Create solid from copied elements

 From:  MAT13
11789.1 
Hello
I've had MoI for a while, never really used it too much.. (Modo/Blender)
I'm getting into 3D printing now, so upgraded to v4 and have been testing it again, following online tutorials.. But I still need some help with some basic understanding of the workflow I guesss..
There's something I can't get to work properly, which is to create new solids from copied elements.. I'm not sure i understand the difference ebetween the commands "Join" and "Merge", but in any case none of them work in this - I thought - simple example:
I copied the two surfaces from the base solid, joined the top edges with the planar tool, but impossible to do the bottom, I get many surfaces covering the whole circle.. In ther occurences I was able to to that, but impossible to make it a solid.. Is that not a valid method ?
(see screenshot and attached 3dm file)
Many thanks in advance..