"Joining" points in one mesh

Question

Given: a mesh which forms one-n'th of a torus. I Alt-D-duplicate it, rotate the copy by 360°/n, and get the ends to meet up. Repeat n-1 times.

I have now a nicely symmetric object which I can edit further. This is not the problem.

The problem is that when I move a vertex at the border between copies, that nice alignment is destroyed. Obviously I cannot join the corresponding vertices; it's the same underlying mesh, after all..

Thus, how can I keep them in sync while editing? Repeating the edit steps on the "other" side is tedious, and snap-to-vertex doesn't help much either.

To clarify: I want to create a closed object with n-fold symmetry which stays closed and symmetric, no matter which vertex/edge/face I move. A normal torus will not stay symmetric. A 1/nth-torus with n-1 360°/n-rotated copies will not stay closed when I move a vertex/edge/face at the border.

Answer 1

You could merge the vertices by invoking the Remove Doubles operator

In your case you could create the torus without duplicated vertices, starting with an e.g. an 1/8th

By rotating using the Spin Tool Alt-R in Edit Mode

Answer 2

I don't completely understand the problem you are encountering, but here are a few things you might try:

1. While in Edit mode, before you start modeling (such as duplicating your torus sections) turn on "Automatically merge vertices moved to the same location":

   

   This makes sure you won't have double, non-merged vertices in the same spot, thus you won't have to use Remove Doubles later on.

2. When you use ALTD to duplicate the torus section, you are creating what is called a Linked Duplicate. With Linked Duplicates, whenever you modify the section, ALL of the sections will be effected, as shown here:

   

   However, if you don't want this to happen, use SHIFTD to create non-linked Duplicates. With these kinds of Duplicates, when you edit one, the others remain unedited, as shown here:

   

If you want to learn more about the differences between Duplicates and Linked Duplicates, you can read more about them here: http://wiki.blender.org/index.php/Doc:2.6/Manual/Modeling/Objects/Duplication

Answer 3

Try using an Array modifier:

1. Add a torus and delete three quarters of it:

   

2. Add an empty and rotate it 90° around the Z (or whatever axis to which the torus is aligned)

   

3. Add an array modifier to the torus, with Object offset enabled and the empty selected as the offset object:

   

By using the 3D cursor as the pivot point and being suitably careful about how you move your vertices maintaining a manifold mesh shouldn't be too hard. Another advantage to the array modifier is that it updates in edit mode.