Hi Daedalus,

> When I export this to render softwares I see sharp edges.
> Do you know How to smooth this ??

Typically you use the Fillet command to replace sharp edges with a rounded area.

But that places a small localized smooth surface in - for something like you are showing where it looks like you want to have a kind of continuous smooth broad area, it is usually better to do those kinds of things by building one larger surface for the smooth area, rather than building a number of small patches.

Also another big thing, is to not worry so much about building surfaces directly to the final 3D edge initially. I mean that to get a smooth larger surface you often will need to do that by creating a larger extended surface and then using Trim or Boolean commands to cut it to form the final edges. This is one of the major differences between NURBS modeling strategies and polygon modeling strategies.

So for example in this case that would mean building something like this for the base shape:



Notice how there I have temporarily ignored the cutout area and instead focused on one larger extended surface.

Then you draw a profile for the cut-out area:



Extrude it into a surface:



And now those surfaces can be trimmed with one another with the Edit/Trim command to produce the final shapes:




It is a lot easier to make a broad smooth surface by doing it actually as one surface instead of as a patchwork.

Anything that looks like it is a cutout, usually those are better to do in NURBS as actual cut-outs by Trims or Booleans, rather than kind of trying to construct surfaces "around the hole" instead which is what you would do for a polygon modeling system.

Hope this helps!

- Michael