intersecting faces

Hi there,
I’m reworking the model from my previous thread:
http://www.blenderartists.org/forum/showthread.php?292338-spiral-like-object

Now trying to work with the knife project tool to cut two cylinders together, but I can’t get it to work well.
This is what it produces:



Am I doing something wrong?
Can it be done “precisely”?

Attached is a blend file with the three cylinders, and a sketch image of the goal.
knife.blend (584 KB)

Attachments


Guessing the problem was caused by the fact when in top view, the cut project object was 0 wide so using top face of the cylinder could produce much better result than the side faces.

Anyway, the result now I could make looks better, but cannot loop select all the faces at once.
Is there a way to resolve this?

Attachments

knife2.blend (522 KB)

Still things no good.
With right knife project objects, the result cannot be joined to a closed model.

How in the world to do this?



There are places where the cut gets right though, but mostly it doesn’t.

Attached is the blend file with the object to knife project,
and a result that I could make out of the previous.
Any help much appreciated.

Attachments

knife3.blend (743 KB)knife4.blend (633 KB)

As I couldn’t figure it out I went with the cylinder with the horizontal axis’s cut edge and reconstructed the faces of the vertical cylinder from the right vertexes.