Hi Michael,

> I want to merge f.e. 3 separate faces.
> I run the "merge"-command - the I selct the 3 faces -
> and then "enter".

Do you mean the Boolean merge command? The boolean commands are more for slicing up pieces that need to be intersected with one another.

If you have things that touch at common edges and don't need to be sliced up, then use the Edit > Join command rather than the boolean merge command to glue stuff like that together.

So probably in the case that you're describing there you would use Join, not boolean merge. If that's not right please post a 3DM file with your 3 surfaces in it so I can check them out.

Thanks,
- Michael