Hi Franz,

> I saw that I have to use a different tecnique depending on the case. If one fails the other one works. See the image.

Really either method should work, just as long as you have constructed a result that does fully intersect the other object.

If you want some more feedback on the ones that don't work, could you please post a 3DM file with the objects in them so I can test over here and see what's going on?

One tip - it can be easiest to make sure your cutting object extends a bit past just the outer surface of the object to be cut, that way you can be sure that it actually fully divides the object where it cuts into it.

- Michael