Why does offset surface fail!?

[andrew.richardsQGAWG]

Hi all, I really need some help with this, I am making a case for some electronics, I modelled the dimensions of the parts, combined them and then offset by 0.2mm. To create a larger version of the shape, this will be the internal dimension of the case, this worked fine. I have then made some changes to this body, and want to offset the surface again by 1.5mm, this will be the thickness of the case.

When I try to do the second offset, it always fails, I have had similar problems before which seem to be resolved when I individually select faces to offset as opposed to doing a marquee selection. This doesn't work, closing and reopening doesn't help either. I don't know what's wrong. Please help!

[JamieGilchrist]

can you share the design?

[chrisplyler]

I'm just guessing here....

It's probably because of that circular boss in the center, and the sides of the rectangular depression that it sits in, are closer together than your desired offset distance. The cylindrical face on the outside of that circular boss, and the sides of the rectangular depression, when offset outwards, obviously have to pass through each other. Fusion doesn't know how to handle that. In Fusion's mind, that creates a solid that warps through itself creating a negative space. Kind of like a Klein bottle. It doesn't know how to limit such an interference and modify the resulting geometry to eliminate it.

[andrew.richardsQGAWG]

Thanks for the reply both of you,

After a lot of messing around I just deleted the last few features on the timeline and then built them again. The offset works now. There was nothing wrong with the geometry it just seems to fail. I get this problem often and it is a real pain, especially seeing as after repetition the offset seems to work fine. There's something strange going on in the background, it doesn't seem to be a modelling mistake.