Shade Smooth and Auto-Smooth problem when combining objects So I'm making a catapult and I need all the parts of the arm joined together so when I animate it, they all move together.



The problem is when I join up the parts of the basket and arms in the front together, the shading gets messed up because the arms are shaded smooth with auto-smoothing and the chain link has been shaded smooth without auto-smoothing isn't. Refer to images below.



How do I make it so that both the chain and the arms retain their individual smoothing settings or combine them in such a way that both look good?
Solution 01
Smooth/flat shading is applied per face, not per object.
So just change it for individual faces of your mesh.  

Here is an example of a chain.
It's one object, consisting of multiple meshes, like in your case.  

Select only one mesh.
Click a face and then Select->Select Linked->Linked


Apply shading only to these faces.
Mesh->Shading->Smooth faces


You're done.
Different parts of your object are now shaded differently.


Solution 02
Play with the Auto-smooth angle.
Auto-smooth is applied per the whole object, but you can adjust what edges are considered smooth.


Solution 02.1
(thanks to Robin Betts)
Mark some edges as sharp.
They will then be shaded flat, no matter what the angle is.
Edge->Mark Sharp.