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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All you’ve done here is create more walls using a single piece. If you want durability, your design will win as it allows for flex. If you want rigidity, it will be less rigid and take longer to make due to its complexity.
The loss in rigidity is due to creating weak points as the line turns. The gain in flexibility is exactly the same weakness but now a positive. It will take greater force from weight, butt less impact force.
If you’re after rigidity, either cram the space with as few complexities as possible, or fill space with triangles.
It’s not really clear what you’re saying, because they’re both “my design”. Could you specify 1 wall vs. 2 wall?
I think what that person is saying is that in your example the left part would probably be more durable because it is flexible and that the part on the right is less durable but more rigid, basically saying your result is expected and makes sense if you are wanting durability over rigidity.
I think that the part that is unclear is that OP is using durability, rigidity, and strength as they are defined by material science not in common English and they way they differ in definition makes that comment make sense. I’m not a material scientist though so I could be wrong.
I hope that is correct and makes sense hah!
The 1 walled hook has the infill resisting and pulling back as you try to straighten the hook. When it fails, some of the connections between infill and walls break, causing the hook to lose it’s form or original rigidity permanently. In the case of 2 walled hook, this damage should be less severe, making it more durable.
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.
It’s like making a truss vs just straight pipes.
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.
Shouldn’t that be obvious? The same way a bundle of hair is softer than a rod of the same thickness. The extreme of this are sandwiches like carbon - lightweight core - carbon. There, the parts that experience the biggest forces (the outermost layer in tension) is extremely stiff, while the core only needs to withstand compression to keep both apart.
