Hi telnoi, that is going to be a pretty tough one - you've got a solid there with 230 surfaces, and 562 edges in it.

Filleting all the edges would add like 500 or so little tiny surfaces extra to that, so that is going to be a pretty heavy and large model at the end.

The first thing that I would do to start with is to clean up the model to have as few surfaces as possible. For example, the inside surface of the ring is kind of broken up currently into several different surfaces, like this:



Getting rid of all of those little fragments and having just one big surface on the inside will tend to make filleting work better.

So to do that will require doing a kind of low level surgery on the object. To start with select all those inside faces, then use Edit/Separate to break them off from the main ring, then use Select/Invert and Edit/Hide to hide the rest of the ring. That will leave you with this:



Select just one edge from that object, like this:



Then do Select/Select All (or Ctrl+A) to select all edge curves like this:



Use Ctrl+C to copy those curves to the clipboard. Now select just one surface, then do Invert (it is handy to have this hooked up to a keyboard shortcut like I), then delete everything else, leaving just one piece:



Select all the edges of this piece (click on 1 and then use Ctrl+A):



Push Delete to untrim the surface and recover the full underlying surface:



Now push Ctrl+V to paste back in those curves we copied with Ctrl+C previously, that will look like this:



Go through and select the pieces you don't want to keep:



And then delete those. Now select the surface:



Then run Edit/Trim, and select those curves as the cutting objects:



Discard the top and bottom pieces, leaving you with this:



Select the surface, do Invert, then delete all the cutting curves.


Now you have a fully simplified center surface with no extra edges on it, you can now show the rest of the ring, join this new center piece with the other part, and now the edges along that center piece can be filleted successfully, to fillet just those edges you can select that center surface before running fillet, that will fillet all the edges that belong to that surface.

However, there are still some fillet problems that prevent the whole ring from being filleted still, I think that there will need to be some similar reconstruction to some other parts to get rid of some other unnecessary edges in the model first before it whole thing will be possible to be filleted.

Let me know once you have got the above part done and can fillet those edges connected to that inside surface (or if you have any problems finishing that stage), and then I can help you with the rest of the model some more.

- Michael