A: The same ultrasonic cleaner and steam cleaner you might use on jewelry will also clean up your files. The heat of the steam cleaning leaves the file warm enough so residual moisture evaporates quickly, but to be safe against rust, I sometimes give the file a quick spray of WD-40, and then wipe off what I can.

But I don’t always remember to do this, and frankly, my files don’t seem to get any more rusty from this treatment than the coarser ones I use a card on. You may also find the small rotary wire brushes you put in your flex shaft to be useful, though not so much on the finest file teeth sizes. Brass brushes take out coarse bits stuck in the teeth but leave a bit of brassy color on the steel. Nickel silver or steel wire works a bit better. The action of the flex shaft driving the brush gives it a lot more effective action than a manually driven brush, and it’s quicker too. But again, for the cleanest file, I just use the ultrasonic and steam cleaners.