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Comment by hengheng | Hacker News Reader

Really depends on what material you're pushing.

PLA is not strong and doesn't like to warm up in the sun, Silk PLA (made to just look nice on the shelf) can even be brittle. But there are better materials.

PETG is entirely reasonable, I store my pots and pans on PETG hooks and they're not oversized. The superior 3d printers can print ABS which is above any and all doubt.

There are also specialized materials, such as carbon infused PETG, and there are engineering materials at 500€/kg with some interesting properties. But the gist is that PLA makes you go "this sucks, must be printed", and PETG makes you go "oh this is fine".

Then there are resin printers that selectively UV cure a liquid to polymerize it. Last I tried that sticky goo it was awfully brittle and borderline unusuable. I heard it improved, but that's why resin printing is not everyday parts but figurines.

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Regular PLA is actually stiffer than PETG/ABS, but it's more brittle (so has less impact strength) and a pure formulation has a lower softening temperature. It's generally not suitable for parts that go under the sun, unless it's some other formulation such as some HT-PLA variant, in which case it's actually a good choice for parts that need to be thin and stiff.

Under most cases, you won't get the same inter-layer adhesion with ABS, so while you get better impact resistance, under most circumstances PETG will yield more durable parts that won't delaminate under the same stress conditions. For outside use under the sun, you should use it's cousin ASA.

To respond to the OP.. 3D printed parts can be incredibly durable when printed correctly. The parts need to be designed for 3d-printing in mind, like most other manufacturing methods. A 1cm-thick 15% filled PLA slab that has been printed vertically might be easy to snap in half with two hands, but it becomes almost impossible to break with bare hands when printed horizontal, and requires a saw to be cut when filled to 50%+. And this using consumer-grade printers.

I'm using 3d-printed parts for work and at home, some in use for almost 7 years at this point, and the only telltale sign is the layered look.

The rods in the design are not 3d-printed, which makes sense (most plastics would be too flexible, and 3d-printing a rod is always more expensive).

You can get excellent inter-layer adhesion with ABS, if you crank temperature up and disable cooling.

I print on a Mk3s in a photo tent and have had no trouble eliminating layer failures as an issue.

> that's why resin printing is not everyday parts but figurines.

It's probably more to do with it being messy, smelly, and overly finicky business[0] compared with FDM (but there's zero chance of burning your house down, I suppose.)

[0] levelling the build plate, cleaning the FEP on failures, replacing the FEP, washing the results with IPA (mostly), having to keep the resin warm to get good results, draining the resin when not used for a while, faffing about with orientation and supports is a black art, etc.

> PLA is not strong and doesn't like to warm up in the sun

"Strong" is ambiguous. PLA is stiffer than many other thermoplastics (resists bending loads well), but it's not as tough (impact strength is poor/it's brittle).

PLA becomes even stiffer and resists higher temperatures than many other thermoplastics if you anneal it.

You want stiffness in a telescope because deflecting under load moves your optics out of alignment. A telescope has moving masses as well, so stiffness along all axes under load is important.

I've often found PLA to be fine. But small features on a large part can break if dropped.

Of course it all depends on you application.

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