Hollow calibration cube without top - prints 'top'  

RE:

@walt_3d

No need to download a stl for that, just rightclick on the empty bed, "Add Shape" -> "Box", adjust size as you wish
In Print Settings, change Infill to 0, and Top and Bottom to 0, just as you did
Done 😀 

RE: Hollow calibration cube without top - prints 'top'

Thanks! Being relatively new to 3D printing and PrusaSlicer I didn't know that feature was there. Worked like a charm.

Still, it's puzzling why my original method doesn't work. Not that it really matters; just curious.

Just Guessing!!

@walt_3d

👍 😀 

I have no idea why it was not working for you 🤔

Tip for the future.
If, or rather when 😉, you have a question about a print, Save, Zip <- important, and upload the 3mf-file.
Then it will be much easier for forum members to answer questions
I can almost promise help will come running within minutes, within hours at most 👍 

Welcome and Good Luck

RE:

@Ringarn67

Thanks for the tip. In the context of better-late-than-never here is the zipped .3mf file. 

RE: Hollow calibration cube without top - prints 'top'

At least it says I am attaching a file, but I don't see it in the message. Does it show on your end?

RE: Hollow calibration cube without top - prints 'top'

Try again lol. 

RE: Hollow calibration cube without top - prints 'top'

OK, tried 'Attach file', now going for 'Add Media'

20mm_hollow_cube- open top.3mf

RE: Hollow calibration cube without top - prints 'top'

Now the correct one

20mm_hollow_cube- open top 2.3mf

RE: Hollow calibration cube without top - prints 'top'

I see now that we haver the model lol.

 I don't think you fully understand how slicing and 3d modelling works.  It can sometimes be a little hard to get your head around initially.  

Lets take a simple solid cube as a starting point.  From a 3d modelling perspective its what we call Manifold.  A manifold model is basically water tight.  In that if you filled the shape with water then none would leak out.  If the model wasn't manifold, like one of the edges wasn't connected to the edge next to it or it had a hole in the mesh leading to the interior then for that hypothetical shape water could leak out.  
Non manifold models can cause slicer problems. As the slicer can then have trouble determining what is the inside and outsode of a given volume/object.  Of course most slicers will attempt to 'fix' the issues and in many cases can.  With more complex geometry though then it sometimes cant or in other cases, the 'fix' it applies isnt what the original designer intended.  That why you see damaged models that when sliced you get holes filled in when the object looks like theres a hole there.

So the simple cube example, its got 6 outside faces and 6 inside faces.  When sliced those outside faces get Outer perimeters, then you get inner perimeters (if configured) and then of course infill to take up all the interior volume.  Simple so far right 🙂

Now we take your hollow cube.  Its a perfectly valid Manifold model, no errors and its water tight.  When you as a person look at it you see it has 6 exterior faces.  Wrong.  From a 3d model perspective it actually has 12 exterior faces.  The void in the middle has faces and technically those are the same as the ones you can physically see on the outside.  They are after all defining the void area.  The watertight volume is actually the space between this exterior shell and the voids shell.  From a model point of view the interior is this space between the 2 sets of walls.  If the size was large enough then the slicer would fill that area with extra perimeters and infill.  You will never get infill inside the hollow space. Its supposed to be hollow, that's what's been modelled.  

So now we come to vase mode.  Vase mode just tries to slice the external walls of a solid shape.  So with your already hollow cube its doing just that.  Its trying to slice all the 12 exterior faces of your 3d volume.

With a non hollow solid cube it does what you expect.  As I say it takes a bit of head space to get used to what actually happens with 3d models and slicing but you will pick it up.  You can actually use that to do some pretty cool things with vase mode.  Stuff like this https://www.printables.com/model/131488-spiral-vase-rose   which is a very clever use of it.  Or this https://www.thingiverse.com/thing:2277253   

RE: Hollow calibration cube without top - prints 'top'

@neophyl

Thank you very much for the explanation. I can see now how the slicer 'views'  and treats the internal volume as a water tight geometry. Makes sense. I compared my original model with sliced top and no infill, the shape-box with no top layers and no infill, and original model in vase mode. All different, and now it all makes sense.

Thanks again to @ringarn67 for the tip on the Shape-box. It was just what I was after. Led me also to the gallery, which I mean to explore further.