For best results using booleans:
- all objects should be manifold meshes
Note: Non-manifold meshes are only supported if the non-manifold components are not at the intersection of the boolean operation.
- face normals should be uniform across all surfaces
Tip: Before performing your boolean operation, view the normals on your mesh (Display > Polygons > Face Normals). If you want to produce predictable boolean results, make the normals uniform using Mesh Display > Conform.
- explicitly select objects for consistent results
Performing boolean operations on parent objects may produce undesirable results. If multiple meshes are grouped under a common parent, explicitly select the objects as input to the boolean operation.