Recalculating and flipping normals not working—but manually re-adding the faces does? (Simple mesh) See if you can help me figure out what’s going on with this basic chair geometry with normals issues.



I recalculate normals and—still have a normals problem.



I check the face orientation. Ok, a little mismatching.



I manually flip the normals but STILL the problem persists. (I tried both red and blue sides to be sure).



So I try an experiment: manually deleting the faces and re-adding them. I delete a face, select the adjacent edges and hit F to create a face.



Still a problem with normals.



I try this again but this time selecting all four edges before hitting F to creating a face. Fixed normals—and this works for all the faces. Can someone help me understand why this is?




Why are the Recalculate Normals and Flip Normals functions not working here?
Why must I select all four edges to create a working face? Selecting two edges is (technically) selecting all four vertices,is it not?
Obviously to go about deleting and re-adding every face is needlessly time-consuming to repeat across the entire mesh. How do I go about this correctly?


Thank you for your time,

John
The mesh has some inside faces, and Blender is confused by it :).  


Select the inside faces through Select > All by trait > Inside Faces
Delete them with X > Faces
Done.




Credits to @John for finding the best solution for his own problem :).