Rhino and normals.

I am preparing my Rhino model again and checking for any issues that might cause problems during Zcorp prototying and I found a really good checklist that includes this: Make sure that all surfaces are facing the same direction. This will eliminate NORMALS
in your models.

Does anyone know exactly what this means? I know about the “arrows” that show up when you click on “analyze direction” but what does that mean if it is a closed polysurface? Do the arrows have to point in the same direction: out?

And if not, does that cause problems when 3D printing? I think that might be what caused mine to fail during printing on the Zcorp; as mine printed only halfway. When going back to my part and exploding it, I found one surface in which it seems the arrows were pointing an opposing direction.

thanks guys.

A curve normal is defined as a line perpendicular to a tangent line to any point on a polynomial (curve). The length of that normal line is 1 over R (radius) or the reciprocal of the radius value at that point.

A surface normal is the same but with respect to a tangent line at any point on a surface. They point outwards. In some cases surface normals can get flipped as when rendering in 3d max or Alias. Hense you can’t see the render on that surface patch (backasswrds)

Ok, got it. So they always have to point outwards. Thanks!

If a Rhino object is sealed and watertight, you won’t have anything but aligned normals. If the object is “Bad” (see below) there can be parts with bad normals.

To check if an object is sealed use the command “what” it will show the polysurface is closed or open.

Use the command “ShowEdges” and see where the “naked edges” are. These are openings in your solid. Thin and nearly invisible gaps can be closed with the Analyze | Edge Tools | Join 2 Naked Edges command.

The last option to check is Analyze | Diagnostics | Select Bad Objects, this will reveal a defective structure. One approach to find the offending surface is to explode the solid, then Select Bad Objects again, and the bad surfaces(s) will be revealed, and you can try to fix them. and rejoin the set into a solid again.


Thanks for that useful info! I went back into my Rhino files and followed all those steps to check for errors in all my parts!