Nothing, you have run into another of sketchups issues. This is basically due to it having to make everything from flat faces and when you try to bend them it sort of makes flaps or overlaps.
When using follow me around a radius if the Profile Radius is bigger or very close to the same as the path radius you get these strange overlaps. The best option is to use a smaller radius than the path.
In this gif you can see from bottom to top 110mm, 100mm, 98mm and 90mm. 110 has some very strange overlaps, 100 has some very small overlaps, 98 almost works and can be repaired(tiny face issue again) and 90mm makes a nice clean sweep around the bend.
So there needs to be a bit of a compromise, although if you scale up further the 98mm will create faces and the difference in radius will be tiny at the correct size.
It is possible to make things work exactly, but it is easier to fudge a bit.
The native tools way to do this is to make a sphere and cut parts of it to use as corner parts. Fredo’s RoundCorner or FredoCorner plugins can also make clean corner fillets with equal radiuses.
But then , I do not know, if I missed something between of all your clarification, I selected the vertical face to close the top, I delete and sadely it did not work
You’ve probably got it from Dave’s gif but I made this so here it is.
You need to look at the hidden geometry to understand what is happening.
You can see in the gif if I draw an edge out from the end of the arc the next segment is angled down, so if you select that edge and delete it it will delete the first part of the arc because they are two different faces, but having a straight section between the arc and the end of the profile it allows you to select and delete without touching the edge of the arc.
Look carefully at the hidden geometry.
I did not move the profile out the path, because the result will be larger than 1000mm.
My goal is to decrease 1000m and 40m(thinkness) to 100mm and 4mm.
Here is how I could make (because of you:).
My box has a vertical radius of 100mm
The top (profile) has profile of 90mm
Yesterday, @Box suggested to extand my profile. It was I just did, but I extend it of 5mm (instead of 10mm)
Just to confuse you now that you have got that method, here is another version to show there are always other options and issues.
Once again you need the arcs to be appropriate.
By have the profile be half the overall size you get two crossed faces, and when the profile is touching the path face you don’t get the warning message but you can see it removes the face where it follows the path.
So all the bits and pieces we have been through in this thread can be used in whatever way works best for the shape you need.
