Bloft Mk2 - 3D printer for plastic waste

An open source large format 3D-printer for plastic re-/upcycling

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The project has set the goal of developing a micro factory with built-in capabilities for plastic recycling. In the sense of throwing in plastic waste at one end and getting out a new product at the other end. The core of this micro factory is the Bloft Mk2 large format 3D-printer which accepts plastic flakes (but also plastic pellets) as printing material. The printer is equipped with small pellet extruder with an average throughput of 2 kg per hour. Under optimal conditions and ongoing operations the printer should be able to recycle up to 20 tonnes of plastic per year.

The printer is a cable-driven delta setup with a footprint of ca. 4.5 meter in dia and +4.5 meter height. The effective print volume is a cylinder of around 1000 x 2500-2700 mm.

The system is based on a modular truss system for easy extension and transport to enable customization and print-on-site operations. Bloft Mk2 has its origins in the Hangprinter project by Torbjorn Ludvigsen.

What's it all about?


This project started initially as a sidekick during my industrial design studies. In 2018 I stumbled upon the Hangprinter project which had an unique cable-driven motion system. Instantly I understood the potential of this concept over anything else what comes to expendability.

I built a Hangprinter v3.2 during the summer break during which I had access to the university's labs and workshops. The Hangprinter is meant to be attached to the ceiling of a room and having anchor points at floor level for pivoting the lines responsible for XY-movement. Ceiling attachment was right away out of question because of the high ceiling. So, I needed to start working on a frame design first.

The outcome was a lightweight frame made of square aluminum profile. There was a smaller beam inside a larger one and a clamping mechanism locking them together in place. That way I could adjust the size of the frame. The print surface was a 8 mm thick tempered glass table top laying on top of height adjustable standoffs. These were meant for leveling the bed.

Calibration of the Hangprinter proved to be extremely difficult due to the non-linear kinematics which required exact measurements of the anchor points and line lengths. I don't want to imagine what it would have been without a frame. Luckily nowadays Torbjorn has developed an auto-calibration system based on visual position feedback of the end effector and some nice scripts.

After first prints the frame was enhanced with a couple of tweaks here and there. Then in 2019 we got the change to use the printer first time for a commercial print project for the Finnish shoe designer Minna Parikka. She wanted to have a huge 1 meter tall replica of her iconic Joan high heel to be placed in front of her flagship store in Helsinki. We accepted the challenge and it took the printer (and us) to the limits of what was possible. But at the end of the day we were very proud of the outcome.

From FDM extrusion to FGF extrusion

At this point we still used a FDM extruder for printing. Which in hindsight was a mind-blowing lesson for us. Once we started calculating how much money and resources were wasted by not being able to reuse print supports and failed prints, we pretty fast concluded there is no future for FDM in this class of 3D printers.

In 2018/19 first pellet extruders for 3D printers popped on the surface, like the Mahor Pellet Extruder. After going through some reviews and having had a look on the CAD models we considered it too small for our intensions. Commercial pellet extruders like the Pulsar extruder were closer to our specs, but unfortunately they were completely out of our budget. Instead we decided to develop our own based on the 16 mm compression screw from RobotDigg. Out came our Badass Pellet Extruder.

You can check early steps of the development on the RepRap Forum

After the initial design & development stage we were pretty quick to get first extrusions with plastic flakes. But now we lacked a printer sturdy and strong enough for the pellet extruder :) Together with a new end effector made of steel we were looking at around 10 kg of mass. It was way too much for the Hangprinter to bear. This is when development of the Bloft Mk2 started. It had to be designed from scratch, with semi-industrial application in mind from the beginning.

The Bloft Mk2

We founded Bloft Design Lab in 2019 to start commercial development of the printer. In early 2020 we were chosen to participate in the Baltic Sea Challenge agile experiment by the City of Helsinki to test the 3D printability of marine/beach plastic waste for which the experiment was setup to find new recycling methods. The plastic that was collected by volunteers at the Helsinki shoreline was injection molded into standard tensile strength test specimens. These were tested at our university's material test lab. The results revealed only marginally...

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  • How does the plastic recycling process look like?

    Atte Linna09/12/2022 at 13:02 0 comments

    As lovely as it would be, plastic recycling by 3D-printing does not work by just pushing the print button. Actually, 3D-printing is the last step in the process. Let's have a closer look on the whole process.

    First of all, you need plastic. It can be collected from your local beach, your local businesses can deliver it to you for recycling or you can use your own plastic waste streams. The origin of the plastic, its age and its previous use determine the state of degradation of the material and hence its potential use cases. 

    Plastic degradation

    Plastic degradation means the degree of broken polymer chains of the plastic. The more breakage has occurred and the shorter the polymer chains have become, the more degraded the source material is. In plastic recycling it is common to mix a small percentage of virgin plastic with the recycled one to enhance the material properties. As a rule of thumb though, you can recycle plastic up to ten times without remarkable degradation. 

    Degradation occurs because of different reasons:

    • UV-exposure (usually Sun light)
    • Oxidation
    • Exposure to chemicals (incl. saline water)
    • Thermal cycling (aka recycling)

    Even though the ten recycles are considered the safe limit for recycling a certain plastic, there has been an interesting research on Processability and mechanical properties of extensively recycled high density polyethylene by Pavel Oblak & co. in 2015. In a nutshell the research group recycled HDPE 100 times and observed the materials behavior during this test. As a conclusion, it is possible to recycle HDPE more than ten times, but you have to put in more energy into processing due to cross-linking of the material.

    Identification of the plastic type

    Sorting the source material is key for quality outcome of the recycling process. There are 6 main plastic types which you can identify at best by their resin identification codes.

    And then there are the others, which make the whole thing a bit harder. Thermoplastics in the category 7 can include technical plastic types like ABS, PC, POM, etc. But they can include also plastic blends or inseparable multi material foils (used often in the food packaging industry).

    Currently we do identification and sorting still manually, but as we get further with the development, we will switch over to automated identification by NIR spectroscopy. This process illuminates the sample with near infrared light and detects the reflection throughout the IR bandwidth. Based on the histogram fingerprint of the plastic you can identify its resin and sort it accordingly.

    Shredding the plastic objects

    As Bloft Mk2 makes use of plastic flakes or pellets, we need to first shred the objects into small pieces. There are already plenty of industrial shredders and open-source alternatives like the Precious Plastic shredders. These machines typically produce a flake size of ca. 3-5 mm which is close to the size of commercial virgin plastic pellets. Prior to shredding it might be necessary to pre-clean the plastic for instance to get rid of sand and other debris that could damage the shredder blades.

    Washing the plastic flakes

    The cleaner the plastic, the better the outcome. Most of the packaging comes with some sort of label added. Ideally this label is made from the same material as the packaging, but unfortunately there's no guarantee for that. Peeling off the label might work, but it is a tedious task, which can and should be automated. Precious Plastic has already developed a basic washing machine which uses pressurized water to blow off dirt. This might work well for dirt, but it might not work for labels. One option could be a combination of a water jet and some abrasive additives like sand as in sand blasting. But then again we would have a soup of mixed plastic which would need to be sorted again. As you see, the washing/sorting part is important and at the same time complicated to manage. This part of the process needs more research and time.


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  • Bad Ass Pellet Extruder v1.0

    Atte Linna08/31/2022 at 14:31 0 comments

    The Hangprinter project by Torbjørn Ludvigsen has developed a promising and affordable concept for a large scale cable-driven 3D-printer, that has the potential to serve as the framework for an entirely new class of 3D-printers, enabling distributed local manufacturing of large end use products like furniture, vehicles, buildings etc. Up until now the Hangprinter has relied on regular FDM-extruders leaving the project far behind its true potential. Being great for desktop printers, those extruders are not suitable for printers beyond the 1 cubic meter class. Filament extrusion hits the wall in terms of speed, cost and sustainability.

    We decided to circumvent this obstacle by developing an affordable pellet extruder, that enables you to print not only with industry standard plastic pellets, but also and mainly with re-granulate plastic made from your plastic waste.

    Design Drivers

    • Throughput 1-2 kg/hr depending on polymer
    • As light as possible
    • Nozzle sizes up to 10 mm, easy to swap
    • Sturdy base for attachment
    • Enough heating power to cover as many polymers as possible
    • Tolerance for potential foreign objects (dirt, sand, etc.) within the granulate
    • Automatic material transport and dispensing
    • High flow cooling for the print area

    The compression screw

    The compression screw is the key element of a pellet extruder. It differs from a regular auger bit by having a flute depth that decreases towards the tip. The compression screw is disected into three different zones: the feed zone, the compression zone and the metering zone. The screw adds shear to the plastic granulate and accelerates the melting process. These compression screws are difficult to manufacture, so we are going to cut corners and we will use the RobotDigg 16 mm extruder screw, barrel and nozzle for now.

    The RobotDigg barrel has already a flange with standard Nema 23 attachment holes and it comes with an exchangeable nozzle.

    • Compression ratio 2.5


    Certain set of tools is needed to start your own project. Both software and hardware tools. We are designing the pellet extruder in Autodesk Fusion 360. Although not open source, you can obtain a personal, non-commercial, license for free from Autodesk. We will provide also exchange file formats if you prefer to use other CAD software.

    Among other things you should be prepared to have access to following tools:

    • Drill bench
    • Soldering iron
    • 3D-printer
    • CNC-machine
    • Handtools like allen keys, wrenches, screw drivers, metal saw etc.

    A word of warning

    The barrel is heated by powerful mica band heaters. This leads to two serious hazards.

    1. The heaters are powered by grid voltage which poses a danger of a lethal electric shock! If you are not trained in connecting electric circuitry, please ask someone with experience.
    2. The heater bands can generate heat up to 450 degree Celcius, which can lead to serious burn injuries or a fire hazard.

    Please keep this always in mind. Ask always, if in doubt.


    • 09/2019 - 11/2019 Design, component selection
    • 11/2019 - 12/2019 Manufacturing, assembly
    • 01/2020 - 06/2020 Extrusion testing, iteration
    • 01/2021 - 02/2021 Print testing

    Project on Github

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  • 1
    Component sourcing
    This is the Badass Pellet Extruder v1.0 which we are going to assemble here.

    First of all, you will need to source all the components.

    The BOM can be found here:

    The most recent design files are kept on AutoDesk Cloud which you can access here:

    The extruder uses the 16 mm compression screw and barrel from RobotDigg which 57 mm flange is compatible with Nema 23/24 size steppers. You will need to choose a stepper with adequate down gearing for enough torque. The needed torque depends on the flow properties of the polymer you would like to extrude and of course on the targeted speed. A 25:1 reduction is a good spot to start with.

    You can buy different sized nozzles from RobotDigg. 

  • 2
    Safety Warnings

    The Badass Pellet Extruder is powered by mains voltage which can cause a lethal electric shock if connections short circuit for any reasons! Therefore it is mandatory to have experience in building safe electrical circuits. Do not ignore this warning!

    All metal parts of the extruder need to be grounded to Protective Earth and the electricity powering the heaters should go through a residual-current relay which might be your lifesaver if things go south. 

    The maximum temperature of the heater bands is around 300 deg C which can lead to serious burn injuries and/or a fire. Those heaters will need an insulation blanket. Do not operate the extruder without them and remember that due to the large thermal mass of the extruder it will stay hot for a long time after power is shut off.

    Ideally only the nozzle is exposed and hot.

    This extruder is a prototype design. We do not bear any responsibility for loss/damage of life, health or property that results of using this extruder. Please be responsible and careful!

    We expect you to have the expertise to connect the extruder to the mains grid, therefore we won't give any advice on how to do that.

  • 3

    You will need basic tools like metric Allen keys, some pliers, screwdrivers, hacksaw etc. A Dremel is also very handy to have. You'll need to cut the mixer screw to an appropriate length and also to remodel the tip of the screw. Have some cutting discs and grinding tips available.

    Some power tools like an electric drill come handy as well. Depending on how you will want to terminate the wiring you will need a soldering iron too. The soldering iron is also needed to insert some heat inserts.

    Beyond the things mentioned above you should have access to a 3D-printer.

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