Why is there a gap in this blend?
I created the cutout not through a network but a blend which was later trimmed...

Hi niko - which gap are you talking about?

Are you talking about the "side walls" of the blend?

Blend creates a result that has no gaps between the created blend surface and the edges that you have picked to blend between.

The shape of the "side" parts of the blend is separate from that. Those come from a series of profiles that are created where each profile is coming perpendicular off of the edge.

- Michael

Hi niko, so notice if you view from an angle below you can see a bit more about how this surface's end is shaped:



Notice how its side edge is fairly slanted and is not actually perpendicular to its neighboring edges?



The Blend will create a surface that wants to be perpendicular to those edges meanwhile the other piece you have there is not set up like that, that's why they are not close to one another.

What you probably would want to do is to delete these 2 surfaces here:




And create blends in those spots to replace them, that way they will be shaped similarly to the blend you already have.

That's what I did in the attached 3DM file example, which looks like this:




- Michael

Yeah I knew how to make it seamless with your method, I just did not know why it behaved like that in the first place.
That pretty much explains it to avoid similar situations in the future.
Thanks