Boolean difference modifier creating artefacts I am trying to make hollow cube something like this:


I am new to blender but I would have thought that this should be straightforward. I made a cube, and then a longer cuboid which I inserted in the middle and then used the Boolean difference modifier. I changed the orientation of the cuboid twice more to make the other two 'holes' through the object.

Since the operation seemed to go smoothly, I was surprised to see that the holes didn't cut right through the cube, and that in wireframe mode some artefacts were created:




I tried making both objects solid (using the solidify modifier with default settings), but even after making the first Boolean difference operation I can see an unexpected triangle in the model:

 

Could someone please advise me on what I'm doing wrong?

I am aware that for a simple model like this I could assemble it from cuboids, rather than using a difference operation. However, I would like to be eventually use the techniques to make more complex models for instance a hollow Dodecahedron. Therefore I keen to establish the correct way of making these hollow type models. 

I am tempted to try making a new face for each side of the cube and extruding it inwards but I don't know how I would handle getting the inwards extrusions to join up with each other.
Option A subdivide all faces of a cube, select the middle edges then bevel them. Either extrude the large faces inwards, or erase them and use a Solidify Modifier. If the former don't forget to remove doubles.



Option B Just select all fates then use Inset > Individual Faces then *Extrude > Region (Vertex Normals).



Also works in icospheres. If self intersections are not a concern you can use a Solidify Modifier replacing the last extrude step.



Alternatively you can use a Wireframe modifier, for a slightly different geometry.