Joining Objects Changes Shading

Hi, when I Ctrl + J to join all of my bottom objects as per 4:50 in the video I notice that the shading changes in the viewport. It didn't happen when the objects for the lid were joined. Any ideas as to what causes this?

https://imgur.com/0raFzMV

edit: changing the active object to one of the metal pieces prior to joining  helps a lot but there is still a minor change seen.

  • crew

    That's definitely a normals shading thing. On the joined version, all normals are set to smooth shading where in the non-joined version there were objects with flat shading.

    Ideally each object will be set to smooth shading with specific edges set to sharp. So if you go back to them being separate objects that are sharing object data, you can set to smooth and set the desired sharp edges, then combine.

    Sorry - I may not have been entirely clear about this, especially during the combination.