Hi wim, one of those 3 edge seems to be able to be filleted if you select it alone, this one here:



So first of all select that one by itself to get that part finished.

Then the other 2 I don't know why those don't fillet, I don't see any obvious reason for that, I suspect some kind of bug at work there.

But to get them filleted and work around the bug, you can select the 2 faces on either side of the problem edge, then use Edit > Separate on it to break those 2 faces (still joined to each other) apart from the main object. Now with it just having those 2 faces to deal with and no work to do on the side pieces you can select that same edge and it will fillet now.

After you have done that, select all those 3 pieces and use Edit > Join to glue them back together again, there are now some planar surfaces that need to be rebuilt to accomodate the hole that has been opened up in them from the fillet, it's this hole filling piece that the filleter failed to do properly.

The easiest way to rebuild the planes is to select the 2 recessed bottom planes on the bottom of the fillets to open up big holes there, and then select the whole piece and run Construct > Planar - all the planar holes will then be filled in and you'll have a solid. There will be some fragmented planes in the upper surface if you want to clean those up.

- Michael