Cura error message - Again

[BruceR 0]

I am newer than a newbie to 3D printing. I have asked this question before but still having a problem with Cura telling me my model(s) are not watertight. I have attempted to use what was previously told to me with no sucess.  Yes. I have normal windows in my models but what models don't. I tried downloading a model from the internet from a respected designer but got the same 'watertight' error. Any suggestions from anyone. PLEASE

[GregValiant 989]

Consider a basic calibration cube.  It has 12 edges where one face meets an adjacent face.  There should be no gaps in those edges.  If there was a gap then if you tried too fill the cube with water it would run out onto the floor.  The model isn't watertight  (also called non-manifold).

 

When a slicer goes through the model it needs to know where the inside is and where the outside is.  That gap in a seam allows the slicer to move along the wall on the outside and keep going through the gap instead of onto the outside of the adjacent face.  Now the slicer is on the inside but doesn't know it.  That's when all the confusion jumps up and the slicing goes wrong.  That's why the warning comes up.

 

Even a "Respected Designer" is at the mercy of the software utility that converts a CAD model into an STL/OBJ/3mf file for use in the slicer.  Designers themselves can put a model together incorrectly and cause problems during the export to STL.

 

Cura has some basic STL repair functions (if the Mesh Tools plugin is loaded from the MarketPlace).  MS 3D Builder (in Windows) and Fusion 360 have decent repair tools as do some on-line sites (I've been using THIS ONE and it's pretty good.  I like the report it generates on what was wrong with the model.)

 

A pretty fair percentage of the problems attributed to Cura both here and on the Ultimaker Github site are actually problems with the models.  Of those problem models only a tiny percentage cannot be repaired without going back and fixing them in the CAD software.  That FormWare site I mentioned fixed one model that had 36,000 errors.  In that particular case I think magic was involved.