I suppose this could be discussed in a Pub with mates 
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I bought a set of Needle Files (for use on Metal) at a garage sale on the weekend.There’s 12 in the set and they appear to be of good quality and have had little use..
There’s a bit of light rust on a few and also,some are clogged with gunk..
Anyone know the best way to clean and restore metal files to their former glory ?
A good stiff metal-wire brush, dragged parallel to the file grooves.
Thanks Trill,that works OK with a coarse file but Needle Files are very,very fine and a wire brush won’t get to the bottom of the grooves (?) ..
I’m wondering if there’s some sort of solvent or mild acid that will do the job.
weedie, vinegar, my man.
http://www.finewoodworking.com/item/113083/salt-and-vinegar-natures-rust-remover
Maybe a plastic scrubbing pad and soap or a surfactant to remove any embedded gunk first.
My woodturning tutor told me to immerse 2nd hand chisels I was given with rust spots in Diet coke overnight. Worked a treat. Something to do with the presence of phosphoric acid in the drink? He also said the cheaper the better ( more acidic?) so I used the stuff from Woolies for less than a dollar. Whether it would also degunk I don’t know but it might be worth a shot.
I have a product that’s for de-gunking sandpaper. It’s almost like eraser/rubber material. I use that when my needle files get gunked up from resinous woods.
Crepe latex, I should think.
If the gunk has petroleum in it (grease, oil or a preservative that has collected dirt) mineral spirits is a good almost-universal solvent. Soak overnight then brush out with a fine wire brush. These are easy to find in brass which will clean out the softened gunk without using up the edge on the file.
They restored pretty well.
I soaked them in degreaser overnight,rinsed thoroughly with a jet of water,sprayed on WD40 and then blasted that off with high pressure compressed air (this removed a lot more gunk) .
Thanks for your input amigos 
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http://www.amazon.com/Prostik-W1307-12-Inch-Abrasive-Cleaner/dp/B0000DD0L1
great stuff for sure.
RORY
I feel so “old-school” in face of the posts above.
What I do is to sharpen a flat-head jeweller’s screwdriver and clear the gunk manually using regular strokes along the “grain” of the file.
Takes a while, but is somewhat cathartic. And the screwdriver is tool-steel so it also sharpens the file a little.
Another way is to use a metal brush .. best it’s brass or some softer metal. It won’t work till the ends of the bristles get worn-in to the file profile - then it will go great. Scrub lightly with least distortion of the bristles for best effect.
Needle files are so cheap these days it hardly matters - what DOES matter is that you usually have to profile the edges of the file on a grinder or sander to ensure that there are less unintended cuts. That can take more time than the file is worth.
But there’s an upside - I keep a few blunt files for micro-cuts.
With whistles, sometimes you need to cut finer than your calliper can actually measure (to 3 decimal places).
And without very expensive laser-measuring equipment, the measure of a calliper cannot be well trusted due to micro-distortions of minute angles imparted from the noise in your muscles and eyes.
At that point, I abandon the calliper and start using my ear - those are the times a blunt needle-file becomes a very handy thing indeed!
I also have to mention that the knife should be used as much as possible. As a “knife-philistine” myself .. well .. I have seen true masters use nothing but the blade. I still resort to files .. but only after I pass my “trust-threshold” of my blade.
It gets better, but I suspect a few more years .. thank the god(s) for files!
(I have seen master bladesmen spend a good deal more time getting an edge than I ever had to spend clearing a file.)
At the end of the day .. the craft of whistles has to do with the music. We can obsess about cosmetic or exactitude values, but if the thing performs well as a musical instrument .. the cosmetics and excellence of craft become “nice to haves” .. lesser in the hierarchy of craft - and superfluous in the objective of the musician - our patron and master.
Although ..there are subtle influences that the cosmetic craft may have on the player. Still .. subordinate. We serve the skill of the player . the “art”.
I am in awe at the dedication required to deliver such a thing! To me, this is the essence of “value”. So many people, doing so much to make life worth living for all!
Hope this helps!
I don’t find that unusual myself. I use a #11 Xacto knife blade to clear the crap. It is a meditative process. Steel brushes, file cards, brass brushes, WD40, etc. all work to a degree for build-up in some instances. The brass brush is the workhorse for me, always on the bench with the files. I hate working with aluminum at times - dirty, sticky stuff. Some materials just require the knife blade.
Feadoggie