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Comment by traverseda | Hacker News Reader

I think they need to release a 3D printable version. 3D printing is going to be more expensive and more fragile than injection molding, but being able to print a replacement ball connector or the like is one way this can become a lot more resilient, other than having multiple manufacturers. If they want to become something like a standard then having a work around for that kind of supply chain issue is important, I think.

EDIT: They do appear to make "simplified" 3D models available for download from their hub-part-specs pdf. I suspect with a high layer height like 0.3mm you could print replacements. I understand why they don't advertise this though.

https://buildwithhubs.co.uk/downloads/hubs-part-specs.pdf

https://buildwithhubs.co.uk/downloads/hubs-cad-models.zip

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Rather I think they should release a metal only version. I don't trust plastic to live a long and prosperous life in outside conditions, those are not where plastic shines.

As for 3D printing, I guess ABS could work (PLA can melt or become soft in the sun), but I can't imagine a hobbist grade printer producing a part that is comparably strong. The option would still be nice, though. Maybe you just need a prop for the theater, where weather is a non-issue, and being able to replace parts quickly is more important than longevity.

You can definitely print strong enough parts, most 3D printer slicing software is optimized to reduce material cost not to create strong parts. Increasing the number of walls is a good place to start.

PETG is a better choice for outdoor use than PLA or ABS.

You want thermoplastics sitting out in the sun being part of the structural system of a building? That seems like a recipe for a building collapse.

I think the term "building" is a bit of a stretch. Mostly the geodesic domes seem to be used as small greenhouses, and don't have enough weight that even a sudden collapse would really damage the occupants. The manual suggest that the maximum weight for the whole structure should be about 60kg. I'm not really concerned that these things aren't meeting fire code either, you know? You can just pick a wall and tear through it in almost all the examples I've seen in the gallery.

That being said the glass transition point of ABS plastic is 105'c, a little over boiling. I'm not worried about ABS from a thermoplastic perspective, although I am worried about long-term UV performance. I'd also be worried about thermal cycles and plants/mold as most 3D printed ABS will take on water.

I think you'd get a few years out of an ABS plastic component in these circumstances, more if you resin coat it or use acetone vapor smoothing, and start with a filament that has good UV resistance.

Either way I expect 3D printed components to be more expensive and otherwise worse than one manufactured by this company, but being able to repair stuff like this if you need to is important and it's not like you can just go to the hardware store and get a replacement one of these hubs.

Everyone always seems to overlook you can just paint the parts for UV protection

I'm not sure how that would interact with the mating surfaces in this particular design, I suppose you could paint it after it's already in place though.

There are entry-level consumer filaments that would withstand the UV and heat requirements for outdoor use, such as PETG which is UV stable and as strong as ABS.

By entry-level I mean able to be printed on the everymans Ender 3, <$300 printer with little expertise. There are of course dozens of exotic filaments you can print on a slightly more advanced machine and even that can be done for pretty cheap, <$500 perhaps if you have the expertise to upgrade an Ender and tune it properly.

The benefit injection molding has over printing in this case, is these parts might want to be redesigned to reduce sheering at the layer lines on the peg things.

UV stability is only one aspect. What happens when you build a greenhouse out of these and the temps reach high enough to deform these? How long do you think the structure will stay stable with or without UV paint?

I've had a greenhouse melt nursery pots left in it and they're made out of polypropylene, which has a glass temp 50C higher than ABS.

The inside of your greenhouse is reaching ~150 degrees celsius? Why aren't your plants boiling? Is it just a color thing?

EDIT: the glass transition point of PP is -25C, vs ABS's 105c. I think you confused glass transition point with melting point, they're very different things. I think polypropylene will always be a bit soft, and will hold a shape that it's deformed into, it it hold that shape long enough.

Sorry I think you might just be mistaken. If your greenhouse is reaching 150c then there's actually not that many common plastics that wouldn't hit the glass transition temp. There are some exotic "plastic blends" like glass or carbon fibre/mineral blends that can do it, but even most of those are less than 140c. In this table even the modified versions of polypropylene have glass transition temperatures below negative: https://omnexus.specialchem.com/polymer-properties/propertie...

I don't think it should be too surprising that 3D printing filaments can withstand similar characteristics to other outdoor plastics. One commonly used outdoor plastic is PVC which has a glass transition temp between PETG and ABS: PETG: 80c, PVC: 85c, ABS: 103c. If you left a PVC pipe in your greenhouse you wouldn't expect it to deform.

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