I forget how I came across the idea of using the coffee filter. I remember that I used to use them for cleaning brushes & the paint cup of my airbrush. It probably happened when I tilted the airbrush a little too much over a plane I was painting......
I have a tendency to be frugal & resourceful (read : cheap). I sand with 400, 600, & 1500 grit, then get out the filter. Works like a charm every time. I fold it into a pad, and when it gets soft, I re-fold it & use another "side." They last fairly long that way.
Glad to hear that you had success with it !