Shading issue on instances by vertices

Question

I am making some railings and instead of use the array modifier to repeat them, I choose to do it using instances by object's vertices.

My problem is at the point where instances connect. I have this ugly line between them...

Any idea how can I make connections look smooth?

UPDATE #1

And here is my initial mesh...

UPDATE #2

Hard to tell without seeing your mesh. Does this answer your question? How to approach the modeling of duct work, piping, wiring? — brockmann, Mar 04 '21 at 13:09
Related: https://blender.stackexchange.com/questions/27383/join-two-cylinders — brockmann, Mar 04 '21 at 13:11
A wireframe would be helpful. Anyway, you would have to find a way to merge the verts, or cut the object in the middle, otherwise you get doubles hence the shading issue. Have a look into the first link how to get proper topology. — brockmann, Mar 04 '21 at 13:59
You won't get that solved with instances, at least not with this mesh. Instead of creating two vertical half-pieces at each end, I'd go with one full pipe at one end. — metaphor_set, Mar 04 '21 at 16:01
@metaphor_set I have to use instances so to keep vertices, edges, faces and triangles low. Take a look at my second update. — Simos Sigma, Mar 05 '21 at 08:07

score 1 · Accepted Answer · answered Mar 05 '21 at 16:03

A file would be nice, so that we could be sure we were giving proper advice. But what it sounds like is that you have geometry that acts connected between instanced objects, but the normals are discontinuous between the geometry.

Let's look at a cylinder. When you split the cylinder in half, into two different half-cylinders, it's just like marking the midline edges as sharp. In the full cylinder, these edges' vertices compute their normals from faces wrapping around the entire cylinder, but in the half cylinder, these vertices aren't using the same faces to compute their normals-- they only know about half the faces. We can see the dividing line when comparing our whole cylinder to our two half-cylinders below:

So how can we can get the edge vertices to act as if they're part of an entire cylinder? By giving them custom normals, copied from a whole version, with a data transfer modifier.

Because of the method (nearest corner of nearest face) we need to use the data transfer when the meshes are all in the same place, which is hard to show in a single picture. When the normals are correct, we should apply the modifier; after that, we can delete the target mesh. Custom normals require autosmooth to be enabled (but it will ignore the autosmooth angle once the geometry has custom normals.)

Shading issue on instances by vertices

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