Hi Pilou - scaling is certainly an easy way to get a result, but it will give you a different shape than shelling.

Shelling uses an offset calculation, which creates a shape that has the same thickness everywhere.

The scaling result will create a shape that has a varying thickness to it, except in a few special cases like for a circle or a sphere.

Here is a bit of an exaggerated example to illustrate.

Say you have this shape:



If you use an Offset on it, it will create a shape with a constant thickness:



Notice how the proportions of the shape have changed in the offset? It is not just a scaled copy of the original.

Scaling only would do something like this:




For shapes that are absolutely symmetrical about a center point like a sphere or circle, then that is a special case where scaling and offsetting are equivalent, but for the general case they are not the same thing.

- Michael