"Rules??? We don't need no stinkin' rules!!!" - Various (but may have started in "Treasure of the Sierra Madre")
"They're not actually rules as such. More like guidelines" - Capt. Barbossa - "Pirates of the Caribbean"
Pretty much every model has it's own needs. Saying "this is always how you do it" isn't going to work very often because there will always be an "Except when _____ _____ ______."
Ok, let's settle on guidelines.
I was hoping there would be some recommendations. Let's say you go up to 5 layers top/bottom and 6 walls and line multiplier of 2 with 10% infill. So if you want to get it stiffer, is more walls or a bigger multiplier better. I was hoping somebody did such tests.
Edited by shoe
What material were you thinking of using? PLA is very rigid but when it warms up it will deform. PETG is more compliant but has better heat deformation resistance.
I have managed to run over a print with my car. It had single line infill at around 10% and it was fine. If it would have been larger so that there was more distance between the walls then the upper layers may have crushed.
There have been a couple of posters here who were involved in some FEA analysis of FDM prints. They asked a couple of questions and were gone. I've never seen any results from an analysis of that type.
Overall strength in compression is actually pretty good. It depends on the shape of the model and the force loading to know how it will hold up.
A compression load on a screw connection is another story. Cold flow deformation at the screw head and at the face of the nut will cause the connection to loosen. That will happen every time with either PLA or PETG. The warmer the environment the worse the condition and the quicker the failure.
Overall strength in tension is not good. The layer adhesion is the main weak point and so in that case more walls can't hurt.
If there is a twisting moment in the loading so that one side of a model is in tension and the other side in compression then the layers will fail do to the tension before the compressed side fails.
If you do a search for FEA (Finite Element Analysis) of FDM models maybe something will come up that you can use.
Edited by GregValiant
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GregValiant 1,251
I think "Grid" is the best all purpose infill. With the "Infill Line Multiplier" at 3 you will get a noticeable increase in stiffness. I would think an Infill Density of 10% at 3 lines thick would be sufficient. Changing the Infill Line Directions to [0,90] might help as well. The "best" line directions would depend on the directions of the load that you expect the part to see.
If you require the stiffness because the part will see some sort of twisting load then Wall Thickness and Layer Height will become more important.
"Is there a rule of thumb as to best determine all the parameters for a given amount of filament I want to use for printing the plate?"
"The amount of filament I want to use" is something I've never considered. The volume of filament is-what-it-is depending on the geometry of the part and the infill structure it requires to perform the function it was designed to.
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shoe 1
Well. Amount of filament. Print time. Whatever metric you want to use. I don't want to waste time and money (PLA, electricity). Common wisdom is to increase the outer shell (top, bottom, walls). It seems infill plays almost no role in "strength" and "stiffness". Maybe I am mistaken.
But maybe beyond a certain wall count (e.g. 6), this rule doesn't hold true and it makes more sense then to increase infill to get better strength/stiffness.
Those kind of rules I was hoping for. For example, for every two walls increase infill by 10%. Rules like that.
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