An alternative way to making a basic hollowed out ring in Tsplines instead of using straight Rhino and the cut trim and join commands. I think its quicker to model with more control over the finished form than using sweeps and profiles. Try to make sure a single surface is made (one that cannot be exploded) before you convert to Tsplines,otherwise you will need to weld the tspline joints that are produce from converting a polysurface, The video was in response to a question asked on forum