# Creating a concave dodecahedron using geometry nodes

I'm trying to create concave dodecahedron using geometry nodes

I can create a dodecahedron

But how can I collapse the center vertices correctly?

That can be this:

Create the base shape as you did, using icosphere and dual mesh.

Extrude individual faces but with zero offset.

Scale this extrusion a bit to make final shape external 'borders'.

Extrude again, this time with (for instance) -0.5 so that the extrusion goes to inverted normals and near the center of the shape.

Scale this extrusion down to a small value.

Use subdivision surface with some edge crease amount.

As Gordon commented, you can harden the edges by adding a subdivide between last 'scale elements' and subdivision surface:

This will give:

• Okay, I actually like your solution better than mine ;) The only thing I would add because the reference image is tighter around the corner vertices and not rounded so much, is adding a Subdivide Mesh node between the last Scale Elements and the Subdivision Surface node, then play around with both Level values and the Edge Crease until you like the result. The edges will not be so smooth anymore but still have some "thickness" to it which looks good in my opinion. Commented Jan 2 at 8:13
• @GordonBrinkmann Yes, I've noticed that also. I'll add this to the answer. Commented Jan 2 at 8:15
• Playing around with the settings I found there are many options depending on which look you prefer. Without the Subdivide Mesh node for example setting the Subdivision Surface node to Level = 1 and Edge Crease to 0.4 or higher looks good when you add a Bevel modifier to the object. Or instead of beveling, just duplicate the Subdivision Surface node, leave the first at Level = 1 and set the second one to Level = 2 or higher. Commented Jan 2 at 8:31
• @GordonBrinkmann, yes, many possibilities... Commented Jan 2 at 8:41

Firstly, I have to admit this is not a perfect solution to get the result of the reference image you are showing, this deals only with the question how to select and collapse the center vertices.

To achieve this, you can use a Vertex Neighbor node and plug the Vertex Count output into a Compare node set to Greater Than > 4, because the center vertices have 5 neighbors. The result goes into the Selection of a Set Position node.

Then you need a Sample Index node to get the normals of the points. Scaling these with a Vector Math node by a negative value and plugging them into the Offset of the Set Position node will move the center points inwards.

The only problem with this method, I already added a Bevel modifier in the following image (or you could use a Subdivision Surface node in the GN modifier as well) to round off the sharp corners, but the outer edges are always pinching in the middle because of the beveled edges going towards the center. That's why my solution is not the best. Maybe someone else finds a better one.

//EDIT: And while I finished my answer, there already is a better one by @lemon ;)

The results in the other answer look strange to me. I would just merge the vertices after extruding the inset pentagons and use the bevel modifier. Yes, technically that is an additional modifier.

To add another piece to the palette of wonderful answers, here's another sharp-edged (and simple) approach that provides a useful topology:

Here I simply extrude the faces with $$0$$, then scale them a little to get a certain thickness, extrude them again and move their points to the center.

(Blender 4.0.2+)