Multiple components to STL have shell walls between components

[AubsUK]

I've been struggling to work out how to export multiple components to STL, and I hope someone can help me.  I've searched extensively online and the only results come up with how to export multiple components, but none appear to relate to the inner shell walls.

If I turn on only the components I want, then export Save As STL from the FileName at the top of the browser, import to Cura, I get the first image, which has inner shell walls between each component. As you can see where the 'Play' button is from Cura, there is an overlap of the wall which creates a bulge in the printed piece.

If I merge the components to a single new component and Save As STL, it all looks as one piece with the infill correcly flowing between components and only a single outer wall where there should be one.

Any assistance to point me in the right direction would be appreciated.

2.0.9937
Active Plan: Fusion 360, Personal
Windows 10 (19041)

Ultimaker Cura Version 4.8.0

[etfrench]

Without the file, it's a guessing game.  File/Export/Archive file *.f3d and attach the output to the thread.

[AubsUK]

Sorry for not including it.  I've replicated it with a simple sketch and attached to this post.  I've also attached the STL two files.

[etfrench · Accepted solution]

It's your slicer, not Fusion 360.  Check Cura settings to see if it has any options on how to handle multiple bodies.  I have Cura, but don't use it. Prusa Slicer works better for me.  It handles multiple bodies the way your are expecting.  The screencast shows how it handles your two stl's as well as one I created.

[etfrench]

If the screencast doesn't show in the last post, here's the link: https://knowledge.autodesk.com/community/screencast/f9e2c514-1ef1-4163-a0b2-e8d6c42fc622

[AubsUK]

Thank you for taking the time to post the screencast and advice @etfrench, that's exactly how it should look.

I've asked the question on the Cura community forum and will see what responses I get.  I'll report back here for completeness once I have an answer (my post needs moderating as it's my first!).

Link:

community.ultimaker.com >> Multiple joined components in one STL generate shell walls between compon... 

[AubsUK]

A response on the thread I posted in my last comment said the following:

It's not the slicer really. If you don't combine the parts, there will be a surface between the two objects. Since STL doesn't actually define what is inside or outside (it only defines surfaces) you get weird results like that.

As you can see, there is a small gab between the two objects. This gap is caused by the tessalation (eg; It needs to create flat surfaces, so a round surface is approximated by multiple flat ones). This process will pretty much always introduce inaccuracies, which can lead to gaps like this.

The result that you see is basicly your slicer doing exactly what you ask it to do; There are two components and they are printed as two components.

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I've tried the test and my original multi-compnent STL in PrusaSlicer and both do exactly as you said.  I can see that PrusaSlicer is multi-compnent aware, so slices them as one where there's overlap.