Flipping explicit normals? Attaching objects with explicit normals!

[markus]

Hi

I have a model of an outboard engine imported as mesh from a STEP (cad file). I want to export the model to Unity, but some of the surfaces has inverted normals so I would like to flip those in 3dsmax before exporting as fbx. I would also like to attach all objects to a single mesh object, because having fewer objects is usually supposedly better for performance.

If I apply a normal modifier in 3dsmax the explicit normals are destroyed and the surfaces looks messy.

How can I flip the explicit normals in max and also flip the direction of faces?

Also if I try to attach objects that has explicit normals they are all destroyed.

On a sidenote: One workaround is to import the STEP file as bodyobjects and flip the surfaces before converting to mesh, however Body object does not handle all the surfaces as well as the mesh importer and is destroying parts of the models with more complex nurbs details. Mesh import is now apparently working much better than last year (max 2016), so Kudos for implementing that!

[lightcube · Accepted solution]

Instead of using Edit Mesh, try this:

1. Convert Imported Mesh to Editable Poly
2. Select Inverted Faces
3. Click Flip in modify tab options.

Use this method because Editable Poly won't destroy the explicit normal.

EDIT: A hint for selecting the bad faces more quickly, use the XView : Face Orientation. You can get to the XViews with the little Plus (+) Icon at top left of the viewport. If you turn on Select results, you should get the selection. Just orient view to good angle and select results. (Remember to deselect faces from other side of model.)

[markus]

Thanks for the Tip Shawn Olson! I wasn't aware that editable poly objects worked better for keeping surface normals. Is this behaviour a recent change in 3dsmax? Anyways, it's good to learn about max's little quirks and how to work around them.

I was also able to attach objects when converting to editable poly. One of the surfaces had some weird inverted shading normals, probably due to first using the edit mesh flipping, which has its own behaviour. I was able to fix it as you can see in this screencast. Btw, detaching in editable poly doesn't retain explicit normals, but I was able to work around it by duplicating the object and deleting the unwanted parts.

https://knowledge.autodesk.com/community/screencast/9be835ba-04a3-4320-a401-b91533089dc5

Let's hope one day AD will fix it so all modes including the various modifiers can work better with exlicit normals!