Hi Sun, I've attached a new "fully cleaned" 3DM file version that seems to be able to fillet everything ok at radius = 0.05, giving this:



I've attached the base unfilleted version so you will be able to apply other fillet values if you want.

Here's a tip on building the selection for the fillet more easily - start by zooming in a bit and selecting just one of the side-wall faces of the model like this one:



With that one face selected it will make window selection target faces also, and with just a couple of strategic window selects you can get all the other side wall faces.

Do one window select like this:



And another window select like this:



And then that will end up with all the side wall pieces selected like this:



You can now run fillet directly after that last selection - when you give fillet a face selection all the edges belonging to those faces will be targeted for selection.

In some cases like this it can be more convenient to select faces for the input to fillet rather than edges, since there are kind of fewer face pieces than edges to wrangle with.

Note that on the window selection steps you want to start the window on the let and drag it towards the right. By dragging in the left-to-right direction, only things completely contained inside the window will be targeted for selection. If you start on the right-hand side and drag towards the left you will get what is called a "crossing" window (the outline box will show as dashed instead of solid in crossing mode) which grabs anything that intersects the window even just partially. That crossing mode can be useful in other situations but for this one you want to do 2 non-crossing window selections because that then avoids the wider faces at the top and bottom from being selected.


When you then do the fillet it will crunch away for possibly a few minutes but then seems to get everything done ok this time.


Hope this helps!

- Michael