To create independent surfaces out of top-level NURBS curve objects, use the Extrude and Lathe modifiers. Extrude adds height to the curve, creating a shape by sweeping it along the curve’s local Z-axis. Lathe creates a surface of rotation, revolving the shape along a specified axis.
The Extrude and Lathe modifiers treat NURBS curves the same way they treat shapes. The advantage of using NURBS curves instead of shapes is in the different possible shapes that NURBS geometry and editing provide.
Tip: When you create a complicated surface, especially with the Lathe modifier, you often want to render both sides of the surface. Turn on Force 2-Sided in the Render Scene dialog to see both sides of the extruded or lathed surface. To see both sides in viewports, turn on Force 2-Sided in the Viewport Configuration dialog.
By default, an object with Extrude or Lathe collapses to an Editable Mesh object. To have Extrude or Lathe output collapse to a NURBS object, change the setting to NURBS in the Output area of the Extrude or Lathe rollout, and then collapse the modifier stack.
The Edit Stack button also lets you turn a NURBS curve into a NURBS surface object. This doesn’t immediately make the curve a surfaceinstead, the curve becomes a curve sub-object of the surface object, and you can then use NURBS editing to create other sub-objects, including surface sub-objects.