Better is you post the 3Dm ;)

Else extrude it then Inset the face

Pleas .3dm)

With your
Scale it *3
Extrude it
Inset 0.5

don't understand you about scale

Select all your object
then Menu Scale : Click one point somewhere on the edge of your surface and Input 3 in the Box dialog
Your surface must be 3 times larger :)
Then extrude etc...

good, understand. but why we have to do this manipulation?

Michael will say to you! :)
Surrely something with the size!

Good got it. And the last question, whywe have to extrude it?

Maybe that works better with a volume for a curvated surface...
Wait and see the the Michael answer! :)

good thanx)!

Hi mir4ea, it looks like some kind of a bug in one of the shelling steps that Inset does. I haven't found out the specific bug yet but sometimes things with smooth boundaries can have the problem where one step generates a shape that is just very slightly not entirely smooth at its closure area and then if another step after that thinks that it's a sharp edge that needs to be extended and intersected and it is problematic to try to find the intersection on pieces that are nearly tangent to one another because they meet more at an area of overlap rather than at a distinct sharp intersection curve.

I'm not entirely sure that is the particular issue here though, it's unfortunately quite difficult to figure these things out.

So anyway for the time being you would need to use some alternate series of steps to get what you need here.

- Michael

Thanx Michael

Moved and rotated in Right cplane, and scaled by 30.
Extruded in -Z direction.
Inset only works in a narrow range around value of 1.

what do you mean "Moved and rotated in Right cplane" ?

Oops, should have said "moved and rotated the two most low and most wide points to the origin and X axis." (This is not really necessary, I just
like things to "line-up.")