STL repair tools outside of the computer graphics software tools such as Blender

General Discussion
1

perhaps i am just lazy or just dont want to put out the effort to learn Blender, FreeCad and the like …
i read somewhere, seemingly authoritative, that the process those programs use to export STL files had common flaws that the actual slice process didnt detect nor correct;

my tools are :
Prusa Slicer 2.6.1
Prusa Slicer 2.7.1
Ultimaker Cura 5.6.0
AutoDesk Meshmixer 3.5.474

why both versions of Prusa you ask ?
2.6.1 has a “fix with Netfabb” option; 2.7.1 replaced that with ‘fix by repair windows algorithm’ ( note that replacement is in the exact same place in the menu options as the netfabb previous option );
what i found was that if i send a newly gained STL to Prusa First i get the best results at the end of the ‘repair chain’;
Prusa has some error-checking at Import time ( as well as reporting what it found and what was yet to do; that is missing in the other tools );
then prusa has the menu ( right click) options mentioned above;
i read somewhere that Fixfabb is quite an operation, highly respected German company;
until recently i think they had a free online service ( maybe that is what prusa was actually using);
after the 2 steps regarding prusa, i export then and send to meshmixer (“MM”) to use it’s Inspector tool (under Analyze menu);
i tried reversing meshmixer and prusa and i found that on occasion MM would just tear up a model on it’s attempt to Inspect and fix it; so i inserted prusa as the initial step;
i have on occasion seen MM catch and fix errors that prusa didnt;
after all that i export and send to cura, cura has an initial import check for water-tightness as well as mesh tools;
after an export there, i send to Bambu Studio; it seems Bambu error checking is only done at slice step;
just today i went thru my normal, Prusa, MM ( okk i did skip the cura step today…);
then slicing in Bambu showed an empty layer error !!
how could that have gotten by the prior error-checking ?
inspecting the model closely in MM ( which i think has the best visual checking) i could see the open layer; ( i suppose a cura slice could have shown that empty layer);
does anyone have their own system which they trust ?

2

What you are seeing is why I try to separate repair from validation. A slicer can accept a mesh and still produce an empty layer later.

My usual preflight is:

  1. Keep the original STL and make a repaired copy. Compare the bounding box before and after every automatic repair.
  2. Check one known dimension before trusting the scale. STL has no reliable unit field, so an inch export can look like a 25.4x size error.
  3. Check for open boundaries, flipped or self-intersecting triangles, very coarse facets, and disconnected shells. “Watertight” is not the same as “correctly sized”.
  4. Slice the repaired copy through the suspicious Z range. Empty layers often expose a local gap or self-intersection that a general import warning did not catch.
  5. If the part came from CAD, ask for STEP as well. STL is a triangle approximation, so it cannot preserve exact faces or hole semantics.

For a quick first pass before sending the file through several repair tools, I use the CADProps STL viewer to inspect the mesh dimensions, pick point-to-point distances, and see whether approximate closed-mesh properties are available. It is a preflight check, not a repair engine or manufacturing validation; files are uploaded for server processing and the measurements remain approximate for mesh geometry.

I’m working on CADProps, so that link is a project-related reference rather than an independent recommendation.

3

The point about separating repair from validation is the part I keep coming back to. Your chain relies on each tool’s automatic fix, and the import warnings in Prusa don’t guarantee the repaired copy is dimensionally correct. Comparing bounding boxes before and after and checking one known dimension would catch a scale issue that a watertightness check won’t. Slice through the suspicious Z range is a practical way to confirm a local gap the inspector didn’t flag. Asking for STEP alongside STL also makes sense when the source is CAD, since the triangle approximation loses face and hole semantics anyway.