V4 Shredder Single Axis – [INDEX+BLOG]
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:
So here the Development Blog starts:
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?
I was told that here is good to share this design I’ve been working on as a side project.
The concept is a higher volume shredder that is relatively straightforward to make, with a built in chopper to reduce particle size. It’s probably 60-70% mature as a design and there are still a number of small things here and there that need to be ironed out. It currently does not have safety covers, a hopper or electrics. All the bearings, gears and motor are off the shelf metric.
The general idea is that the shredding section takes the plastic and reduces it to ribbons, then the choppers break it down into smaller parts. Could change it to two shredder sections though.
Attached is an image or two (3D rendered, this hasn’t been built yet) to show what is looks like. Let me know your feedback. I’m happy to share CAD files if you like, this is intended to be opensource. Also happy to assist development of it.
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.
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.
@btmetz shared some photos of a high rotating shredder. we build one pretty similar – just smaller. This shredder is working great… even with a power of an bicycle! We have 4 rotating blades and 2 fixed on the casing. The blades are out of hardened steel. We focused on that design because it’s working more like the industrial standard, which is high speed (about 1100rpm). It doesn’t need that much power. Successfully we tested a motor with 0,3kW/230V and a 28″ bicycle.
We doesn’t made an exact comparison test, but we think that this design is working more efficient than the current pp shredder. Another good benefit is, that the plastic isn’t that much electrified. This was on of the main problems we struggled with the current pp shredder.
At the moment we try to simplify our construciton, especially the axle.
I’ve started a topic in the forum, but it’s been a few weeks since I posted something. But there will be a video in the next few months about the building time and the cad files are also nearly finished…
Update: Proof of Concept – Shredder with Blade Inserts
Hey together – here is my current build of the next shredder version.
1.) The User feeds the plastic into a hopper (not displayed here), from where it falls down.
2.) A pusher feeds the material towards the single shaft with inserted blades.
There can be different types of pushers (manual-direct, manual-spindle, electric-spindle, pneumatic, hydraulic) depending on available resources and performance requirements.
3.) The plastic is squeezed between the pusher and the shredder blade and gets shredded downwards. The short blades and the closed cylinder enable the material to reposition itself during the shredding process, rather than getting stuck between the blades.
The blades can be exchanged easily and used from four different sides or resharpened when necessary. The final geometry might change to triangular blades (to set up the distance between static and rotating blade evenly) in a later step.
I you look at the Weima video 0:06 it appears to be using carbide inserts (such as used for lathe tooling) for the teeth. This would allow using a cheaper softer material for the bulk of the cutter and you can just replace (or rotate) the inserts when necessary.
I would recommend a dual shaft approach though, they seem to grab material and feed it through much faster. Also as you can make the cutters half the diameter to cover the same shredding area, you need less torque = less power. My dual shaft shredder is only 1/2Hp (375watts) and it rarely jams unless I really push it.
I also implemented an auto jam detect/reverse/restart feature, quite easily done with a microcontroller and an encoder on the shaft. What you can’t see on the video is that it will try several times to clear a jam (almost always works first time) but if it can’t it will turn off the machine.
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.
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.
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.
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.
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
Hey hey together,
has been a while now and want to give a short update on the shredder built.
We got all the parts prepared for assembly and welded the frame for the shredder as well as the shredding unit. Still waiting for some nuts and bolts to test the system. The shaft and reducer were machined, and we started to build up the electronic control system.
Would be awesome if someone with experience could check my electric circuit diagram at the end of this post.
Small Upgrade: Parts arrived
The parts came just before christmas, now some smaller bits and pieces are purchased.
The Cutters were a bit challanging to layout for lasercutting, but turned out quite nicely. However the clamps were too small, so they bent during cutting and everything got burned.
We will go for the easiest replicable version first and add another blade type later for readymade inserts or “professional made” blades.
Parts are cleaned from lasercutting and next is to weld everything together, build a frame for testing and set up the control box. The goal is to get the unit ready for the first tests in the end of next week.
Will keep you updated about the process 😉
@gcadou I have been using a kitchen blender and was thinking of scaling it up with an angle grinder as they are easier to get than an electric mower. It seems like the cheap and easy build. The blender blade design is needed to keep the plastic mixing.
I was also looking at buying a plastic shredder from aliexpress but I can’t afford the $2000+nzd and the 2nd hand market in New Zealand for these is empty.
The CNC cost of the precious plastic is also beyond my budget, so have been looking at alternatives for that style of machine. I was thinking of something like these milling heads at around $20 each might do, if a number are combined into one shaft. Or a Woodworking Finger Joint Shaper Cutter <= which could cut its own key(?- the grooved slots that the blades pass through and the plastic doesn’t).
So many options, I might start with the angle grinder blender because it’s easy even if it requires more operating time in loading and unloading the bucket.
@btmetz I think you might be talking about my friend Recycle Michael of WasteBusters and I turning his old electric lawnmower upside down and screwing a metal trash barrel to the top? Worked decently well one we changed out the single flat blade for some flimsy sheet metal ones we were able to bend up. We did a cross of the two sets of bent blades and screwed them on opposite one more bent up and the there down like you would see in a normal blender. It worked pretty well for blowing apart milk jugs when we tried it. We quickly moved on to the next thing. I’ve been meaning to do an instructable…still do…
some instragram videos below
Love + Trash,
more pictures here.
As you can see the blades are only leaf spring ground on a angle grinder.
I was discussing with a engineer the other day about shredders and the high speed unit I posted pictures of. We was thinking that it could be made with off the shelf parts (no cnc) pretty easily and instead of using expensive tool steel blades, one could use leaf springs sharpened with a angle grinder.
We already saw one unit built this way here in the Philippines powered by a small diesel engine.
remember the goal of this project is that it can be built in the third world. The extensive CNC machining isnt going to fly in the third world.
Hey thanks for your well-known reply, lets try to answer your questions 🙂
a) Indeed that was my first idea also. It’s still high in the list for the next iteration. I found out now, that there is a standard over different suppliers for those carbide inserts.
The question in the end is for which price we can buy them and how this will influence the machine price. I quoted yesterday the price for the teehts of this proof of concept. And right now one insert is around 0,30€ right now. The readymade inserts i found are in the area of 1-2€. Of course they are heat treated, sharpened, and professionally made. So its still on my mind but we have to consider also the worldwide availability of those and the price for ~150 Inserts.
I consider also to outsource it to a professional toolmaker and order from there in quantities of 10k+ to lower the price. But this would be also a major change of operation overall and is not discussed jet.
b) An interesting method! I have seen it on bigger shredders as well. Propably it can suit certain applications very well, e.g. if you have industrial waste and you know which size your parts have you feed in there.
c) Acutally i did not considered as a problem for now. For now the goal was to get up a running proof of concept as fast as possible, without spending to much time in optimizing the design for manufacturing, though the final shredder will be much different (bigger).
But i heard also from someone in South Africa, that he had big troubles to source the hex-bar.
A round axle with a/multiple keyway(s) might work as well, however you just shift the machining from a lathe to a mill.
From an engineering standpoint i assume its the best “solution” is to use a hex shaft, but I totally agree with you that a squared shaft might be a good alternative. I put this topic into the next revision research =)
Thank you very much for your input
Highly appreciate it!
Standardization can be your friend! Three questions:
a) I noticed your ‘hardened’ teeth are an hourglass shape, so I assume your thinking of getting four sharp sides out of that tooth before you have to replace it with a new one? Great idea, but why not use standard carbide inserts? Finding someone to cut, then harden, those hourglass teeth is going to be frustrating for a lot of people.
b) The linear actuator is an interesting idea, are you referencing the auger feeder design used in a production granulators? if you haven’t seen them, you should search it. Feeding material in, is a proven industrial method. Bravo on that direction and good luck in keeping that simple and consistent. I look forward to that development!
c) Why is a hex bar still being used? A standard round axle with a keyway is not strong enough? That hex bar is strong, but requires machining to mate with a bearing or pulley. Machining in general – is a huge barrier to entry. Just sayin’…even a square bar would be more readily available to more people.
Nice to see thoughts from other people on this machine! Thanks for the update!
to be honest in my opinion there is only one solution regarding these problems.
To be independent of the shape and rigidity of the waste input we need a shredding unit with different stages.
To safe money by using only one drive you will need a gear (belt or pinion type).
This will be the only solution to reach a maximum throughput in the same time.
What do you think?
(For some reason the video doesn’t start in the right place, skip forward to 3:15)
Thank you, much clearer
friedrich – Material selection is key here, 304 is by far too soft. For the cutting teeth, have you looked into taking a commonly available grade of steel that can be hardened, low carbon steel (AISI 1018) or alloy steel (AISI 4130) for instance, and heat treating the cutting edge by quenching after localised heating with a flame torch? Another method to get a hard wearing tip is hardfacing using a welding setup (MMA is cheap). Saw these comments made by bastelmike, servant74, micro and tatheta elsewhere on the forum. Also, forming the teeth before heat treatment to a chisel point, as I saw justinc mention in another thread, will help with wear. This can be done with a simple file.
I can help you out here if you want, got a fair bit of materials selection knowledge, especially with metals.
brettc – If you go along the route of the milling cutters look into ‘gang milling’, and cutters associated with that, they can be set up on a single axle with or without spacers. Depending where you are you might find a machine shop that just has them ready to give away / throw out / sell cheap, it is an older method from before NC.
You’ve got me thinking, could get 5mm gang mill cutters and replace the cutters in a Precious Plastic shredder, might help with the wear..
Ohh wow, thats a nice one!
I would really like to have a look at your CAD Files, will also share mine below. Could you send yours to fr[email protected] – thanks a lot 🙂
So you use two motors in your design? Looks quite narrow space-wise^^
I like the idea of a belt drive to add some additional spinning mass to the shredder blade axis. Especially the opening drawers on the side seem like a useful addition to a shredder, so maintanence and inspection is easier this way.
I think the main issue is, as earlier mentioned, that the process of shredding is not a predictable one – you throw things into our shredder, but you never know if it will be shredded by itself or if you have to push it or even stop it and reorient the piece.
After this stage I will have a closer look by testing in multi-stage shredders and try to give an evaluation for it. Not sure if it makes sense, because its always hard to define a testing-pattern, but let’s see.
Its true, there is no CNC machining in some places, so i try to stick to already proofed technologies like laser-cutting. Making a high end Shredder Shaft based on 5 Axis CNCing would be a easy one^^
But also in prototyping and testing you want to go as fast as possible – optimizing for rebuild is another step i think.
Here are the CAD Files of our new Proof of Concept Prototype. Feel free to download and comment on them.
Please don’t redistribute anywhere else online, to make sure its clear that they are under development and not final in any manner.
Greetings – Friedrich
What if we are looking at the v3 shredder wrong? Aside from tooth profile.
In other projects I have done in the past, I used armor plate to make blades for hammer mills, high end knives, and hatchets.
What if we just waterjet the cut blades from armor plate and maybe change the teeth of the shredder to 4 or even 5?
I have used Ar500 and Hardox in the past. Both pretty much similar. They would work better than tool steel as they are pre tempered and the toughness and hardness is already proven.
Uh, vergass ich, can Ich auch ein bisschen Deutch sprechen.
gravity is always your friend! maybe try rotating the linear actuator/pusher plane 90 degrees so it’s pushing the plastic down into the blades. the hopper can still come in around the sides of the actuator.
most shredded plastic is cleaned with more cheaper lye, not bleach… both are chemical base (not acid).
I used a more industrial shredder last week and it had a similar blade arrangement as this.
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