normals changed after separating object in 2 pieces When having smooth shading on a sphere and separating the top into a separate object the shading is no longer smooth over the 2 parts, there is a discontinuity:


It turns out the separate action changes the normals:


I understand blender recalculates the normals based on the mesh it knows within the object, but is there any way to override this behavior, so that on separation, the original normals from before the separate are retained?
Normal at a point P is a vector that is perpendicular to the tangent plane to that surface at P.

That means when you separate the mesh the Normal will be 90 degrees to the surface at the edges.

To fix that issue you can copy the original sphere and use it on both parts in a Normal Edit Modifier.