See also : Haiti: Ruminations
I started this project with a simple goal in mind. Build the 4 machines outlined on Dave Hakken’s Precious Plastic website, then build them again in Haiti. It is said that no plan survives first contact with the enemy, and this story is no different.
When I left Haiti last week, I walked away from one functional machine, one untested machine, and one that barely worked at all. The fourth machine, we didn’t even try. Here I plan on taking an unflinching look at my successes, my failures, and the path that got me to them. Please settle in, this could get long. And boring…
This particular story starts in May, 2016. My cousin Sarah, a midwife in Haiti, discovered the Precious Plastic website, and contacted me to ask if I thought the plans were reasonable, and could work for her. She works with a lot of people in Haiti, trying to find sustainable sources of income. This, she reasoned could be another. My initial response was “I dunno. Let me look into it”, followed a few days later by “I dunno, but let me try”. I presented the plan at a Diyode meeting shortly there-after, and managed to convince a few other people to help. Notably Eva, Brennan, and Liam, who were instrumental in getting the machines as far as we did.
Now, my first mistake was thinking that 8 months was enough time to get these built, using an evening or so a week, and maybe some time on Saturday mornings. I also should have put on my project managers hat at the start, figured out timelines and deadlines, set some milestones, and thrown the whole thing on Trello. But my tinkerer’s heart is weak, and I just wanted to get started. I also had a great deal to learn about the tools I would need to use. The metal lathe and plasma welder would play prominent roles in the project, and I wanted to get more proficient with both.
The Shredder Build
The first machine that I tackled was the shredder, since without the shredder, the other machines just take up space. I decided to work with Hakken’s basic design in metric, meaning that the laser cutting would have to be done outside of North America. No one in North America that I contacted had access to metric thicknesses of stainless steel. I found a company in China that would cut them out, and actually do it cheaper than anything I could get done locally. I adjusted the dxf files to work with stainless steel hex bar stock that was easily available on North America, and we were off to the races. In hindsight, I should have also added mounting holes for the shredder and hopper, as I had to drill these later.
One of my design criteria for the shredder was that I wanted it to be built out of commonly available parts, so that it could be repaired using commonly available parts. In the Precious Plastics build notes, it says “scavenge a motor that runs at 70rpm, and 100N*m of torque”. OF course, scavenging in North America is no longer possible for the most part, and Hakkens gives no indication of what sort of machine this type of motor comes from. I struggled for a while with the best way forward with this. 100Nm is a LOT of torque, but at 100rpm (what I had geared down to), it was achievable with a 1.5HP motor. The motor cost me CAN$300, but can be gotten in the US for US$150.
For gearing, we experimented with several options. In the end, I decided to go with dual v-belts from the motor to a pair of 10″ pulleys. That transfers through a bearing to a pair of 12 tooth bike chain sprockets. The other end of the bike chains are 56 tooth sprockets from a mountain bike, welded to a tube that mates with the shredder head axle. This all made for a fairly complex build, but quite forgiving, in the end. The motor put off enough torque, and the belts and pulleys transferred it well. In the end, the weak points where the generator running the motor (it would cough and sputter when the motor pulled too many amps) and the shear pin between sprocket and the shredder head. The axle broke through every shear pin we threw at it, until we got up to a 3/8″ hardened steel motorcycle bolt. At this point, I was worried that there wasn’t enough stock left on the axle to stand up to the torque, since we had drilled the shear pin hole so big (the axle is 20mm diameter at the point where the shear pin connects, leaving just 5mm of steel on either side of the shear pin). This arrangement seemed to stand up ok, but I did notice there was some deformation of the shaft around the pin after some use, so I am not fully confident it will last forever.
If I had to do the shredder again (and I probably do), I suspect I would bite the bullet and go with an appropriate worm gear. This means lubrication is much more important, and we are no longer dealing in generic parts at all (The worm gear parts would probably cost $100 from somewhere like McMaster Carr), but the build would have been so much easier. I’m still mulling this over, though, and am open to suggestions.
So, now we have a fully functional shredder, except, it still ain’t perfect. You see, bottles have a tendency to just bounce around on top of the shredder teeth. This means pushing on them with something, or stopping the machine and reaching in to re-orient the bottle. Ideally, the shredder should be able to operate with no intervention. Just chew through whatever you put in until it’s done. This, however, was not the case. Also, even at 108 Nm of torque, it still struggled sometime with the hard plastic at the top of the bottles. It’s close to strong enough, and gearing down to 60 or 70 rpm would probably give it enough punch. I tried arranging the teeth in a spiral, a point (a spiral that reverses at the middle point) and randomly. A spiral seems to be optimum for minimizing the bouncing of the bottles. In some cases, a bottle would line up under the teeth, and cause a momentary spike in the required torque, but I am hoping by increasing the torque that little bit, that will address that as well. I am also playing with the idea of putting a heavy flywheel on the motor side of the gearing, but I need a better shear pin set up for that, I think.
The Extruder Build
Oh man, this one gave us some trouble. And by us, I mean mostly Brennan and Eva, who absorbed much of the stress here.
Our biggest issue, the one that held us up for the longest, was with the extruder screw. We spent a lot of time looking for a screw solution that resembled the screws used in commercial extruder system. Our first option was to get a 24″ long, 1″ diameter fluted masonry bit. The cross sectional profile was good, but it was 2 fluted, and as such had a very aggressive pitch on the fluting. The other issue was that only the carbide on the point of the drill was 1″. The rest of the shaft was somewhere around 7/8″, but not even close to precise. Once we’d cut off the carbide, we were left with something that didn’t really fit into any commercially available pipe.
Our next option (and the one we shipped with) was a 1″ wood auger bit from McMaster Carr. This was precision ground along the whole shaft, fit well inside the stainless pipe, and looked to be quite reasonable. The profile was quite different from what is typically used, but I think it should work. Sarah will be testing it once she has the time and power at the same time. I’ll report back.
What I plan on doing, once I get some time, is create a custom jig for the milling machine that will allow us to machine custom screw profiles out of solid steel rod
For the body of the extruder, we started with stainless pipe, cut out the hopper hole, and welded on plates for the hopper to attach to, and two very hefty feet for it to mount to the frame. For the extrusion nozzle, we didn’t go with the end cap style interchangeable nozzles in Hakken’s designs. Instead we welded a solid plate to the front that we could bolt other plates to. If you go with this design, try to minimize the amount of metal you put on the front, as this will be a significant heat sink, if it is too big.
Another thing that tripped us up is that stainless steel warps very easily while being welded. Much more so than normal steel, it seems. Brennan, an experienced welder, took what he thought were small enough welds on the pipe, but once it cooled and we reinserted the auger bit, it was clearly significantly warped. Brennan was able to bend it back into shape with much effort, but it was not a fun job.
For the electronics on the extruder, we used a 100rpm 12VDC motor from MakerMotor.com, with a digital speed controller, and a 12v DC power supply design for high wattage LED installations. The band heaters were controlled by simple PID controllers bought off of Amazon, that came a solid state relay and K-type thermocouple.
My last lesson learned on this is tho avoid too much mass on the extruder tube. We felt, during the design stage, that the tube should be able to handle high pressures and high torques. We welded extra cladding onto the business end of the nozzle, extremely solid mounting feet, and a heavy front plate. In hindsight, we may have over-estimated these factors, as this meant that the band heaters really struggled to heat up the tube.
We completed the extruder build on the second last day of the trip, fired it up, and got the auger spinning, and the tube heating, but we didn’t have any plastic pellets ready to put into it. Then the power went out, and didn’t come back on until after we left for the airport.
The Compression Oven Build
The oven was the one item that I went down with a very ill-formed plan on how I was going to get done. Sarah had told me that she had an old autoclave that could be used for parts, but not knowing what it looked like on the inside, I decided to just wing it. Our preparations in the weeks before leaving had gotten a bit desperate, and I was happy to take the oven off my plate in favour of the other machines. Plus, I reasoned, it was the simplest build, and the one that most relied on what we would be able to scrounge once we arrived. I was pretty sure I could get it heating with a PID controller and a solid state relay, and that with enough time to throw at it, I could probably pull something off. So, flying by the seat of my pants, I decided to make most of my decisions down there. For the compression mechanism, I reasoned that there would be plenty of access to car jacks of one sort or another down there (wrong!). For the oven part, I assumed I would be able to scavenge parts from an electric oven (Oh so very very wrong), and insulation to put around it (holy hell, are we starting to see a pattern here?). I had no luck finding an old car jack. No-one has electric ovens in Haiti. They are all gas, as the electrical supply is so unreliable. And lastly, Haitians have very little need of insulation, since it doesn’t get cold, and almost no-one has air conditioning. Freezers are everywhere, but not clad in heat resistant insulation, more likely to be styrofoam. Given more time, I may have been able to find an old gas stove to take apart for some fibreglass batting, but alas, time was too short for that.
I was able to get my hands on the old autoclave. This provided a small heating element, and so we built as small an oven as we could. But without insulation, it was radiating heat as fast as I could pump it in, so getting up to temperature was damn near impossible. I’m pretty sure that with a good thickness of insulation, and an outer metal shell, it is much more likely to work well.
My other compromise, which I am also second guessing at this point, was with the compression mechanism. The precious plastics design calls for a car jack underneath the oven. All that I could find on the ground in Haiti was a trailer tongue jack. Since those are designed to be jacked from the top, the only good way to arrange it was with the jack on top of the oven. This means that there is less space between the heating element and the plastic being melted, and probably uneven heat. Jacking from the bottom really is the optimal arrangement.
My plan for compression forms was to make plates and bowls. Before leaving Canada, I bought a variety of stainless steel bowls and enamelled camping plates. These seem like a really good place to start, and Sarah has had some luck getting plastic in them to melt and form, just not with enough heat to get a nice solid shape yet. If I had time, I would also fabricate a custom fitted metal cylinder for each set of forms, to help guide the compression. Having not successfully made anything with the oven yet, take this with a grain of salt.