Hi Rudl,

> The file Test2 shows in a simple way, what I want.

Probably your best bet would be to form the object up as a solid (add some sides and a bottom to it), then do a shell on the solid, then possibly slice that up if needed.

When you form it as a solid you will be basically giving information on how the "side wall" areas are supposed to be formed, when you try to thicken an open surface the system does not know that you would like to have certain areas formed like this area here in your result here:



Offsetting of a plain surface will not generate something in that direction - that's a single fixed direction like an extrusion, an offset that thickens a surface will try to follow the surface normal and so wants to make a result that goes in this direction:



So thickening by offsetting a surface will not produce this kind of planar side wall that you have in your example:



But if you were to form this shape into a solid with a vertical planar wall on that area of the solid, then that's how the system will know what the desired "side wall" shape is supposed to be over there and should then have a better shot at building what you want.

Hopefully that may help explain the problem better - with the "thicken a surface" case the offsetting mechanism just does not know when it should try to deviate from a regular offset in order to make a common side wall boundary like you have built yourself there.

Thickening a solid should work better for you because the solid has all "side walls" defined for it and would not need to try and cook them up from nothing.

- Michael