Boolean Difference fail (normals?)

Here is the link to my file --> http://pasteall.org/blend/index.php?id=49186
Software Version: Blender 2.76 (LinuxMint)

In the image below, I’m ABLE to cut a tubular hole through a simple generic mesh cube using boolean-difference. Good! However, I need to do several similar tube cut-throughs in an object called ‘shroud’. Bad - UNABLE to do this. Instead of a ‘difference’, the cylinder and shroud look more like a join after executing the command. Help?

BTW, I’ve read up on several threads here on blenderartists.org from members having similar ‘difference’ errors. They boards/posts have been helpful from a knowledge standpoint but they haven’t seemed to address my particular issue (eg. scale, remove doubles, redo the normals).

In closing, I’m wondering if the shape is too complex (Fgons? or Ggons? – not even sure what that language means yet) OR if the ‘inside’ box on the normalize action has something to do with it.

Thanks in advance for whatever guidance can be provided. Happy to research on my own (and will continue to do so while I await response(s)).

PS The cube with the tubular cut-through (right behind the central cursor/target) is what I’m trying to accomplish. TIA.


Object mode, shroud selected, ctrl+A -> scale to apply object scale.
Edit mode, select all, W -> remove doubles
Edit mode, select all, ctrl+N to make normals consistent and pointing out.
Always in that order.

The normals are facing the wrong way which is why boolean difference doesn’t give the expected result. Your model surface describes a everything in the universe as solid and it has a shroud shaped air pocket in it. It makes a boolean difference in that solid, that’s the result, and it is doing what it’s supposed to.


Boolean difference with inverted normals and you’re making an operation like on the left, but only looking at the inner surface. Normals pointing out and you get the result on the right.