Well yeah you're destroying your custom normals when you edit the geometry. This is an issue i had with CAD models needing some fixes aswell. The easiest way to fix this would be to use, after your edits, any face weight normal script like this : http://www.bytehazard.com/articles/wnormals.html(You need to have 1 smoothing…
I guess this face weight normal script you mentioned is pretty much the same as this http://www.scriptspot.com/3ds-max/scripts/improved-face-weighted-normals ? Because that's the one I'm using. It fixes some areas but not all of it (like shown in the screenshot): And two other methods sounds complicated and with their own…