Issue with Join

Why does this happen?

Join (11.1 MB)

However, when I try this before adding the semi tori, it all works just fine.

Join (6.4 MB)

I created the semi tori by first making a single torus. Boolean difference with the big object. Mirror semi torus twice. Boolean union with big object. The final result being:

looks like your normals may have flipped…try exploding the whole model and rejoining to see if it will fix automatically… if not, run “selbad” and see if the boolean created any bad objects. (typically a bad trim that can be fixed by un trimming and re trimming)

or go full nerd and explode and run the analyze direction tool to see which way the normals are pointing on each surface-

I don’t think that was the case. This is what I did. I started with this polysurface and trimmed it.

Which gave me this polysurface.

As you can see, I have given the “inside” of the model a different color. I do this for all my models, because that automatically shows me the direction of the normals. So I assume those were alright.

I then did Mirror twice, and Joined, which gave me that weird model in the first two images and the first video.

That worked! … But in a kind of weird way. When I explode this entire model:

I get this:

As you can see the normals flipped, and that weird indentation in the center of the model is no longer there. When I then do Join, everything seems fine again as I get this:

However, when I did Explode after the two Mirror, (but before joining the three parts), and then Join, it worked also and the model looked the way it was supposed to. Without the normals being flipped.

This makes no sense to me, since the only boolean I did was to connect the semi torus to the other part, and the normals all seemed to be pointing in the correct direction after that boolean union.

I don’t understand this. Why would this yield a different result if the “Direction” command on the complete model already shows that the normals are all pointing in the correct direction?

So I now know how to fix this when something like this happens again, and I would still like to have an explanation as to why this happened in the first place.

I went to art school, so the chances of me explaining why is zero… However I can tell you the way to fix it when it happens again is to explode and rejoin…if the model goes transparent on you that is a decent indication of a bad object that you can identify with “extractbadsrf” typically it’s a bad trim…If you untrim keeping trim curves, then fix the trim curve (look for gaps, overlaps, or cv’s piled up on top of each other) then retrim, often you can unbad it…

hope that helps-

Without the file we are just guessing…


Here is the file with just the three polysurfaces before I try to join. After Join it looks the same weird way as I posted before. Maybe just on my computer.

Join fail 01.3dm (643.7 KB)

However, … when I make a new file in which I show the steps of how I got to that polysurface before the final Join, this weird result does not happen. This is strange, and still keeps me wondering, why did this happen in the original file, but not in this new file.

Join fail 02.3dm (1.6 MB)

Hi Zews- I do not know what exactly is causing this to happen, but it appears to work if you select all three parts, Explode then Join.