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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.
Really interesting! I wonder what would happen if you combine these two properties. Suppose some length of the middle is all walls, and the hooks are infill, or vice versa. Is there an optimal mix that maximizes the weight it can support in your testing, or have you found the optimal configuration (with infill along the entire length) already?
I haven't done any tests where the tensile/breaking strength is relevant, just rigidity. Maybe it's possible to optimize the infill based on finite element analysis or something, but that's not a rabbit hole I'm looking to go down.
I have tested that an all-walls sandwich (PrusaSlicer "solid infill every 3 layers") does not improve rigidity. So far nothing beats 1-wall + rectilinear in that department.