Cura closes open area

[ecka357 0]

Hello, i have tried to model plastic bottle like those which are sold in stores for drinking water. Bottle generally is modeled from three shapes:

almost square body with vertical rounded corners (1);

the top ring of the bottle with threads for the cap (2);

transition from the main square body to the top ring (3).

 

I have modeled the bottle with Autodesk Inventor, then converted the model to the STL file and imported it to Cura. Cura threw a warning after slicing that "Your model has missing or extraneous surfaces". Next the problem appeared that Cura sliced the "transition" part (3) and converted it to solid block where i need only the bottle wall to be printed. The other two shapes were sliced properly. Then i have tried to convert model to OBJ file, but sliced Gcode file also had the same problem. I have checked STL file in Windows 3D Viewer, the file was OK - i could clearly see that transition area is not filled. So this is the Cura problem. I am attaching STL and Gcode files, maybe someone will be able to help. Never had similar problem before.

 

When i send an STL file to Cura then bottle is

Bottle.gcode Bottle.stl

[ahoeben 1,951]

1 hour ago, ecka357 said:

Cura threw a warning after slicing that "Your model has missing or extraneous surfaces".

And Cura is right. Your model is non-manifold. Specifically the double-curved surface between the main body and the cylindrical top seems to have no thickness (and is inside-out). This makes the model unsuitable for 3d printing.

 

Being suitable for displaying the model and being suitable for 3d printing the model are two different things.

Edited March 3 by ahoeben

[ecka357 0]

This is strange, because Inventor shows decent thickness of transition shape (in light yellow color).

[Slashee_the_Cow 274]

What's shown in your modelling program and the STL file it produces aren't guaranteed to work just as well. A great running joke around here is SketchUp: it might look fine in that, but the STL files it produces are laughably terrible.

 

If you're on Windows, Microsoft's "3D Builder" app is actually really great. If you open your STL in that it offers to fix it if the STL has problems (which this one does).

[ahoeben 1,951]

I am sorry, I did not properly look at you model. You are right, the model does have an inner and outer wall. The problem is that the normals for the connecting loft are flipped AND that the loft has no caps and the two parts that it connects do have caps. So there is a single wall between the parts and the lofted connection, and that makes the model non-manifold.

 

However, in this case because the non-manifoldness is parallel to the slicing direction it is not a problem for Cura. It would be a problem if you wanted to print the bottle on its side.

 

Your model slices correctly in the orientation you have it now if you fix the normals. This can be done with the Mesh Tools plugin from the Marketplace.

[GregValiant 1,260]

304 naked edges and 4 planar holes.

Lofts are always tough because the math of the surface is so complex.  In addition, it is easy to get gaps between a loft and another feature.  They look merged, but they aren't.

This is what AHoeben is talking about.

 

Errors in a model seriously affect a slice.

 

 

Here is the transition between the lower rectangular shape and the transition loft.  Cura was unable to decide if they should be connected or not.

 

This model needs to go back into CAD and be repaired.  A couple of fillets at the transition wouldn't hurt.

 

When the loft is constrained to the other parts of the model, then the slice will be performed as you would expect.

 

[ecka357 0]

Thank you all for the answers. After many tries according to the given responses i was able to recreate transition shape in Inventor. Now i have used Loft function instead of Patch. After that Cura had not complained anymore and seems that sliced shape now is OK.

I have tried to use Loft function before but previously it did not worked. Then using the trial method i have created two lofts -one for inside and other for the outside, generating surfaces, not one solid block. Somehow inventor filled the space between those to surfaces.

[GregValiant 1,260]

Congratulations.  It will now hold more than a capful. 🍺

 

Loft and Shell are maybe the two trickiest functions to work with when you are trying to make a printable model.

A Shell feature needs to be in just in the right place in the feature tree.

Lofts from a square to a circle is tough math.  I will often break a circle into 4 arcs and add in extremely short lines between the arcs.  It still looks like a circle, but Inventor will see 4 sides to the square and match them up with the 4 arcs.  That will often eliminate any twists that might develop.

 

For threads I use my own thread form that has a 70° included angle because they don't require support.  Flat roots and thread ends are also helpful when printing.

Edited March 4 by GregValiant