For all you chemistry wizards, a question....

[Bill White]

I faintly remember a discussion from a hundred years ago (seem like it anyway) about a particular acid that can be used to "sharpen" files. I guess that the acid erodes the metal on the file body/teeth thus making the teeth sharper.
Was this phosphoric acid? Does it work, or does the process just eat away the hardened surface rendering the file teeth softer?
TIA.
Bill

[Dave Lehnert]

This may be of no help but I was on Micro-plane web site reading last night and they had a little article on they way they make the Micro-plane. Described a method like you had written in your post. May want to have a look and see if it helps at all.

[Alan Schwabacher]

I have not done it, but have read of the use of sulfuric acid to sharpen files. (Not phosphoric.) Apparently with this acid the points are eaten away more slowly than the smoother parts, so the files get sharper, but you need to monitor it so you don't go too far and destroy the file.

[harry strasil]

Items needed:
1. a large GLASS cake baking pan or dish.
2. full face shield, fume respirator, goggles, rubber gloves, rubber apron, full acid resistant sleeved jacket required. (lungs, eyes, skin, and hands are not off the shelf replacement items.)
3. 2 glass rods as long as dish is wide.
4. another container with pre mixed water and baking soda one small box of baking soda to a gallon of water.
5. a 3/8 or 1/2 inch dowel a bit longer than the dish is long.
6. some means to retrieve the file from the acid bath.
7. muratic acid, enough to cover the file completely and then some.
8. a container with soap and water and a small scrub brush.
9. another container with plain water.
10. a kitchen timer.
11. have someone handy and away from the operation to hose you down if you spill any acid on you and rush you to the ER if something does happen.
12. put the rods in the pan so the file lays on the rods off the bottom of the container.
13. center the pan cross ways on the dowel so the dowel is down the center of the length.
14. set the timer for 5 to 6 minutes.
15. carefully add the acid so that it covers the file completely plus some.
16. immediately start tipping the dish side to side slowly so as not to splash the acid, keep the acid moving over and under the file so that the acid will wash away the material eroded off.
17. when the timer goes off, quickly and carefully remove the file to the soda bath container and agitate it in this liquid for 2 minutes. any drops dripping off will destroy concrete, or any type of flooring.
18. scrub the file vigorously for 5 minutes in the plain water solution, then repeat steps 17 and 18.
19. dry the file completely and test it. repeat the whole process if necessary or Option 2: send to one of the commercial file sharpening services. Or Option 3: just buy a new file, its probably safer and cheaper. Option 2 or 3 are the safer, cheaper alternatives.
20. REMEMBER, YOU NOW HAVE A HAZARDOUS MATERIAL TO DISPOSE OF IN A SAFE MANNER. (THE HARD PART).

NO RESPONSABILITY OR LIABILITY IMPLIED OR GIVEN TO ANYONE ATTEMPTING THE PRECEDING HAZARDOUS PROCEDURE.

Its an old Blacksmith way of extending file life, some even used sulfuric (battery acid) in the old days.

[Bill Brehme]

Whew! I think I'll just throw em away.

[Bill White]

Anybody want to buy a somewhat dull 4 way woodworking file?
Thanks,
Bill

[Mark Mazzo]

Supposedly there is a liquid honing process that can be done (professionally). This is often done to rasps so, I assume it would also work for files.

There was a post on it in the Woodworking Magazine blog

I have never used this service, but thought that it might be what you are after.

[Zahid Naqvi]

I am surprised no one has mentioned citric acid yet, validated by none other than Sam Maloof himself. It is a food grade acid and can be purchased in powder form at any winery supplies store. Just let you files and rasps sit in it for a couple of hours. You will have to search the net for the exact concentration needed. But it is food safe, as in once you are done you can spill it in your flower beds and it will not cause any harm.
I have used it once to clean up some old rusted hand planes and other hardware, works great.

[harry strasil]

Zahid, citric acid, vinegar, phosporic acid (in soda pop) are all mild cleaning acids, and are not very powerful. they are used by knife makers to mildly etch pattern welded or damascus knives to bring out the pattern of the dissimilar metals for beauty.

[David Martino]

...think there was a recent thread but can't find it now, mentioned Boggs File in Southern California. They resharpen files and rasps using an industrial process similar to what you're talking about. Haven't used them myself. Google search Boggs and File and you'll find them.

[Juan Lauchu]

Bill,
I'm a HS Chemistry teacher and rather than "re-invent the wheel" here, check out this link. I think you will find what your are looking for in useful terms. Scroll down a bit to the "Removing Rust" section, I believe it is the 6th paragraph that begins a discussion on phosphoric acid. "Etching" is what I believe you are inquiring about.
http://www.metalwebnews.com/howto/rust/rust.html

[Dan Barr]

Harry,

just to raz you. youve got me stuck in an infinite loop of repeating steps 17 and 18. lolololol

v/r

dan