How can I flip the normal on a surface?

Tom_Schoenhofer

Creating a surface using LOFT there is no option for which side is the outside. I think it assumes the top surface is always convex? This has never been a problem before but now when exporting a surface for VR or sending to someone else the image or surface object appears backside out. 

Thanks

Tom_Schoenhofer

OK I found the answer. I was half way there.
Loft the surface, it has the normal backwards.
Then offset the surface a very small amount, I used .1mm .
Then use DeleteFace on the outside (original surface) and check leave open.
This leaves the flipped normal surface on the inside.
All good now for export. 

John_P_Desilets

 Please post a link to your document and share it as public. This way we can take a look at the geometry. Thanks! 

Tom_Schoenhofer

Geometry is crude. Its from a scan of the inside, with closed splines fit through the scan and the surface lofted over these curves. There is no outside, everything is inside, but the loft surface is normal outside.   https://cad.onshape.com/documents/6292431027cfd004f2f0c912/w/38e499b71c239ac04389e4fb/e/4f17d9ce985c9b1e450fba24
If there is no way to flip the normal it's no big deal, I just thought Id ask because I couldn't find a solution.

John_P_Desilets

I don't know if I fully understand the issue. Would it be possible to illustrate what you mean? Is there a specific loft that you are referring to? 

Tom_Schoenhofer

There are 5 lofts, they are created on these closed curves. I choose the curves in order and loft and the normal is to the outside. That's fine in OnShape but after export when you look at what is supposed to the surface created you are looking at the inside of the surface because the surface normal is the wrong way.  
I figured a workaround- I select the surface and create a part with thicken that is 1mm thick. So I now have two close surfaces = normals pointing both ways and at least the correct surface is visible now.  

John_P_Desilets

If you create a closed sketch profile you can just loft a solid instead. Or, you can enclose the surface to form a solid afterwards. I am still not 100% on what you mean by normal to the outside. Surfaces are single sided with no mass or thickness. If you found a work around that is great news! 

Tom_Schoenhofer

In this case it's like a tunnel. If you loft profiles, and use solid, you create a solid of the air in the tunnel, surface direction to the outside, which is not right. The normal of the surface of a tunnel is to the inside. I don't have a surface of the outside of the hull in this case and I don't need one because all the objects are on the inside. 
I also tried offset surface where you can copy and/or offset a surface in either direction but this does not change its surface normal.

Tom_Schoenhofer

OK I found the answer. I was half way there.
Loft the surface, it has the normal backwards.
Then offset the surface a very small amount, I used .1mm .
Then use DeleteFace on the outside (original surface) and check leave open.
This leaves the flipped normal surface on the inside.
All good now for export.