File for "fit" reasons not aesthetics. A string will normally set firmly into a V notch, but can slip around inside a saw kerf. I have a set of small jewelers flies - triangle, square, round, half round -- that attach to an included handle. I think the set was $10 at Ace hardware.
Gotcha, I'll have to look for jewelers files, sound useful. My razor saw seems to have worked ok, had to finesse it a bit for the wound string, but none appear to be moving around in their slot. Thanks for the tip.