Pilou:last one is perfect..Bravo' !

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Peter<<Is there any specific reason why you made it so big? (grid is very small on your file) Or that's just coincidence i presume?>>
I did a quick sketch without using your model.I see you are new here so i just show you other alternatives:In future you'll discover many ways to get the same shape

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Michael<<Hopefully more cases like this will work in the future as the people who make the geometry library that MoI uses continue to tune it up. This particular "disappearing fillet" case comes up fairly often so I will ask them about it specifically.>>

disappearing fillet is an old problem,i found also bool-diff disappearing and so when model start to be more complex and the build of it is not always correct
while you are improving Moi with new good tools the other people don't run like you..i mean:sometime it's like a Ferrari with just one gallon of fuel in the tank
when the geometry library fails i have a try exporting in 123D to do the same operation,if fails there too i understand i followed a wrong workflow but most of the times it works
so maybe ( i say maybe) could be better to have a stronger library,that is "the core" of a modeling app,than have new tools...but unfortunately it not depends by you