Hi jki,

re:
> For 3d printing I need perfect solid models.

If you need well formed solid models you will need to avoid certain arrangements of geometry that are self-intersecting.

The naked edges in your k1-joined surf.3dm file are at these shapes:







Here's a similar shape for illustration:



You don't want to have this type of arrangement where 2 cylinders just barely graze each other along an edge.

It's what is called a "non-manifold" edge where there are 4 surfaces meeting up at a shared edge. To have a perfect solid you need to have only 2 surfaces touching each other at a common edge.

The other thing that is bad about this type of arrangement is it makes for a very skinny thickness in this area:



It will be difficult for the 3D printer slicer to get a clean slice in such a thin area, instead of there being one clear path through that area it will be kind of a jumble of several possible neighbors within a small tolerance of each other.

That's something you basically just have to avoid doing. The pieces need to be either a little closer to each other so they don't just barely graze each other, or a little further apart so they don't touch.

- Michael