not a fillet problem, but BOOLEAN! =)

 From:  Michael Gibson
4137.5 In reply to 4137.1 
Hi Chris, I'm not entirely sure what went wrong there, but it looks like these 2 pieces here (shown selected) appear to be just very slightly on different planes:

I extracted the edges around those surfaces and zoomed in and it appears to be just a tiny bit off only on this side here (where the W was at):

When I zoom in really close in the side view that selected edge looks like this:

So it looks like there's a tiny angle between those 2 planar pieces with a bit more deviation on the side where the W was at. If you just select only the R and the main shape and not the W, that seems to boolean union ok without any other tweaking. But the very slight dip on the side of the W seems to be messing up getting that piece unioned. It's a very tiny sized dip, something like 0.0002 units but enough to make it difficult to resolve in that area.

The booleans have to do a lot more work to resolve things that have coincident or nearly coincident surfaces that are overlapping each other, so if you make pieces push through each other instead of being exactly (or nearly as in this case) coincident that will tend to solve issues like this.

Also the filleter does not tend to really like to deal with planes that are split up into multiple fragments like this even if they are completely aligned with each other. So it tends to be better to have just one big plane for areas like this instead of having multiple plane fragment pieces stuck together.

A quick way to tune up areas that have multiple side-by-side planes into just one plane surface is to delete the existing pieces leaving a hole, and then select the object and run Construct > Planar which will fill in planar holes (if they're planar within a 0.001 tolerance which it is in this case even including the little dip) with just one big trimmed plane.

Doing that for your case here (getting just 1 plane in that spot instead of 2 pieces) will also allow the boolean union to work as well, without modifying the letters.

But one of the easiest things you can do if you run into a boolean problem is to get the pieces pushing through each other by a little bit instead of skimming each other.

- Michael