I want to create an invisible door in a sphere that has been shaded smooth. But when I select some vertices from the sphere and do rip vertices to them (without move vertices) I have a trace on the sphere that shows placement of my door.
As @Hikariztw has suggested, you need to give the cut sphere some custom normals.
- On the cut sphere, check 'Auto Smooth' in its Data tab > 'Normals' panel, to enable vertex-per-face normals
- Retain an intact copy of the sphere, in exactly the same place as the cut one. You can M,move that to another collection, and hide it, to avoid confusion. I've called mine 'Form'.
- Give the cut sphere a Data Transfer modifier, settings as shown, to copy the normals from the intact sphere to the cut one.
You can apply the modifier, and dispose of the intact sphere to tidy up, if you like.
EDIT: in 2.8, you can evaluate the normals in Object space by unchecking the little collection icon at the right of the 'Source Object' field. That way, the target 'Form' does not have to be in exactly the same location or orientation as the cut sphere.. you can just shove it off to one side.