Hard to believe, I know. Actually, I found an old thread mentioning that Derek had posted a video on the topic, but I don't know where to find it.
Not too long ago, I bought a couple of L-N joinery floats, and I've found all sorts of uses for the face float. I've sharpened it a couple-three times using either a 6" XX-slim file. (I tried a 5" XX-slim, and it works okay, but the teeth of the float are deeper than 1/2 of the width of the side of the file. If you want to use the file going both directions without overlapping the areas on the file, you need the 6".) This last time, I can't seem to get the float as sharp as I have before. So. . . what techniques do you use for sharpening floats?