"Failed to Boolean bodies together" and not sure where to go from here

[kyoukaisenki85]

I've been working with a model that I imported from an stl (went through the whole conversion from mesh stuff). I realized I needed an internal part to be 4mm higher, and the easiest way I thought of was to copy the model, cut out the outside, and simply move the innards up 4mm and combine the 2 models at the end.
Long story short, I'm trying to combine an imported model with its own part, and I'm getting the message "Failed to Boolean bodies together" I tried google, but it was unclear what my next step should be. I'm happy to clarify further. Thanks!

[hamid.sh.]

Could you share the file or at least a screenshot with Timeline and Bodies folder of the Browser expanded? Have you done a faceted conversion or prismatic? But anyway, most of the times mesh to BRep conversion won't give you a good geometry to work with. 

[jeff_strater]

faceted mesh to BRep models are often the source of Combine failures.  Combine will fail when the geometries are nearly the same geometry, and likely this is the case in your model.  Sometimes you can get away with moving a body by .5mm or so to get clean overlap, and that will help the Combine to succeed.  You might be better off just rebuilding the model, if it is simple enough, using native Fusion geometry.  If you share your model, we can take a look at it directly.