Duplicating surface of cube adds a circle to it

Question

I have recently started learning 3D modelling in Blender and I am making model of a Rubik's Cube.

Here is what I have done:

1. Added Bevel and Subdivision Surface to the default cube for smoothing its edges.

2. Duplicated one face of cube so that I can color it.

But when I duplicate the face it gives me a circle on top of that side instead of exactly duplicating the face. What am I doing wrong?

Here is what I am getting:

EDIT: I am duplicating the face because I want to keep the grey boundary while apply the material in central area. I solved the problem mentioned above by adding 4 loop cuts to the face. But when I apply color on faces they all appear kinda jittery when I rotate the cube. Can anyone tell me why is that so?

Answer 1

This is because when you duplicate the face, it is now a flat plane and the subdivision surface modifier is treating it as a separate mesh and rounding it.

To get around this, you can disable or hide the modifier while working by clicking the eye icon on the Subsurf modifier.

If I also understand what you are trying to do, it's also worth noting that you don't need to duplicate the face to apply a material to it or to modify it specifically. Objects can have multiple materials in Blender. You can go to the material tab, select a specific face, add a new material and apply it specifically to that face by clicking Assign.

Answer 2

If all you want to do is to color the face you can do that directly in the mesh without having to create a new one. Here is how: In edit mode select the polygon you want to give a different color. Go tot the material properties. . Then add a new material(1). Note if you did not create one for the base already do that first. With the polygon selected click 'Assign'(2). That is it. From here you can change the color (4) and give it a proper name(3).

---

If You just want to fix the geometry you can also first duplicate the mesh and place it right with the original and then you can select the face you want to keep and go out of edit mode and apply you modifiers. Then back into edit mode 'select inverse' (Ctrl+i) and delete(x) the vertices.

Duplicate the mesh in place

Duplicate mesh appears in outliner

Select the face you want to keep

Apply modifiers in object mode

back in edit mode you will see your selected face. Hit Ctrl+i (select inverse)

Delete the faces

Final result

---

The jittering is because of the overlapping faces.basically blender has two things in the same place and blender does not know which one to show. (just like in real life two things can't be in the same spot)

Answer 3

There's a good link here that explains the Catmull-Clark subdivision algorithm that's being used when you add a subsurf modifier: http://www.idav.ucdavis.edu/education/CAGDNotes/Catmull-Clark/Catmull-Clark.html