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If a part is wanted to be made the strongest possible, what slicer settings should be used?

  • 3-5 shells vs all shells, no infill?

  • 100% infill vs some other % infill?

  • Thin layer height vs thick layer height?

  • Any other relevant settings?

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If your real question is what would be the strongest then I say - the solid would be the strongest - no doubt.

But if the question is:

  • what be the strongest in comparison to weight or
  • what is the strongest in comparison to the cost (amount of material)

then these are good questions!

You can of course find many tutorials and comparisons on the net and there will be many answers - which all of them could be good/bad ;)

If these are your questions then instead of simple answer you can ask more questions like:

  • in which orientation or
  • for what purpose or
  • for continues stress or maybe for variable stress or
  • for bending forces / shearing forces or maybe tearing forces

all these forces and circumstances could require other answer... which could also lead to other questions :)

But according to my experience, the strongest settings (for general purpose) is 3 outlines (and the same number of first/last layers) and triangle infill 20-25 %

Why I think this is the strongest, 3 layers gives good chance to have well stickiness even if there are geometric/design issues and triangle infill gives good (and common) way to carry and spread forces.

But as I said it depends on many input data.

Let's look at these figures:

enter image description here

in figure A we have the strongest composition for compression; this is because all working forces try to damage material particles which is of course hard to do (depending on material density and length of polymers and the way they are tangled and so on - in general - material strength only).

If we consider figure B where forces try to tear apart layers then we know that we base on stickiness between layers which can vary on printing parameters (as is temperature and speed).

Finally, figure C shows shearing forces - in terms of layered structure it doesn't really differ from tearing apart but the results (the resistance of and object) is even weaker - it's because we base on stickiness and we additionally have less effective field of working stickiness) which reduces endurance of an object.

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  • $\begingroup$ I had seen some information (can't link from login required chat groups) that stated something like 95% infill would actually be stronger than 100%. This was the source of the question. $\endgroup$ – Eric Johnson Jan 17 '17 at 15:35
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    $\begingroup$ @EricJohnson this could be very interesting. I can imagine such situation but it would be really precise issue I suppose. 95% is so close to 100%. I can suspect this 5% (of empty space) gives some extra room to compensate bending so fibers can bend without tearing connections among them... it's possible for sure. $\endgroup$ – darth pixel Jan 17 '17 at 15:41
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This question is practically unanswerable without the load case or the part being known.

Input for the "strongest" part is depending on:

  • Load case (compression, tension, shear)
  • Part design
  • # of perimeters
  • Filament type
  • Infill percentage (incl. local increased infill for e.g. fasteners; see e.g. "Different infill in the same part")
  • Part orientation when slicing
  • etc.

Do note that 100 % infill does not guarantee the strongest solution, from ahoeben:

Final note: 100% infill is not always the strongest or best quality. If you overextrude by just a little bit, that will quickly add up with 100% infill. With a lower % of infill, the overextruded material has somewhere to go.

There can also be issues with cooling with high amounts of infill; you are not only putting more material on the print, but also more heat. On the other hand printing a layer is going to take a long time, so there should be time to cool. But shrinking/warping while cooling is also something that is affected by the amount of material.

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