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The story behind the 'Bicycleshredder'

This topic contains 13 replies, has 6 voices, and was last updated by  Kunststoffschmiede 1 month ago.

Kunststoffschmiede kunststoffschmiede

The story behind the 'Bicycleshredder'

04/11/2018 at 16:32

Hey guys and girls!
During the summer the Kunststoffschmiede was requested to do workshops or presentations in Dresden, our hometown, but also in several other cities in Germany. That was a pleassure and we had lot of fun, but one thing that was really annoyingly was the transport of the machines. Especially the huge shredder, about 40-50 kilos, I guess. Another big disadvantage was the power source (380V/16A)….

So we decided to work on a new machine!

We shared our vision of a new shredder in our local network and asked people to participate designing and building a shredder. 4 people said: Yes I will! Thank you, and thanks to the germany ministry of environment, which financed this project! With Pascal, Paul and Carl from the Kunststoffschmiede team we were 7 persons. During august and september we began to make a plan and in october we built it.

In the following post’s we will share the story behind. But first of all some impressions;-)

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04/11/2018 at 23:38

It all started with an analysis about what does the machine have to do:
mobility -> has to be carried on a bike
human powered / independently from electricity -> we transport it with a bike so we also have to create the energy to shred plastic
lightweight, compact and solid -> not that easy:)
maximum safety priority and easy to use -> we work a lot with kids or youth groups. So everything has to be safe and simple to understand.
shred plastic efficient

Solving approaches of the main parts

Mobility. Here we considered 2 options:

1. One bike firmly connected with the shredding unit
– one single functional system
– super mobil, everthing is on the bike
– in case the bike is defective the shredder is not working
– heavy bike

2. Modular shredding unit you can connect to every bike
– the shredding unit without the bike is compact to store
– people can use their own bike to shred plastic
– some people are smaller some are bigger -> we are able to change the bike for differnt body sizes
– no process gurantee -> every bike is a litler bit different. We can’t be sure that ther shredder is working with ever bike.

We decided to make option 2 with restriction: Only 28″ bikes

This is one of the first sketches:

05/11/2018 at 05:25

Hello Kunststoffschmiede

Big up for the bike shredder!
What you did is amazing.

We also developed a shredder bike but we struggled keeping it both smooth and powerful.

As we are doing workshops with kids we prioritize a design that make it seamless and smooth to cut the  plastic we it makes it very slow.
What we did is to add lots of gear, to keep it powerful and we changed a bit the design of the blades.

The limits of the bike for us is that it can shred only small or soft pieces such as bottle caps. If we try bigger pieces what happened is that the chain jump out or the belt break.

Our shredder bike is easy to move around because it’s very stable but the blade box makes it very heavy.

We shipped the machines from Shanghai to Beijing several times and the bike never got any damages.

My question is how do you make the bike smooth to ride and have enough power to shred? Do you pre-shred the pieces?


05/11/2018 at 09:00

Hey @adelef
We made a completely different blade design and we are working with a high RPM and low torque. More or less it is exactly the opposite of the ‘normal’ precious pladtic shredder.

We precut the plastic in pieces that fit in our hopper. Until now we just have tested PP and i think the max. Thickness was about 2mm.

I will write a detailed post about the shredding unit this evening. With some pictures, drawings and facts…


05/11/2018 at 09:55

Great project! Would it makes sense to have some detachable weights on the wheel of the bike to turn it more into a flywheel when in shredder-mode?

05/11/2018 at 11:06

For the shredding unit we also have considered two variants.

1. The fast one (about 1100RPM / 180-250W)
– low torque fluctuation
– we have a working prototype
– special cutting knives and axe
– very fast -> maybe more dangerous than a slow one

2. The slow one (about 100RPM / ~2000W)
– we have a working shredding unit in our workspace (but with a big electric motor)
– less dangerous speed
– a lot of power / torque is necessary
– fluctuating torque -> not good for any drive source
– heavy -> a lot of lasercut parts

We comoared both variants with the proporties of a bicycle. It is possible for a person to get 200W out of a bike and with the right transmission we are able to reach a RPM over 1000. A power of about 2000W respectively a very high torque is more complex to realise on a bike.

With this comparison we decided to work on option 1. Furthermore we ththoug that it would be safer because to get the high torque for option 2 it is necessary to have a flywheel and imagine something gets stuck in the shredder and the machines stops to turn, but the energy is still there. So maybe the chain jump or the belt break like the people in Shanghai experienced with.

@siemenc i do not think that this is necessary. With normal waste we do not have any problems to shred it. It would make the machine heavy and more difficult to stop

The pictures show the principle of the shredding unit and our first protoype with an electric motor (230V/250W) in a case out of acrylicglas and aluminium.

04/02/2019 at 19:54

Nice work guys.. can’t believe I’m only finding this topic now. I like the simplification of parts. Fun to use too..

We’ve got a shredder here that functions the same as yours (same blade design + high rpm) but it creates a lot of dust and statically charged plastic that just sticks to everything. Do you have similar problems? Maybe its a matter of ours just being too big and fast 😕

04/02/2019 at 21:41

thanks @timslab!

the problems you mentioned are the major problems we have with our precious plastic shredder. with our “new” design we are a lot better.
a little bit of dust yes, but not that much. for all i know the big industrial ones are producing dust too. we focused on getting the shredder as much leakproof as we could. the hopper is crucial, furthermore it’s good for the safety;-)

statically charged. it’s like the dust. a little bit but not in comparison to our other model. we are using a metal box for the collection box, so maybe this beneficial to “discharge” the plastic.how fast rotates your shredder?


08/02/2019 at 17:50

I see @kunststoffschmiede, thanks for answering.

The one similar to yours runs at about 200 rpm, and is quite bulky. The blades are also set at a bit of an angle so each cut kind of shears the material. I’ll take some pics the next time i clean it out 🙂

15/03/2019 at 19:20

whooop, we’re finally ready to share with you all our drawings, files, etc…

here are the blueprints!

15/03/2019 at 19:28

and that’s the video!

15/03/2019 at 23:54

nice, i wanted to build a home trainer some time ago and yours seems perfect. any chance you re-arrange all that one can feed the hopper whilst cycling more easily ?

29/03/2019 at 12:23

Thats really cool! I’m really having problems to find out everything (without spending hundreds of euros) on the classic PP Shredder (as lots here) and also wanted an efficient and ecological system to power it so this is perfect!

Which kind of plastic did you manage to shred with it? Its HDPE an option with this method? Could you tell us which kind of plastic did you successfully shred and which thickness?

I really liked the hopper you’ve designed and extra security it gives as I also wanted to use it in an educational way. How much plastic do you manage to shred for hour? How little you have to pre-cut the plastic input? And what about the blades used? Which kind of maintenance you apply on them (resharping, substitution, how long do they last)?

I love the way you attached it to the bike but i think i would be nice to be able to put any bike available and just transport the machine. I don’t know if you kinda thought about this and what problems you faced (I can imagine that the variety of bicycles makes it quite hard to adapt)? Did you measure how loud it is while working?

Thanks a lot for sharing the whole design, awesome job guys!

31/03/2019 at 08:58


first of all, we found some errors in the files for the casing parts.
we will fix it and then we will upload it again. sorry!

mostly we shred pp. a few weeks ago i tested hdpe bottle caps. the thickness is up to 1,5 or 2mm i guess. at the moment we have no date about how much kg per hour. i think it’s a little bit more then the normal pp shredder produce.
We have to check how long they last. but you have enough material to resharp them 2-3 times.
mhm, we build the frame to put it on any 28″ bike. it’s not easy to find a design which fits to every bike, so we focused on 28″ because these are very common in europe.


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