Hi albehany - the boolean commands like Merge and Union are primarily for combining 2 or more solid objects with each other, with the objects being intersected and some material removed. The merge command cuts the objects with each other and leaves all the pieces, while boolean union keeps the outside pieces and removes the pieces that were contained within both volumes.

Neither Merge nor Union would work on your object here, for a couple of reasons - the first is that you don't have multiple solids, you've got just one object. The second is that your object is not a closed solid, it has several open edges.

It tends to be better to build something like this by starting with a solid and then doing booleans on it, it kind of looks like you may be building things out of individual surfaces rather than working with solids?

Are you coming from a polygon modeling background? You might check out here for some tips for polygon modelers:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2


Fillet is having problems due to a degenerate slivery-thin face that's right along the area you want to fillet, in these areas here:




If you look closely at the indicated areas above, you can see the edges in those spots are slightly darker - that means that there isn't just one edge there which is what you'd need in order to do a fillet. When it's a bit darker like that, that means there are multiple edges being drawn on top of each other there. Then I deleted some of the surrounding faces and then could more easily see these slivery thin surface fragments:




Filleting will definitely get confused by that type of structure with some extremely slivery thin faces.

The other thing that would help is if the model had larger surfaces like the front face being all one surface rather than it being multiple pieces like you currently have.

- Michael