Hi Bence, how was the knife grip created? Some areas of it seem to have surfaces that are not touching very accurately even though they have a joined edge between them.

I found this by examining some of the intersection curves generated by Construct > Curve > Isect. Some of the intersection curves are not closed curves, there is a little bit of space between them like this one:



I separated out the surfaces around there and untrimmed them to get an idea of what the underlying surfaces look like, and there is a little bit of space between them right where you see the separation in the intersection curves:



It's a small distance, like just below 0.001 units. Normally things that are apart by that distance are ok to be glued together but in your case here it seems to be too close to the size of the sphere.

- Michael

I would look for where three seems cross. if you find that case, spin the ball so the seem of it is away from the crossed seem in the handle. that would be how I narrow things down.

Hi Bence, here's a version with the booleans completed.

I scaled it up by 10x in size and sort of un-striped it by using Boolean Union on pieces that had been cut from the same original surface and used Construct > Network to build this area:



Then booleans went ok after that.

- Michael

Michael,you are a magician, I still have to learn a lot I see, kind of a beginner, thank you <3