Hi Chris, the part about that fillet that is difficult for MoI's filleting engine to handle is that it would kind of open up some holes in the model.

So take this edge for example, this is one of the ones that you had highlighted:



When a fillet is constructed along that edge, it's going to have some gaps open up in the bottom and top of it here:



So I'm not exactly sure what kind of shape you want to get out of that, do you want something with those holes filled in with planar pieces? That may be kind of weird on the top part though making a kind of shelf sticking out.

Also could you tell me what fillet radius you're trying to use? That can be difficult to put a larger fillet radius on top of an already filleted smaller radius like you've got along the top edge there already. You'll usually want to apply fillets starting with the larger sized one first instead of doing the smaller ones first in areas where they are going to be running into one another.

The way I produced the fillet that I show above was to extract out these 2 faces from the main object:



And then that edge between them will fillet because it doesn't have all those side pieces on the top and bottom that it doesn't know how to deal with. The faces are extracted into their own object by selecting them and using the Edit > Separate command. You may need to do some of that kind of work to get this how you want it. Then you use Edit > Join later on to glue the pieces back into a solid again.


But if you could tell me what radius you want, that would help give me a better idea of what kind of shape you are looking for.

Also depending on how you want things to look like on the top edge, you may need to select not just that one larger edge but also this one here:



So that the filleter will also try to round off that piece as well, making a rounded juncture there instead of it trying to open up a hole there:



This example above was with the whole upper part separated off with Edit > Separate.

- Michael