Does it normal to make this copy for success to make a thickness of the middle face ?
If I just separate in place the Shell don't work!

Hi Pilou, can you please post the .3dm model file? If you're trying to shell the fillet that has some pretty tight curved areas in it that could be a problem.

- Michael

Very curious seems the fact of made the Shell like on the image
then some undos restart the good shelling!
So a new mystery! :)

http://moiscript.weebly.com/uploads/3/9/3/8/3938813/false_thickness.3dm

Hi Pilou, from what I can tell it seems that your first shell is successful but since it is to the interior of the object you cannot see it in your screencap above. If you hide the top piece then you can see it.

- Michael

A new one
I just make top/bottom Fillet
then try Shell middle face...fails...normal ... flip... center line

http://moiscript.weebly.com/uploads/3/9/3/8/3938813/false_thickness2.3dm

Edit! Ok That works only if this object is not a volume/solid but a "surface(s)"!
So effectively kill a face make the trick...but seems that must not be that normally!

When i have a cube i can take a face and make a Shell! ???

Hi Pilou, when shelling a solid and selecting a face to be the opening it usually has to have sharp edges all around it which yours does not because of the fillet.

The method used for shelling a solid with an opening is that the "side walls" of offsets around the opening are extended so they cut the face that is to be opened. When all the surrounding faces are smooth their extensions do not intersect the opening face and so that won't work for your case here.

A different method is used when thickening an open surface, in that case it generates an offset and then lofts between the open edges in the original and the offset.

So for your case yes you would want to delete the top face so that the surface thickening and lofting method will be used.

Here's an illustration for the solid thickening method, note that the face used as an opening does not completely disappear, there is a border remnant of it:





With your top face having smooth fillets all around it that "border remnant" will not be able to be constructed and so that's why your shell attempt did not work on that one.

- Michael

Thanks all is more clear now and explain why some things works or not!
That was not evident! :)
Hoppefuly there always another way to go (like above the "copy move") depending of the result wished...

In the same order of idea it's not obvious that the function "Extrude" can't extrude this ribbon face...
just some parts if they are trimmed...

Hi Pilou,

> In the same order of idea it's not obvious that the function "Extrude" can't extrude this ribbon face...
> just some parts if they are trimmed...

Well extrusion is something that actually happens to curves. When you extrude a surface what actually happens is all the edge curves of the surface are extruded and then the surface is copied to the end to make a cap.

Extrusion of curves works by translating the curve in a fixed direction.

What direction are you expecting to use for those curves such that they don't cross over and interfere with themselves making a "self-intersecting" result?

- Michael

There is a Joint Push Pull inside SketchUp who Extrude the curvated ribbon face above ;)

In Moi that will be the Shell...

As we can extrude these flat vertical faces ribbon (even they auto intersect during the extrusion) it's tempting to make the same with the curvating above! :)

Hi Pilou,

> There is a Joint Push Pull inside SketchUp who Extrude the curvated ribbon face above ;) <...>

SketchUp doesn't have actual curved surfaces, only flat polygons.


> As we can extrude these flat vertical faces ribbon (even they auto intersect during the extrusion)
> it's tempting to make the same with the curvating above! :)

If you divide the curved surface into flat pieces then an extrusion for each flat piece will be better defined.

Since MoI works on true curved spline surfaces there are different kinds of issues with possible self intersections.

- Michael