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02/09/2019 at 17:42

For a composite of wood and plastic, if you are using wood fibers with plastic, it should work a bit like fiberglass, I know Futures developp something like that (real info on the plastic is hard to find though !!!). But if you inject plastic around wood for example, then your product will be absolutly non-recyclable, as non separable. While fiber of wood/glass/carbon mixed inside a specific plastic, can still be recycle by itself, even mixed again with this plastic without fiber, as they are no degrading the properties of thje plastic.

I am working on a new mold with FCS II system.

I also tried to incease the preasure with a air jack modified injection machine, compacity is better, but still have to be better.

For the mixing of plastic and fiber, I am sure I have some bond, but maybe not 100%. I try to document myself on it, but accesible data on how to bond fiberglass and thermoplastic are hard to find also.

Next test will be this week-end, I found some fishing net, that should be polyamide, theorically very tough. Let’s see !

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) ?

24/04/2019 at 12:42

No worries, I just wanted to say that yes, this shredder will be bigger and in another price range for sure, as we want to have this alternative. Also this will be a parallele development with the single shaft, only one will probably be released at the end.

Therefore I am and will be very thankfull for all your inputs to make it easier to built, cheaper, more efficient… if you would like to of course.

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 15:51

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

Here some additional pictures 😉

18/03/2019 at 13:58

@pporg I think I added the .f3d file, it doesn’t work ?

I will modify it, it seams that the 36mm hex bar is an easy one to get a bit everywhere around the world. Motor side is very depending on what you find.

A real motor alignment is something close to impossible if you don’t have a kick ass milling machine where you can put the entire frame on it, so yes, the tricky part is to have a misalignment tolerant coupling.

I would be interested to see you DIY aluminium jaw coupler.

14/03/2019 at 18:11

Finally made the 3d for this coupling, I share the link for fusion 360 and .step file under.

It is made for a 25mm axis in shredder side and 35mm in motor side. I will try to modify it for a parametric system soon, but I have to learn how to do it.

22/02/2019 at 11:46

@s2019 I have more expertise into material sciences and welding, so hydraulics is quiet new to me. I worked on boiler building for a few years, so I know the pressure danger, pressure gauge and safety valve, even if in that case, I don’t really know where to place them. I’ll dive into that, there is probably a way to monitor hydraulic pressure or a way to relate air and hydraulic pressure.

I didn’t thought about a load cell, that is very smart, even if it might be very pricy as you said I guess.

21/02/2019 at 12:18

@s2019 I am currently building a new injection machine for myself, based on air driven hydraulic press ! I shall have all materials befor this week-end, the building should start friday evening.

I have a question, that you might have the aswer : I am afraid of the really high pressure that can be put in the mould, with no real control (you don’t really feel it once you inject the air). How would you control the pressure during injection ?

15/02/2019 at 09:06

@s2019, thanks for your inputs !

I have a 1mm fillet at the base, so no sharp cut, but maybe not flared enough. I will have a big review on the drawings.

I made some in workshop load test before going into water, but my main mistake was not breaking any commercial fins to get a reference value… I am still very reluctant to this idea, but I guess I have to go through it !

I also wanted to test the flexibility of the fins, and the feeling of it, even if very doubtful about the overall resistance. This part is validated still, they are nice to ride.

Generally comercial fins are made with thermoset resin, I found only a few out of thermoplastic. Maybe the main point is that I want to built an impossible product, but I am very stubborn !

13/02/2019 at 18:22

I managed to make the first testing, and… it didn’t end well !

If during the whole session the fins were super nice to surf, no speed lost at all on turns, on the last wave, they sudently desapear ! The wave was slightly bigger, but still : not strong enough at all !

I tested then on shore other fins, injected with only PP, and they are even weaker. Who else already tested fins into water ?

Of course these two small legs are a big weak point, but it comes from the most comonly used plugs (FCS).

So two orientation now :
– Working on inserts inside legs
– Working on a better injection machine, with more pressure (bubbles in the middles of these fins).

07/02/2019 at 22:19

That looks nice !

What size is the pipe / max volume of plastic ? Wouldn’t it be more compact if the rack & pignon were smaller to go inside the barrel and then having a smaller round bar (but then maybe not strong enough) ?

It looks a bit like Taller Esferica one, did you do it in collaboration with them ?

07/02/2019 at 18:04


We went recently on a laboratory to be able to do some tensile test on ropes. Result are very promising as you can see on curves obtained, we have a very classical elastic material comportment.

Result can be summarized that way :
– Each 1mm strip included in a rope can hold 2,5kg, before rope definitive deformation, and at least 2 time this weight before break (sliping out of the machine before breaking) : 15kg for a 6 strip rope, 30 for a 12 strips rope, 45kg for a 18 strip rope…
– Ropes are approximatively half resistant compare to a same linear weight industrial twisted polyester rope, even if diameter of PET rope is bigger. For 11g/m : PET is 5,5mm diameter for 3,5 for a twisted polyester rope
– Elasticity is very important : 10% before definitive deformation and more than 100% before break. In comparison, a PET straight bar can hold max 36% deformation before breaking, and a twisted polyester rope break aver 20% deformation

07/02/2019 at 18:02


Then this cutter will be integrated in a small production line to be able to process it efficiently. The bench is though to be built completely as the fist time, and complete step by step by adding the tools depending on what is wanted.

It will contain 3 modules :
– Pre-cut bottle bottom to increase production
– Strip cutting with mechanised pulling and storing
– Strip calibration to a wire with mechanised pulling and storing

This last step is also one on which I spent quiet a lot of time, but application can be endless. By heating an aluminium piece with calibrated hole, you can use the thermoreaction of the PET to give a round section of the strip by pulling it through. No fusion is involved, so PET is still very easy to process.

This small round wire can be then used as fishing wire, sowing wire or maybe even 3d printer wire with a very easy production process (It have to be tested, but I am waiting my 1,75 calibrated hole !). This would still be limited by the strip length, but you can obtain 25m of 2mm strip out of a 1,5L Coca Cola bottle 😉

07/02/2019 at 17:58


Difficulties :
– Bearings sharpening
– 0,5mm precision for bearing and guide position holes
– Welding and threading needed
– 0,5mm precision cut for spacers

Machine needed :
– Grinder with cutting disk
– Table grinder
– Drill press
– Welding machine
– Measuring and marking
– Thread makers

Steps :
– Cut a 80*100*>4mm plate then drill and thread it as indicated on the drawing (see picture),
– Cut 3*40mm M8 thread bar, then make a cut in one of them (~7mm deep, ~1-2mm wide),
– Cut 2 spacer in a pipe with 8mm internal diameter, one 10mm and one 17mm,
– Cut a 400mm 4mm rod,
– Sharpen two skateboard bearings by putting them on an axis (M8 bolt) and using a table grinder (see picture),
– Install the two M8 thread bar without the cut on the front holes, and the 4mm rod on the 4mm hole, they should brush the bottom surface,
– Weld them in space from the bottom surface, then grind it flat again,
– Install the third thread on the last M8 hole, the cut shall be on top,
– Install a spacer, a bearing and a nut (in this order) on each front M8, start by the 10mm spacer, that shall be on the 4mm axis side

Cutting steps :
– Cut bottle bottom in two steps
– One sloppy to remove the bottom
– One fine to make it flat and smooth
– Without any pre-cut, place the bottle on the vertical axis
– Place the cut edge in the guide and slide it between the bearings
– If needed, slightly pull down the bottle doing so
– Pull the created strip, the speed will depend on the bottle regularity
– Once 2/3 of the bottle cut, put a weight on top

Tricks :
The cut thread is the guide, you adjust the height by screwing or unscrewing it, every half turn will move it by ~0,5mm
Adjust the axis (4mm rod) depending on bottle diameter, it have to be slightly bend on the back and on the external
Pulling speed is the key for regular strip, play with it 😉

07/02/2019 at 17:56

Sorry, long time not posting here, but it doesn’t mean I didn’t work on it !

I actually spend quiet a lot of time figuring out a reliable method to make strip and wire out of PET, and then design a built a first prototype. This have to be seen as a production line to obtain a base material, this material having to be used in various application, still to be experimented, afterwards In comparison, this would be the shredder equivalent for PET bottle, that you can then process for weaving, rope making, attachment…

So the first step was to obtain a reliable cutter. Previous version was built with a cutter blade, the big inconvenience was the unsharpening of the blade : the cutting always occurring on the same spot, the sharp edge disappeared very fast. So we switch to a system that actually shear the bottle instead of cutting it, by pulling it between two overlaid bearings. I will call that a ‘not to difficult to built system’ but once taken the time need to make it, it is super reliable and versatile.

06/02/2019 at 11:34

As for making my fins, I need a good mix of the plastic, I really like the idea of having a screw that would pre-mix and bring the plastic directly into the injection chamber.

I might consider making something similar, but with less automation probably (I am not really confortable building automation system). I have a question : how the “extrusion” barrel is connected to the injection chamber ?

04/02/2019 at 17:43

Thanks for compliment about quality, that’s what I try to do, but it is quiet hard to get something which is not only nice looking but on what you can also rely on. Hopefully, it should happend soon 😉

I agree with you on books, you need to document first. And you need to try also, as most of the documentation comes for industrial machine, which doesn’t necessary apply for far weaker precious plastic ones ! I will take time on my next post to explain what on my mould I took from industrial mould making design, and what I change to make it applicable to PP.

Thanks for the links, it seams to be proper books ! Did you read them though ? Because by the title, I am note sure they really apply here, it seams to get more detail on extrusion than injection and the composite seams to be more resin based than thermoplastic based ? I said above I don’t think book explaining industrial process fully apply, they might be a starting point, but you need to move from that and I think stjepanb need more feedbacks on which technics you can take from these books to apply on PP.

25/01/2019 at 13:54

As it is a comment I regularly have, here is my point of view on the subject :
Fins are not a single use product or assimilate, you barely broke them, and if you do, it is generally in water, which means that regarless of the way you built it, it is a waste, so it is best to build them as strong as possible.
Currently, they are made that way, strong, but out of new petroleum based material. As the best waste is the one that doesn’t exist, the best solution would be to stop surfing, but you can ask any surfer : I’d rather stop everything else in my life than surfing 🙂 !
So I am in an in between with a fin that would still be 100% recycled at least, wtih PP wherever you can find it, and fiberglass out of lost cut from surf making industry.

Also the fact that mixing PP with fiberglass makes it non-recyclable anymore is quiet false. I can still shred it again and inject them back in another fin.
But you are right that it creates another plastic category, and it is hard to know how many fiberglass is inside if you want to make another product where you plan your resistance on this fiberglass. Howerver it never degrade the plastic as it would be if you mix different plastic or wood chips for example. So I could also just shred it and inject it in another PP product, mixed with full PP chips, it would still work. I will lost quickly the count of fiberglass inside, but as long as I don’t reckon on them, it will never make a weaker product than a full PP one.

But of course, it is only my point of view, open to discussion.

And to answer your question @stjepanb, I learn plastic injection during my engineering degree (material sciences), even if I focused more on metal work since, I still remenber some stuff or have acces to my basic courses, but unfortunatly, I don’t really have good book to share.

24/01/2019 at 12:44


I didn’t properly checked, but it looks like there is no immediate damage visible. It might cause a premature wear of the blade I guess, which imply more maintenance or differente steel type.

22/01/2019 at 19:02

There was some great improvements these two weeks. I figure out a better method to mix PP and fiber glass together :
1- Shred pp
2- Shred fiber glass (with scisor before finding a better solution) – average lengh around 10mm

3- Mix it together

4- Extrude this mix

5- Shred it again

6- Inject this new mix !

It doesn’t cause any trouble during extrusion or injection and is injectable as standard PP. The resuklt is clearly more rigid (25 % fiber ratio in mass).

While it is still not to my taste in term of rigidity, I feel that it is going somewhere.

Then I went for second test with carbon fiber pre-treated for injection with thermoplastic that I bought on internet. Average lenght is 0,1mm.

I tried both mixing it directly in the injection barrel and with an extrusion pre-mixing as I did for fiberglass. Both time the ratio was 25 % fiber in mass.

Conclusion :

– The Precious Plastic injection machine doesn’t allow a proper miw of the plastic and the fiber, an extrusion pre-mix seams to ne mandatory.

– With fiber 100 times small than fiber glass, I get more or less the same properties with carbon fiber. This can be explained by the change of material, but more likely also by a specific treatment that was applied on these fiber to make them compatible with thermoplastic.

– Using carbon fiber makes the final product black whatever the shreded PP is initially. Even if the black is quiet nice while pre-mixed (mat apsect), I feel that we loose some cool properties of Precious Plastic machines.

I will then concentrate my research in finding the right fiberglass ratio and a proper treatment to allow a proper bond between the fibers and the thermoplastic matrix.

1st picture : some graphic of the pre-mix process

2nd picture : last fins injected (PP + GF direct injection / PP + GF pre-mix / PP + CF direct injection / PP + CF pre-mix)

3rd picture : flex comparison with a approximativly similar load

07/01/2019 at 13:00

Some new testing during christmas vacation !

PS :
– 270, 280 & 300°C : seems to inject quiet well even at 270°C but need more speed than PP tho.
– The bright sound of PS make the fins feel cheaper will in hand
– Doesn’t really change the flexibility, still far too flex

– 280°C : not fully injected, not brittle
– 290 & 300°C : not fully injected, super brittle

PP + fiber glass :
– This time shredded fiber glass mixed with PP inside the injection barrel
– Very well injected at 280°C
– No big difference observed yet

Conclusion :
– Abandon of PS : no big difference observed on the flex, the plastic is less pleasant to work with, and the final product kind of feel more crappy
– ABS seams very promissing, but Precious Plastic machine doesn’t seems to be able to inject it.
– There is probably something to do with PP + FG, but I need a better mixing, and also a better connection between the fiber and the PP matrice.

To follow :
1 – Pre-mix PP and FG with an extrusion machine
2- If it doesn’t work, buit a better injection machine with a crank
3- If still not OK, increase the thickness of the fin

23/12/2018 at 16:25

I started fine tuning of the injection to find the right paramteres, some parts of the fins are very thin and then tricky to inject.

First trial on top of the picture with HDPE :
– 200°C for the rose one : absolutly not fully injected + cold cut on the jonction point.
– 270°C for the two yellows : fully injected but still this cold cut

Then I went for PP which I know easier :
– 240°C, 260°C, 270°C for the four blue and then the 2 first dark green : no cold cut at all, but not really fully injected (few miss on the bottom left)
– 280°C for the two other dark green : still no cold cut and perfectly injected

First conclusion :
– HDPE doesn’t have the same fluidity and displacement inside the mold, it look more like a front of cold plastic move inside, then doesn’t melt when it meet the second cold front
– PP gives the impression it rolls on the mold, so both front are still fused when meeting
– 280°C seems to give the right fluidity on PP to be able to go everywhere in the mold (I don’t want to heat the mold for the lost of energy it would imply).

@bbreve I think it is actually too flexible with only PP, so I then went to try fibre glass addition (not recyclable anymore though) the only trial done was to pinch a piece of fibre glass between the two mold part and inject around. It seems to work quiet well but is quit difficult to place properly. Also the fibre is in the worst position to be usuful (fins work under flexion, where the middle wil not receive any effort). So next research will be : PP + fiber glass, PS, ABS and PC.

23/12/2018 at 15:59

I was also thinking about injecting the plastic around the blade, but I somehow find it less esthetical. I didn’t think about multiple mold though, that would be a crazy idea, I might rethink it 🙂

21/12/2018 at 18:00

I recently find my definitive shape, then cut the central par of the mould out of stainless steel. It works far better than with plywood, and nothing get stuck on it.

I am currently preparing a detailed documentation, but you can find under some picture to understand how the mould is built :

11/11/2018 at 15:33

As I have some questions from time to time about what we would use the rope for. Basically everything you would use a normal rope !

Here some application already under testing : hanging clothes, lacet, bike luggage rack attachment, dog leash.

Also, we can use the strip directly to make various construction. Here an example on attaching a paddle on a wood handle. You can use the retraction propertie of PET to normally knot anything with a strip then heat it to really tight the attachment.

More example wil follow depending on our moment inspiration or needs. Some ideas that come to me immediatly :
– Stool woven seat
– Swing
– Boat mooring…
Do not hesitate to give us ideas !!

08/11/2018 at 12:45

A little bit more information on how the ropes are done.

First GIF :
Frist of all you must obtain some strip out of a PET bottle. As said on the post above, the thiner the strip is the better outcome you will get. Also using ungrooved bottle simplify the process. Out current cutting maching is a cutter blade placed on top of a calibrated cut on a metal beam. The depth cut shall be the strip width you want to obtain, and the cut shall be as thin as possible for the strip not to tilt during cutting. The bottle is maintained to the right angle with a metal guide.
We added a system that allow us to spool the strip autimatically in order to save time.
Further improvment have to be done on this machine :
– Better rigidity
– Easier and faster spool set up
– Better guiding system (this one is difficult to set up)
– Add a system to transform the flat strip into round filament
– Add a system for bottle preparation before strip cutting

Second and third GIF :
Then you can process a rope. Still with a drilling machine and a belt, three pins are rotating together. Then on the other side, the tention is maintained with a weight, but with free rotation possibility. You have to maintain your yarns separated until you get a satifying torsion in all yarns. Then the yarns are automatically turning arround themself making the rope.
You can vary the rope size by adding more filament, by using pre-made small rope to obtain a bigger one etc… Rope lenght is theorically unlimited as both system side are independent from each other.
Further improvement will also be done on this machine :
– Independant set up (instead of using a table)
– More versatility (more possibility in number of yarn & strand)
– Possibility to count rotation number (important rope caracterisation number : higher rotation number means denser rope, and denser rope means more tensilte resistant rope, but up to a certain limit, to dertermine for PET)

29/10/2018 at 23:41

Whoa @lukashatihatala ! Nice work !!

Can you share the 3d when finished, I might try to build a proper one in the current workshop !

23/10/2018 at 11:11

Hi guys ! Yann here, working with Kai on finding solution for PET bottle, and last week we worked more specifically on rope making.

First there is some parameters that are mandatory during the process :
– Keep equal tension in all fibers / yarns
– Equal rotation speed for all yarns
– Perfectly free rotation at the end of the rope
– Keep rotating all yarns while the strand start to appear but at lower speed
– Maintain reasonable pressure on the separator

Here are some parameters that have influences on the rope quality and that we had tested / will test :
– Bottle strip width and regularity
– Untouched strip or “pre-rotated” strip stabilised in this form with an air heater
– Flat bottle or grooved bottle (influence on regularity)
– Same bottle type or mixed bottle supply (influence on regularity)
– Fiber joining (knots, torsion…)
– Tension (at the end of the rope, by the rotation tour number…)
– Rope type : quantity of fibers per yarn, quantity of yarns per strand, quantity of strand per rope (currently making a 2 fibers per yard / 3 yarns per strand / single strand rope, a fiber is corresponding to one bottle strip).

Some conclusion have already been found :
– Pre-rotating and heating the strip makes it look smoother and gives it a better reaction to torsion : the strip resistance being more homogeneous.
– The smaller the strip are, the better the rope appearance and smoothness is.
– There is no need to pre-rotate small strip (up to 3mm), but it is mandatory for bigger one to maintain a good appearance and a proper torsion reaction during the making.
– It is also mandatory to pre-rotate irregular strips for the same torsion reaction (risk of breaking in weaker spot before obtaining the right torsion).
=> Therefore the best material for rope making would be strips as small as possible, supplied from the same ungrooved bottle type.

And eventually we will continue working on the following point :
– finding the best cutting method to obtain small and regulare strip + automatised process
– if possible this cutting method works also on disparate and grooved bottles
– finding a better connection method than knots
– when the process is mastered, experimenting on various fibers/yarns/strands quantity

16/09/2018 at 13:08

I improved a bit the system : now working with the injection machine !

It is a very simple mould :
– Top : stainless bended plate (in width direction) with standard injection nozzle
– Middle : 5mm plywood cut to the desired shape
– Bottom : same stainless plate than for top
– Lots of bolts to keep it tight
– Size increased injection pipe : I went for a 1’1/4 pipe with internal diameter of 35mm. I did that to be able to melt 230-240g of plastic (final product is 190g). Standard 1′ pipe wouldn’t have been enough

Big improvement is for the stiffness of the product. The first ones with bended plates tend to regain their initial form if heated again (for example if left inside a car under the sun…)
Second one if for waste created, I am very close to the final form and only have to shape the rails, which is done with a knife above a box to reuse shaving.

There are available in one local surfshop, and soon on the bazar 😉

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