Boolean union deletes some faces


I’m having trouble using the boolean union in blender.
I start by creating two NURBS curves and increasing their Bevel depth value. That gives me image [1] below. Then I convert both curves into meshes and Remove Doubles to get image [2] below but after converting faces to triangles and recalculating normals it looks like image [1] again. But then I take the boolean union and erase the original meshes and am left with image [3].

Some things I don’t understand and would appreciate an answer to:

  • Why does a mesh created from a curve have so many double vertices that I need to remove afterwards?
  • Why aren’t the normals all pointing outwards on the mesh created from a curve?
  • What are the black edges on image [2]?

And most importantly:
Why did half my object disappear when I took the boolean union?

Thanks in advance!

I did a small test, converted unedited ( besides bev depth and res ) beizer and nurbs and got no extra vertices and all normals are the same . Must be something your doing. The black edges are where 2 connecting faces do not have the normals facing the same. Are you using 2.49 ? I don’t see many of the normal tools here in 2.53 I never did boolean with triangles, ill give it a try

What do you wish to do with the boolen ? When i did union I get the two united to one and a extra part