the qty you could shred by hours (roughly) ?

04/05/2019 at 22:35

here the shredding stage

04/05/2019 at 22:32

hey, so i had the 3devo (4k before VAT),
– grinds PET down to printable dust, in 2 passes (one reload after sieve)
– simple design after all, the side plates for the gears may provide enough space for such addon, or 2 .. as can you see the worm drive enables to rotate the force

02/05/2019 at 22:49

nice, thanks for sharing. i think its a no brainer, please say good bye just to single shaft, I am more worried about speed reduction, VFD, input power, maintenance. Please have look at the 3devo design, there is a second stage which grinds the flakes down to dust (printable). I have their grinder on my desk this weekend and let you know this could be an add-on 🙂

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