Nicholson makes a file cleaner. I've never used one, but it looks like it would work without damaging the file.

I've seen brushes for cleaning "chips" out of the "teeth" of files, but as for cleaning grease, etc, use what ever you use from detergent to gunk, the latter being the best I think for metal and strength.

I'd not spend a lot of time on old files, new ones are not very expensive, or maybe I haven't bought any good ones lately.

I use a "hand operated" wire brush, then wipe them down oil.

lmy

I spray my chainsaw files off with carb. cleaner, the blast and chemical seems to clean and blow the metal inbedded in the file pretty good.

Actually, what you are doing is cleaning the files, not sharpening them. Usually you can tell when a file is getting dull by light reflecting of the cutting edges. They look flattened on the edge, if you use a magnifying glass. My father used to refer to dull files as "whistlers," they make a whistling sound as they go over the metal (but don't cut worth anything!). There used to be a place that could resharpen files by immersing them in an acid bath, but I can't remember or find the name or location. I never sent them any files for reconditioning. The most important factor in getting the longest life from a file is to make certain you use pressure only on the forward (cutting) stroke, the second factor is to keep the file clean/out of rust producing environments. Buy good files, keep them clean!