The Rhino 3D program is easy to work with.
Rhino works from shapes and lines that form geometric surfaces and solids.
To draw my ring I started by drawing two circles with the diameter with the measurement of a finger.
Then I used the rotate tool so the two circles do not get symmetrical, and the visible top part of the ring gets bigger.
After that I used the loft tool to join the two circles to a surface.
To make the surface a solid with 1mm thick, I used the "Offset Surface" tool and gave it the indications to make the thickness 1mm out.
After having the base of my ring drawn in 3D, I started giving personality to the ring.
My goal is for the ring to have several circles together cut out to look like the filigree technique that I explained earlier.
I drew several strange shapes over the ring with the "control points curve" tool. And moved and resized the forms of siege until they had the appearance that I desired.
Then with the "project" tool I designed the lines drawn on the surface of the ring, as we can see in the images below.
The lines stayed on the shape of the ring and with the tool "trim" and "split" I started to cut out the circular zones I did not want in the ring.
After that some of the more irregular circles that I cut in the ring lost their thickness, and so I used the "Blend surface" tool to join them.
Finally I clicked on "join" and my ring closed all the surfaces getting in a so polysurface ready to print on the printer.