Failing to get settings right for hollow no top/no bottom

[righdforsa 0]

Hi, I am trying to create a resonator object to play with, but am having no success getting the slicer output settings to produce the part that I've designed. I'm getting the "missing or extraneous surfaces" error, whether I use the version of the part where I have "thickened" the surface, or just with the raw surface. (Mesh tools says it's not watertight, but that's not a surprise, it's not supposed to be enclosed to begin with.)

 

I prepared the model on Onshape, and my suspicion is that I have intersecting faces sharing an edge, though I've tried to union all the pieces together before exporting the STL. The end result I'm looking for is solid walls, (i.e. with no infill, approx. 2-5mm thickness, this is just a first pass so I don't have a precise specification for the wall thickness) with no infill in the cavity, no top, and no bottom. Help!

 

 

helmholtz resonator.stl

Edited February 7, 2023 by righdforsa

[GregValiant 1,251]

"Water-Tight" around here means that there aren't any open seams in a model.  The model can have lots of holes in it.

Here is the bottom of your model in Cura (Mesh Mixer shows the same sort of thing):

Cura is using the polka-dot coloring to indicate errors in the model.

Here is a report on your model from formware.co STL repair site.

-> Analysed your file:
--> 16 Naked edges (?)
--> 0 Planar holes (?)
--> 0 Non-planar holes (?)
--> 50812 Non-manifold edges (?)
--> 34415 Inverted faces (?)
--> 0 Degenerate faces (?)
--> 66912 Duplicate faces (?)
--> 0 Disjoint shells (?)
-> Repairing: 100.00%
----- Repair completed in 8330ms ------
-> Vertex count changed from 36352 to 35856 (-496)
-> Triangle count changed from 107136 to 71712 (-35424)

I would call 50812 non-manifold edges fairly porous.

 

The model attached below was repaired by the formware site.  It still won't hold water, but it's "Watertight".  MS 3D Builder was able to repair it as well.

 

 

That will result in this.  Spheres are hard to print without infill or interior support of some kind.

 

helmholtz resonator_fixed.stl

Edited February 8, 2023 by GregValiant

[righdforsa 0]

Thank you so much for your help! Can you clue me in on why a spherical surface creates non-manifold edges?

> Spheres are hard to print without infill or interior support of some kind.
Oh, that makes sense, I'll see what I can figure out. 

[GregValiant 1,251]

The report says there were 50,812 non-manifold edges.  I think there was one error that covered the entire interior of the model.

If you subtracted a smaller sphere from the inside of the main sphere to create a hollow ball, it looks like the entire inside surface ended up being a mess.  Consider the number of "duplicate" faces and the number of "inverted" faces.  Something went completely sideways when the ball was hollowed out.

 

So to answer your questions of " ....why a spherical surface creates non-manifold edges?"  They don't.

The CAD software appears to have made a hash of the subtraction (or revolution, or however else you did it).

I don't know OnShape but I think you should consider looking at different CAD software.  Some are certainly better than others at creating "good" models for 3D printing.  There is a learning curve involved in all of them.  Autodesk's Fusion 360 seems to be pretty good and it has a large following, and there are a couple of others.  Maybe @gr5 could suggest something.

I run an old version of AutoCad Inventor called Mechanical Desktop.  It's still an excellent assembly and parametric modeler.  Finding good 32 bit computers that will run it is getting tough.

 

 

[geert_2 557]

In case of a cube, you could think of "watertight" as it being one chunk of solid metal. However, if that cube is made of six cardboard sheets glued together, with seems and gaps between the edges, then it is "not watertight". In old computer games you often see such gaps between walls, where the edges do not lign-up correctly, so these models are not watertight. Models made with SketchUp usually are not watertight either, because that program was originally made to design visual 3D-buildings for Google Earth, not for 3D-printing. For 3D-printing you need a true solids modeler.

 

[gr5 2,172]

I'm sure on shape is okay.  Just Google manifold on shape and learn how to be sure your models are manifold.