this post was submitted on 18 Feb 2024
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119
Sometimes fewer walls are better (media.kbin.run)
submitted 9 months ago by [email protected] to c/[email protected]
19 comments fedilink hide all child comments
 

I think I found a counterexample to the common wisdom that more walls always create a stronger part.

The pictured S shape is 1.5mm thick, so printing with 2 walls leaves no room for infill. My testing wasn't very rigorous, but it seems that the hybrid structure of walls + rectilinear infill is 10-20% more rigid than walls alone. The infill adds strength by cris-crossing between adjacent layers.

I think it's fine to include a concentric top/bottom layer, but multiple identical layers weaken the part. I also tried 0 walls (infill only) and that was garbage.

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[–] [email protected] 10 points 9 months ago (2 children)

What testing did you complete? Curious to find out how you found it stronger. As in if this is done as a hook, can it hold more load ?

[–] [email protected] 10 points 9 months ago* (last edited 9 months ago) (1 children)

I just tested this hook by hanging a 5 gallon bucket and gradually adding water. PLA 1 wall = 1710 g, 2 wall = 1178 g. The thing is, a 1.5 mm hook fails by straightening rather than snapping, so rigidity is more important than strength.

Edit: I also tried PETG: 1 wall = 1441 g, 2wall <998 g (failed to hold the empty bucket)

So the 1 wall hooks can support >40% more weight before straightening enough that the bucket slips off. That's more significant that I expected.

Edit2: Part of that 40% difference is due to friction; the 1-wall hook has a rough surface that makes the bucket less likely to slip off. But even with bluetack on the hooks, 1-wall has less deflection than 2-wall for the same weight.

Another confounding variable is the weight of the hook itself: 2-wall = (0.83g slicer, 0.78g actual); 1-wall = (0.95g slicer, 0.88g actual). I don't know if that extra weight is coming from density or volume, but either way the stronger hook is more expensive.

Sigh, reality is so complicated.

[–] [email protected] 3 points 9 months ago

Nice! Thanks for the work and reply 😊

[–] [email protected] 6 points 9 months ago

Lock some calipers (with a rod sticking out) to 1.5mm shorter than the part height, compress it down onto a kitchen scale until the rod is just touching the platform, and record the weight.

That's just the first procedure that came to mind. I will try to think of a way to do a hook strength test today.