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Best way to partition interior of part?


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Posted · Best way to partition interior of part?



I'm just learning Cura and have a question about defining walls within the interior of a model. My naive approach was to do this with per-model infill settings, where one model in completely enclosed within the other and used to locally modify the infill density to 100%. This seems to work, but there are many switches and knobs available that I still don't know anything about - is there a better way?


For example, the attached model is a simple cube with a tube curving through it...what's the best way to make the walls of the tube solid so as to form an interior passage? What settings are most relevant for this sort of thing?


Note that I am not particularly concerned with the printability of this example. Right now, I'm just focused on learning how to use Cura itself.





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    Posted · Best way to partition interior of part?

    Usually it's best to model interior spaces using your cad software.  For example in CAD one can create a cubic void inside a cube.

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    Posted · Best way to partition interior of part?


    That sounds logical to me, but I still don't get how to then use Cura to produce the actual part I want.


    I have CAD models of both the cube and the tube. For the example I posted, I imported these as separate files into Cura so I could control their settings individually. Then, within Cura, I combined them using 'Merge Models'. That's the only way I know how to generate the model I posted and I want to know if there's a better way.


    I could certainly use my CAD software to combine the cube and tube into one part/file, and then import that into Cura. What I don't understand is how I would then tell Cura that I want 100% infill for the walls of the tube and 20% everywhere else within the volume of the surrounding cube.


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    Posted (edited) · Best way to partition interior of part?


    I just found some new information that seems to agree with the example I shared. That gives me the confidence to proceed with the CAD work I need to do to prepare my actual model.


    I'd still like to hear about any other approaches, caveats, related settings, etc.


    If it's helpful, here are the references I found on this topic...


    I based my first attempt on this helpful video -


    I then played around with Cura to create the example I shared.


    I also went looking for related discussions and, at first, I didn't find anything of interest. Since posting this question, I found this valuable discussion with additional details - https://3dprinting.stackexchange.com/questions/6522/different-infill-in-the-same-part . That post actually links back to a discussion here -



    Edited by noodler11
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    Posted · Best way to partition interior of part?

    Hi @noodler11, welcome to the world of 3D printing! I am responding to this on a tablet so I am basing this on your text description.


    When you create a model in CAD like a cube with a tube through it, the model created has an “inside” and “outside”. The boundary between inside and outside is described by the mesh of triangles in the STL file. What you think of as the open inside of the tube is part of the “outside” as far as the model is considered. This is often accomplished by subtracting one shape from another, or performing an extruded cut.


    Cura treats the surface of the mesh as the “skin” of the model. The skin is referred to in the settings a number of ways depending on orientation, but includes walls (vertical) and the top & bottom layers (horizontal). The settings referencing “skin” specifically affect the outer loop of a wall (or the inside loop of a hole—i.e. the loop with plastic on one side and air on the other).


    What this means is that it is not necessary in most cases to have different infill settings to describe a void. This works even with completely enclosed voids. Imagine a 30mm cube with a 10mm cube void in the center. If you look at the cross section of the middle, you would have a 10mm thick wall surrounding a 10mm space. For this example, I’m using a 0.5 mm line width to make the numbers easy. The typical settings have walls 3 lines wide. So the outermost 1.5mm is considered “wall”—with the outermost 0.5 of that considered “skin”. The next 7mm are infill. And then there are 3 more lines (1.5 mm) of wall to define the hole. The settings for infill only apply to the 7mm section.


    When you “slice” a model in Cura, it analyzes horizontal cross sections separated by the thickness of the layer and then figures out what parts of that 2d layer is skin, other walls, infill, etc. It also takes into account the layers below for figuring out things like bridging and overhangs. After a slice is complete, you can examine each of the layers in the preview mode using the vertical slider at the right of the screen.


    The last example to which you referred is an unusual situation.

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    Posted · Best way to partition interior of part?

    Hi @johnse,


    Your 30mm cube example with numbers really helps clarify how Cura "sees" these settings - thanks!


    I'd be interested in any references which provide similarly analytical explanations of the various Cura terms/settings and how they relate to each other, especially with diagrams (apologies if I missed that in the documentation).


    Let me apply my specific case to your example - a 30 mm cube with a 10mm cube void in the center, with 1.5mm walls. Suppose my tubular passage through the cube is 1mm in diameter. What I want is to set the walls of that tube to be 1.5mm thick and the remaining (non-tube) part of the outer wall to be 3mm thick.


    The example I shared uses variable infill to achieve this...although, for that example the non-tube wall thickness is actually set to 0. Is there a better way to do it?


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