How do I orientate an object exactly flat to a plane? I am building a turtle. With some boolean operators I'm cutting the plates on the back. I have to do this in place (round surface) especially because of boolean interaction.
Now I need the shields/plates alone, lying on the ground.
So I duplicate the shield-object, apply all modifiers, and seperate all plates by &quot;loose parts&quot;.
But now they are hanging skewed in space.
How can I align them exactly(!) to the ground?
(I'm doing it now by manually rotating in very hig resolution, but it allways remaines eye balled.)

Solved!!
   @Xtremity Sorry, I didn't read carefully enough first!
The clue was to go in edit mode, and select a FACE, not the object!
Now it works like charm! (Though a bit complicated, so I'll try to write (or find) a macro, as you told, because I'll have to do it many times.)
This is where it would be handy to have Maya's Bake Pivot Orientation command.  Sadly, I haven't been able to find a straightforward way to do this.  The best method I have come up with so far is as follows:


Set the mesh object's Origin to Geometry.
Create a custom Transform Orientation for the face you want to be considered 'up'

Create an Empty at the object's origin
With the Empty selected, use Object, Transform, Align to Transform Orientation
Parent the mesh object to the Empty

With the Empty selected, use Object, Clear, Rotation.  The mesh object's orientation will now be reset to 'normal'
Optionally, you can apply the rotation transform on the mesh object.