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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.
Okay, but if my 2-wall hook bends into a straight line, then I don't really care about the durability of that no-longer-hook-shaped object.
Edit: I agree that 2-wall could make sense, if your goal is to reuse the hook (with a more appropriate load) after the heavy load falls off. That's analogous to protecting a wire with a circuit breaker.