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I created a grid (as multiple curve paths) which is in and outside of a sphere. When I'm trying to delete all parts outside with the Boolean Modifier, it says "Cannot execute boolean operation". How can I solve this?

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  • $\begingroup$ The Boolean modifier most likely will fail dealing with intersecting geometry, like one on intersections of the grid lines, see blender.stackexchange.com/questions/5140/…. It might be necessary to delete that intersecting geometry of grid before executing Boolean which can be quite cumbersome task. $\endgroup$ – Mr Zak Mar 3 '16 at 11:40
  • $\begingroup$ I created a extra topic with this problem: blender.stackexchange.com/questions/48159/… $\endgroup$ – Basti Mar 3 '16 at 13:32
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The problem is, that you need a proper (non-manifold) mesh to do the Boolean operations with. The method you used to create your "Grid Cube" doesn't help here because it doesn't prouce one. You could check your mesh in Edit Mode hitting Ctrl Shift Alt M with the Mesh Select Mode set to Edge or Vertex.

Here's a better Method to create your Grid-Frame-Cube:

  1. Create a small cube in the corner
    • Add a default Cube (2x2x2) in the Center and name it miniCube
    • Position your 3D Cursor to the front bottom left corner by selecting the Vertex in Edit Mode and use Shift S, Cursor to selected
    • Pivot around the 3D Cursor and scale your Cube (S) by 0.25.
  2. Duplicate this small cube twice, name one Grid and one inner, then hide the original miniCube or move it to another Layer as a Backup. You might need it later again to play around with the following Bevel settings.
  3. Select the inner Cube and in Edit Mode select every Vertex (A), then use an Edge Bevel (Ctrl B) of 0.25.
  4. Select the Grid Cube and add a Boolean Modifier with the inner Cube as Object in Difference mode. (This will cut out the inner part, basically only leaving the grid-frame)
  5. Add three Array Modifiers, one for each Axis to the Grid Cube. This basically creates the grid-frame-like Cube structure you created but with a proper geometry.
    • Set the Count to 4
    • Set the Relative Offset to 0.0 on each but 1.0 for one axis: x for the first Modifier, y for the second and z for the third.
    • Check Merge

Now you can add the Boolean Modifier to the 2x2x2 Sphere in your Center with an Intersect Operation and the Grid as its Object and it will work fine:

Sphere intersected with Grid Cube

You could of course play with the Bevel of your small cube before to get your grid nicer looking. You could use more Segments or change the Profile from 0.5 which is "flat" to a smaller number like 0.25 to get a more rounded grid-frame. Its settings are available in the panel in the Toolbar once you confirm the Bevel before doing any other operation or by hitting F6.

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