My shredder construction log


Just thought I would make a thread of my shredder construction.

After a weekend of fiddling, I managed to get the machine to an assembled state (please ignore the welding quality, I have just started to teach myself how to weld).

I will be spending this week/weekend tuning it so that it rotates smoothly.


With that set up you have the about the best gear ratio possible, but really it needs to be much higher. If you could swap the sprocket on the shredder shaft and the chain ring on the bicycle crank it would give you much more mechanical advantage, but would involve a bit of engineering. Your best option with least work is probably to get a mountain bike crank with 3 chain rings, run from the smallest chain ring on the crank to the large sprocket on the cassette, Put as large a sprocket on the shredder as you can (maybe the large chain ring from the crank) and then run to that from the smallest sprocket on the cassette. If you can get 4-5 turns of the pedals to one turn of the shredder that should be enough, but the more the better!

Also if you remove the freewheel from the cassette (or mount it with the original spindle) you can pedal backwards to clear jams and set the pedals in the optimum position to apply torque.

Hi ppboys,

it isn’t apparent in the video, but my motor is connected to a Start/Stop station that has a contactor and overload inside.  The whole thing was wired up and tuned by an electrical engineer so I am confident that he did it properly.



@simonm, we do the couplings most of time our self (needs CNC, lathe and a bigger shaft) and to avoid over – torque, there are various options too : VFDs have that often built-in (needs to be activated and tuned) and there a number of standard electrical components (shneider) which trigger at certain amperage.

Hi Facundo,

My initial plan after my coupler shattered was to get a much stronger one machined up.  But having thought about it for a few days I now don’t know if that is the best solution.  If I make the coupler too strong, and there is another jam, something else much more expensive to replace could break.

So I will be talking to a mechanical engineer about getting a new coupler built that has a shear pin.  Then if there is a large load put on the machine again the shear pin snaps rather than the coupler.

I will add photos to this thread once I have a new coupler built.



I think you can…but not yet built one.
Stay tuned…

Wanna come visit Panama and gift me your bike? I am in love with the idea of a powerless shredder.

Hello everyone, if you connect your peddles to a bike wheel,and use the area that the tire connected to as a pully to you shredder…One full spin of the wheel will turn the crank very fast.The blades may be singing…

@laluna, I don’t think so. There were quite some attempts to make a bike shredder and none of them looked convincing. Mechanical wise, it’s quite a challange to create enough torque. The most promising candidate is the one below. We’re still waiting to get details on this build.

Ok, here is my next update on my shredder construction log.

I eventually gave up on the pedal-powered design.  I am not saying that it is not possible to have a pedal-powered shredder, but for someone like me who has no mechanical experience I found it beyond my skill and ability.

So I have moved on the an electric motor driving my shredder.  I have done a bit of a video here –


My next step is to use a heat press to make plastic sheets and a CNC Router to mill the sheets into jewelry.  I will provide additional posts around that process as it goes.



That will depend on the thickness of your blades, primarily, relative to the scree/sieve you have installed.  If the blades are taking big “bites” that don’t pass through the screen on the first try, they’ll come around and get run through again.  It seems as though a big difference between the screen and the blades runs the risk that you spend a lot of time churning half-chewed bits of plastic until they happen to hit the blades right and fall through.

Hi everybody.
I just joined the community. I’m starting to desing my own shredder and a  question came to my mind:
@simonm: How many times does the plastic have to  be crushed to get the final size of the pellets? ( the size showed in precius plastic videos I mean)

Thanks a lot!!

Has anyone tried a “treadle” configuration like was used on an old stone grinding wheel?  Once you get the stone in motion, keeping it going requires pumping the pedal, but could allow a configuration where the shredder operator is also powering it.  (Something similar to a “Stairmaster” would seem like it could also work, but the mechanism for driving it with two independent chains is a bit more complex.)

Any up dates on this really interested in the bike shredder @lisali

Did ya build your injector @simonm?


we also built a pedal powered shredder very recently.

as is the video /construction from simonm, it is not very easy to get through the plastic with just pedal power. it cloggs sometimes. as the frame+shredder box and the bike are two separate items, conncetd with the chain only, everything moves, when something gets stuck. our gear ratio is about 1, so it might not be optimal also.

the fly wheel could be a possibilty.

Any suggestions/ideasa for us?

we are placed in Berlin.

sincerely yours, lisa

Hi @jacobroy-quebec, sorry for not replying earlier.

I will send you a photo of how the gear is attached to the shredder tonight when I get home from work.

Hi @katharinaelleke, no, I have not really improved on the design. The whole idea of this design was to provide a cheap shredder while I get the whole thing up and running. I am trying to build up the courage to do the injection mold next. Once I have that going and I am making items, I will see how they are accepted. If I am able to get some interested (and associated income) then I will be replacing the pedal-power with an electric motor.

@simonm, really like your construction!
Is the video your final version or did you continue working on it and managed to improve it?

literally just had the same idea after seeing a spin bike at the gym… (using a heavy flywheel) I think it’d really smooth out the shredding action – does it also add torque?

Hi @simonm

First of all, congratulation on your wonderfull build!

I wanted to know how you attached the gear to the shredder’s rod?
Mine is plain milled and I can’t figure out how to install a gear!

Thank you!