Precious Plastics Builders Meetup


After a Precious Plastics Builders Meetup held at Gearbox Lite on 13th Aug., participants expressed interest in furthering the discussion online.

Anyone else interested in joining this initiative is very welcome.

Let’s use this forum to collaboratively improve the designs and identify business cases targeting a “Meetup-and-Build” session on 17th September.

As discussed, funding for the meetup-and-build session will come from community members and Gearbox will only facilitate the space, tools, materials sourcing and some expertise.

The advantage of participating in the online collaboration and the upcoming meetup-and-build session will be the very practical skills transfer gained to participants, who may later on want to build their own machines for sale or use.

We encourage your active participation to keep the innovation going.


Hey, I’m Clement from Taka Smart, we’re a startup that offers redeemable reward points to people in exchange for recyclable waste. We’re very much interesting in getting these machines for use in recycling plastics. We have a bunch of plastic bottles we’ve collected from our users so far.


Hey Clement, that’s great to hear! I just met another person today who is keen to help. He’s been extruding 3D printer filament for use making prosthetic limbs.

Are you able to join the next meetup on the 17th? It’d be great to get a bunch of us around to make a plan.


Yeah sure, I’d really love to attend the meetup, really excited to hear that there’s a movement around this.


Hey Habbes,

The objective of the 17th meetup is to actually build one of the machines if we can get the logistics and procurement funding organized beforehand, considering proposed improvements.

Hopefully we can do that work via this online forum.

Are you able to share any info on your stockpile;

  • how do you sort your collected plastics,
  • how do you clean them
  • approximately what quantity do you have
  • what was your idea about recycling

Kind regards,

A.Y. Sande.


Right now we have upwards of 4000 bottles, I’ll confirm the actual figures and update you.
The stockpile mostly consists of 500ML PET bottles, but we also have HDPE and other types and sizes. We have not yet weighed so we are sure of the exact weight. But we still have people bringing in bottles regularly.

We are still to sort and clean them.

Our initial idea was to sell these plastics to local companies which recycle them to manufacture other products like plastic lumber. However the demand seems lower than we had anticipated, especially for PET. And that’s the reason we’re looking in also doing part of the recycling ourselves to make other products. However we don’t have access to the equipment yet.




Get an Onshape account and review the Shredder CAD model linked below

Build Video:

CAD Model:


Awesome. Thanks for the info!

During the meetup, we discussed how the collection-cleaning-shredding-shipping process can be a sufficiently value adding to make a sustainable business.

Given your experience, however, it seems integrating vertically into use is vital.

Among ideas brainstormed include interlocking bricks and other construction materials

Would be great to brainstorm more uses for consideration even as plan to build the first machine.


Okay, I’ve checked out the model and the videos on Precious Plastic. But I must admit that we don’t have much experience in building and 3D-printing on our team. But we’re looking forward to learning from you, working together and making use of your expertise.


No worries, Clement, we’re getting excited to build this one, too. Expertise is less necessary than enthusiasm. We’ll try and get a few more people engaged in this discussion to figure out the next steps regarding:

  1. Funding
  2. Design (do we want to make any changes to the default?)
  3. Materials sourcing

If we can work those out, we should be able to actually build something on the 17th.


An immediate improvement I propose when fabricating a small number of the shredders is to replace the cast
bearing housing with a CNC milled part. Gearbox had good milling capabilities.

What other improvements would you propose to the design?


OK, so I finally managed to dive into the files provided by the Precious Plastic team and wrap my head around the bill of materials a bit.

It basically boils down to four components:

  1. The frame and hopper – mostly just steel tubing, with a bit of sheet metal. Details not crucial.

  2. The motor and driveshaft – an electric motor running at ~2kw at ~70rpm, and a specific size/shape driveshaft and set of bearings to fit the shredding knives.

  3. The shredding knives – a very specific set of laser cut sheet metal components.

  4. The electronics – pretty simple, just a power switch rated for a 2-3 hp motor, wired to run both forwards and backwards.

You can download the details, including their rather vague BOM here. They estimate it should cost ~180 euros all told. We’ve always had trouble finding scrap parts (especially things like functioning motors) very cheaply, so I’m expecting the entire project to cost somewhere between $200-$400 USD (20,000 - 40,000 KSh).

I’m willing to put in up to about $100 myself, but I’m hoping others are willing to join me in funding the project. We can track everyone’s individual contributions, so that if someone wants to buy the finished product, no one feels shortchanged. Otherwise, it can live at Gearbox where anyone can access it and it can serve as inspiration for folks to build more!

Here are some of my thoughts on sourcing:

  1. The frame – this is a bit too big to be made at Gearbox currently, so I’d outsource it to a job shop (I know a few who could knock something up). We shouldn’t build it until after we’ve sourced the other parts, however, as the shape of our motor might dictate some changes to the design.

  2. The motor and driveshaft – these depend a lot on what’s available. I’ll ask around, but will definitely need some help finding these.

  3. The shredding knives – Pipeman’s can do laser cut steel. I’ll try and get a quote this week.

  4. The electronics – shouldn’t be too hard to find down River Road or Nerokas if need be. What switches and cables we need will depend on the motor we get.

So the next steps as I see them are:

  1. Make sure we’ve got enough funding to actually build the thing.
  2. Find a motor. Most everything else depends on this.
  3. Get quotes for the items that need to be outsourced (the knives and frame).
  4. Gather the motor, knives, and electronics to assemble and test on the 17th!
  5. Once all that’s put together, we can design a frame to fit our components, have it made, and start shredding.

Looking forward to it!


Thanks for the great input @cpbirkelo, we look forward to the quotations.

Anyone else willing to help source some parts or improve design?

I will source quotations for the following components by mid this week:

  • 2kW single or 3 phase motor geared to output ~70 RPM, preferably used. This will drive specifications for the frame and hopper. Anyone know where to source one?
  • replace switch with contactor for 2 kW motor either single phase (15 amp contactor) or three phase (5 amp contactor)
  • two on/off buttons (red and green)
  • thermal overload protector - 5 amps for 3 phase motor
  • Off the shelf hexagonal shafts to be turned at the ends on a lathe
  • Off the shelf threaded rods
  • Off the shelf bearing housing


Update: I’ll source a Direct on Line (DOL) forward reverse motor starter which contains contactors, on/off buttons, thermal overload protector and enclosure. Similar to below;


Going to Pipe Manufacturers on North Airport Road tomorrow morning to get quotations for laser cutting steel parts and perhaps the frame.

Will also visit someone who sells motors in Mlolongo. He has a 3kW for 17,000/= but not geared - we may have to modify the design. Any ideas anyone?


Found a used 2kW motor with 10:1 reduction gearing at KES 35,000/-.

  • Need to test it for reliability under load
  • Need to raise the money for this or other motor

We also found gearboxes to use with any other motor


Early morning hunting for motors, this one is 1.5 kW with 20 rpm gearing - mainly used for hoists. Costs 35,000/- brand new from China.

We need to establish whether the low speed is acceptable for this project, assuming that grinding is not an on-demand process.

@cpbirkelo would you inquire at the PP forums


So, following the notes provided here:

and here:

It looks like the 20 RPM speed shouldn’t be a problem. Simply put, speed is important because too fast means it will throw plastic out of the hopper, but too slow means grinding takes forever. The slower it is, the more torque you get, however, meaning you can shred thicker plastics.

Following the formula provided on the pages above, Torque (Nm) = Power (Watts) / (RPM * 0.105), a 1500 W motor running at 20 RPM will provide 714.3 Nm of torque.

The only estimates I’ve found say that 20 Nm should be enough to shred bottle tops, while 60 Nm should be enough to shred “the front panel of a domestic appliance”. That sounds low to me, but regardless, ~700 Nm is undoubtedly enough to shred pretty much anything we want.

Of course, at 35,000 KSh, we’re blowing almost the entire budget on just the motor. We could look at smaller motors. Again, following the notes and formulas above, anything around 500 - 750 Watts (+/- 1 HP) running at any speed between 20 - 80 RPM, should provide enough torque, especially if the main use case we’re looking at is shredding PLA filament out of a 3D printer (it’s very soft).

The other important question is whether it’s single or three phase. A single phase motor is much more versatile, since you can plug it in anywhere. A three phase motor requires an industrial socket. It can potentially be adapted, but that requires some non-trivial rewiring.


HI. I am also willing to add some additional funding. I have up to 20,000 kes I can add. This might help with the motor.


If we pick a good motor, we could update the design so it interchangeably
works with both the filament extruder as well as a motor+ hydraulics
powered injection molder.

We could do this redesign at the next meetup with a motor on hand.

What does everyone else think?