So many tools we jewelers use need to be modified for our personal
tastes and needs. One example is the “safe edge” on files. A safe
edge is that smooth edge on a flat file which allows the accurate
filing of steps without undercutting, or a situation where you want
to file smooth an area of metal while not affecting an adjoining
Shaping a prong on a set stone (without scratching the stone) is
another use for a file with a truly safe edge.
I seldom find an “off the rack” file that has a safe edge smooth
enough for my needs.
To modify my files’ safe edges, I use a belt sander, first removing
the side cover to expose the upper wheel of the belt sander. Using a
coarse belt, I hold my flat file by the handle, safe edge facing the
belt, my left thumb and forefinger pinching the file’s tip. With this
two-handed position, and the belt sander running, I make a careful
"run" across the top of the sanding belt, starting at the file’s tip,
and pushing the file’s edge along the center of the belt until the
entire length of the safe edge has been ground. I do this quickly and
precisely, always keeping the file’s edge perpendicular to the belt,
and removing the file from the belt at the end of the stroke, to let
it cool. This process actually creates very little heat, which could
harm the file’s temper.
When the teeth on the file’s edge have been removed, or the
smoothness I’m looking for is achieved, I then switch to a finer belt
and repeat this process until the edge is quite smooth. This will
leave a very smooth edge, and if done carefully, will not affect the
file’s cutting performance on it’s flat cutting surfaces.