 I want to make a 3D printed sphere made of 20 triangular pieces.
 I have started with a sphere 25 cm radius, added an icosahedron with the vertices touching the sphere.
 I select a triangle and project it onto the sphere.
 Delete everything else.
 Extrude the surface 2mm.
 Help: I need to close the two surfaces to print 3D.
Note: Instead of showing you what I did, I prefer that you follow the steps 25 yourself. When I try to do it now, I obtain 3 curves, not a surface.
I’m referring to this: 2525.4.
I made this other piece cap2325.3 off 0.2dm, using the offset command. Do you think it is ready for printing?
2525.4.3dm (28.9 KB)
cap 2325.3 off 0.2dm center.3dm (105 KB)
Hi Georod99
you could try some different steps
3. instead of project, use pull
5. instead of ExtrudeSrf, try OffsetSrf
Thanks. I used pull, but I obtain a triangle composed by three lines, not a surface. Therefore, I cannot use neither ExtrudeSrf nor OffsetSrf. Any suggestion?
You need to split the sphere with your pulled curves  and then use offsetsrf (solid=yes) on the small triangular surface… and either repeat for all the triangles or copy/array the first.
HTH, Jakob
Second question:
I used 1. sphere r=25, polyhedron, icosahedron, select a triangle, Pull.
 Idem r=25.2, and I obtained two triangles, but not two surfaces. Can I make them surfaces, then join them by the edges?
two concentric triangles.3dm (34.6 KB)
Could you be more specific? I have failed to split. Remember that I need only ONE triangle (curved). Once I have that, of a thickness of 2mm, solid, I can 3D print it.
Just to share with you: this is one of many designs that I have done. I can send you more if you want.
Another.
Yes, but I don’t know what I’m doing wrong.

Start with Polyhedron, > Icosahedron. Solid or Faces? (I have tried both).

Solid Tools, Sphere, Center, Radius > 25

Pull, Select curves and points to pull:
3a. I can select 3 sides of a triangle, 3b. Enter, Select surfaces and meshes that pull, Click sphere, and I have one piece.
And then I cannot continue.
3b. Pull, here sometimes I can Shift select the whole icosahedron, other times just one line.
If I Shift click Icosahedron without a command (before Pull), I can select the whole Icosa. But then when I write Pull, it asks to Select curves and points to pull. If I press Enter, nothing happens.
3c. I can select the whole Icosa selecting the 20 edges, one at a time. > Enter.
4c. Select Surf and Meshes that pull, > Sphere click and I have your third picture.
5c. Split. Select cutting objects (not sure what to do). I select one curved triangle and I don’t know how to continue.
I’m sorry, I have been working with Rhino for years, but I have only learned the commands that I needed (Polygon, Revolve, Rotate, etc. to make the models that I sent you. (The first models were made with PovRay, then I found Rhino). That’s it. Now I have been watching videos, using Help, but nothing.
One last request: Could you write the steps, like I have done from step 1.? Thanks.
well, if you start with the solid icosahedron, use the DupEdge command and select the entire solid with a rectangle including it and hit enter, now you should have the solid and all the edges as curves in the space, hide the solid and then, make the sphere.
At this point you should have the step 2 of my previous image.
Pulling the curves:
To pull the curves onto the sphere, first, hit the command Pull, then the command prompt ask you for the input curves, select the icosahedron curves, hit enter. Now the command ask you for the target surface, select the sphere and hit enter. Now you should have the Step 3.
Then select the sphere, run the split command and now select the cutting objects ( the pulled curves), hit enter. at this point you should have the entire sphere divided into 20 triangular shapes, delete 19 and there is the step 4.
Finally, run the OffsetSrf with the option Solid= yes , and that’s it.
Finalmente, gracias. Podemos comunicarnos en español, verdad?
Hi, Diego, how are you doing?
I have created a new design, but something is wrong with the mesh, may be the parameters I’m using. Please find attached the 3dm file. Could you review it so I can print it?
17 inv in del mesh.3dm (990 KB)