Hi Giammarco,

I looked at your drawing and realized that @dgorsman was right - it is practically impossible to convert 3d faces that form the model into 3d Solids or Meshes in AutoCAD.

I used Rhinoceros for Mac to convert 3d faces in your drawing to 3D Solids, but at first I reduced meshes by 90% in Rhinoceros.

You can look at the result in attached drawings - Rhino export-solids.dwg - as it was exported from Rhino (solids)

and Rhino export-meshes.dwg - I converted solids, created in Rhino to Meshes to reduce file size.

Maxim