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Sometimes fewer walls are better
(media.kbin.run)
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.
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 ?
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.
Nice! Thanks for the work and reply 😊
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.