Nice I didn't know there is a command to flip faces normal.
But why when a face is joined to another they don't have the same normal orientation?

Sure Michael will answer for this particular case! :)

HI Mala,

re:
> Why can't this structure be extruded?

Extrude works on either curves or single surfaces (or also on faces selected on a solid which will automatically boolean with the solid).

Your object is neither of those, it is a "joined surface" made up of 2 surfaces joined together.

To extrude it, select it and run Edit > Separate. Then select the 2 surfaces and run Construct > Extrude.

Since the surfaces are not planar it will default to extruding in the z axis direction which would make a degenerate object so you will need to use the "Set dir" option and pick 2 points to define a valid extrusion direction.

Also note that if you want a result that has uniform thickness you should use Construct > Offset > Shell instead of Extrude. You don't need to separate it first if using Shell.

- Michael

@pafurijaz

> But why when a face is joined to another they don't have the same normal orientation?

They do, and there isn't any wrong direction on this object.

@Pilou, why do you think there is a wrong direction here?

- Michael

The fact that extrude works for both in the same time only when on face is flipped...

Hi Pilou,

re:
> The fact that extrude works for both in the same time only when on face is flipped...

It doesn't do that.

Flip can flip the direction of selected curves or a surface or entire joined surface.

It doesn't do anything on a face selection.

Extrude does work on this if one or both faces are selected, without any flipping.

However extruding a face selection also tries to do a boolean with the extrusion and that won't work very well if the object isn't a solid. You can turn off the boolean by setting the "Keep separate" option.

So select one or both faces, use "Set dir" and set "Keep separate", should work - no flipping needed.

- Michael

Thanks for the precisions!

But curious!

Hi Pilou, that's all normal behavior.

re:
> Just Flip one face

Does nothing


> Select All

https://moi3d.com/4.0/docs/moi_command_reference6.htm#selectall

THx for the precision : so a selective selection! :)