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Looking in the Cura interface, I can set any whole number 0-100 for the infill percentage. Does Cura have an algorithm to calculate a pattern for any of those possible values, or does it have a few patterns where it selects the closest one?

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  • $\begingroup$ it has several algos, names like grid, triangles, etc. It then scales the amount of "wallage" to the infill percentage; shrinking or expanding the pattern as needed to achieve a specified infill ratio. $\endgroup$ – dandavis Aug 10 '18 at 22:38
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Infill serves two main purposes. These don't seem to map particularly well to the available controls.

Adding strength to the part The more plastic your part has inside, the stronger it will be. At least, that is the simplistic assumption. In fact, it seems that infill is not a particularly effective way of strengthening a part (compared for example with thicker walls and structural design features). What is apparent is that some infill patterns are stronger in certain directions, some are more isotropic, and some are just weak.

Supporting upper layers Without infill, any top faces on a model will involve bridging, so there is a trade-off between infill density, the number of top layers, and the quality of the top surface of your print. To reflect this function, slicers allow you to incrementally increase the infill density as you approach a top surface. This is particularly useful in a model that has a large inner void which does not otherwise need to be filled.

In addition to affecting the infill strength, adjusting the infill pattern can influence the points at which infill connects to the walls. For complex shapes this might affect how successful the print is. There are also other parameters which you can adjust (overlap, orientation).

The 'best' infill settings are influenced by the requirements of infill, and the 'success' metric does not appear to have a sharp response that would be useful in performing an optimisation.

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I fear I'm going to deny your question. The infil percentage and the infil pattern are two orthogonal properties, both of which contribute to the strength, density, mass, and print time of an object. Since there's no way for an algo to "know" what your desired outcome is, this can't be done.

Note - I used 'orthogonal' in the Hilbert sense, meaning neither property is a function of the other.

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  • $\begingroup$ For some stupid reason (in my very newbie 3d printing brain), I was wondering if this wasn't the case. $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Aug 9 '18 at 16:22
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From what I can see, the only way to change the pattern is the manual way. There is still an open gate to create a plugin that could select the pattern - but that is rather a complex solution - unless you will have a fully automated pipeline

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There is a option for the infill pattern. It is one of the MAAAAANY by default hidden options in Cura. On the Header of the cathegories there will appear a gear symbol while hovering over the header. By klicking it a window will show up and provides this many options to be shown in the settings, if they were checked.

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  • $\begingroup$ True, and useful, but this doesn't qualify as "an algorithm to calculate a pattern" $\endgroup$ – Carl Witthoft Aug 9 '18 at 14:06
  • $\begingroup$ I'm honest that I'm not sure what exactly he wants, because an algorithm to choose the best infill will take really much cpu time and gets you nothing really useful without the information of the purpose of the 3d printed part. So I doesn't see this as the core of the question in first place. But if the question really want a algo to get the 'best' pattern: Nope, not without all information of the part, like force vectors and stuff like this. Because not 3D patterns (like grid) will have flaws against forces from the side. $\endgroup$ – Horitsu Aug 10 '18 at 5:20

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