Sharpening files - Anybody done it?

Gazz · Sep 4, 2011

So I have a fair quantity of files that have lost their edge and new ones are getting pricey, if you want quality. I know that there is a sharpening service out there and I believe it is basically an acid dip procedure. As I type this, I have a a half round file in a bucket of diluted muriatic acid to see if that will work. After a couple of hours, it would not cut any better and perhaps worse that it did before immersion. Would nitric or sulphuric be better? Does anybody have experience with doing this? Thanks for any replies!

gwilson · Sep 4, 2011

I have sharpened needle files by putting them in an acidic solution,and electro stripping them some. Don't get too carried away or risk losing too much tooth.

Steve in SoCal · Sep 4, 2011

Acid is not very good to use, it doesn't make the files sharp. There is a company in the L.A. area that uses a process called hydro-honing that makes files better than new. Boggs Tool & File Sharpening Company

This is the best way to restore files and if you ship a dozen or so not too costly.

Steve

gwilson · Sep 4, 2011

It isn't the acid that I use to sharpen files. It just has to conduct electricity so that the stripping can take place.

Zonko · Sep 4, 2011

Hi

I once read that a beaten up file will cut a biiit better if you let it rust .
The idea is most likely the same, reduce the burnishing that years of filing will haven given to the teeth and make the surface uneven so it abrades the workpiece better.

Hmm, its sad. We had a nice movie like 10 years ago when i was a boy.
It was a series on old and waning trades.

There was a job called a "Feilenhauer" , that would be a "file-beater"..or to be less litteral "file-carver, or graver" .

These guys annealed old files, used a special type of small planer to remove the teeth.
Then either a machine with a reciprocating chisel and automatic feed (for standard tipe files) or chisel,hammer and lots of experience were used to make new teeth. ( Hand work being used for special types of files)

Then harden after heating in a layer of a carburizing sludge made from flour,coal,water etc.

He was one of the last or the last of his trade.
Think he lived in ex eastern Germany , there communism had kept this trade alive for quite a while because old files were considered too valuable for scrap well into our age.

Well....i guess i have now met a capitalist who would appreciate the service of that old , dusty and venerable shop.

Clive603 · Sep 4, 2011

The instructions I've been meaning to try for mumble-mumble years call for Sulphuric Acid diluted to 1.25 specific gravity. Electrolyte grade sulphuric acid for use in automotive batteries is supplied at (I think) 1.265 specific gravity so it won't take much dilution to bring it down. My instructions suggest adding water to the acid which is contrary to standard chemical practice but the acid is already pretty dilute so, in practice, the process is probably safe enough. After all that's what happens when you top up a car battery and there are no untoward bubblings and splashes. (Doing it with concentrated acid is another story. Makes a spectacular demo if proper safety precautions can be a arranged but Don't Try This At Home definitely applies.) Dunno where you will find an inexpensive calibrated hydrometer tho'.

Should see bubbles in 5 to 10 minutes. If nothing much happens the acid is probably too strong. Sharpening takes 2 to 8 hours depending on file condition.

Clive

Greg Quenneville · Sep 4, 2011

I have used citric acid powder from the grocer's baking section. 15-20 minutes is a bucket all that's needed...much more and you destroy the teeth completely. A rinse in water + baking soda, then blast dry and oil to prevent rusting. I think you might get a couple of renewals this way before the file is toast.

Greg

gwilson · Sep 4, 2011

Make SURE that your file is scrupulously CLEAN and FREE of OIL before attempting to sharpen the teeth by any chemical method. Otherwise,you'll end up with a mess of uneven teeth,and places where the file was not sharpened at all.

morsetaper2 · Sep 4, 2011

I don't believe muriatic acid will effect steel. But I don't know for sure 100%. The reason I say this is we used to use muriatic acid on a q-tip to dissolve the smeared alum on a cylinder wall of a two stroke engine that had seized. The bores were steel, chrome, & nikasil where we used this technique.

technocrat · Sep 4, 2011

I have some very old depression era books which talk about file sharpening.

The idea was dip in acid, then wipe the top of the teeth clean with a rag. This makes the pits deeper and does not remove the cutting edge.

If you dip the whole lot in and leave it, you will take the teeth as well at the same or faster rate.

JoeE. · Sep 4, 2011

I wish I hadn't thrown it away a long time ago, but I had this big, hardbound book~ marbled edged paper, worm holes throughout, colored plates in a few places that was about everything you could ever imagine about machines and machine shop related items. Turn of the century or a little earlier.

Anyway, besides the line drawing of machines, the only thing I remember reading in that whole big book was an article about sharpening files. What I recall reading was they used something like a steam powered sandblaster and shot the abrasive at a low angle over the backs of the file teeth~ in other words- not against the cutting face.

That's all I remember about the process, and I thought it made sense. I have a box of dull files and a blasting cabinet. Maybe I should give it a try!

Gazz · Sep 5, 2011

Thanks for all the responses! I left the file in the diluted muriatic for a few more hours and it maybe cuts a bit better but certainly not good enough. I have been using muriatic for years to remove scale from stuff like hot rolled or from some of my forgings so I am sure that it will react with iron. I do have some ferric chloride and may try that too - I know that stuff will etch iron! I'll also look for some citric acid powder at the grocery store. Sounds like it may be useful stuff in any case. The wiping with the rag and sand blasting methods also sound interesting and I'll have to try those as well. I'll let you all know about any success or failures.

gwilson · Sep 5, 2011

I wouldn't sand blast fine cut files. Only the very coarse cut ones. I think my electro stripping method is the best option. You only need a few volts.

jCandlish · Sep 5, 2011

I've heard if you leave your files on the lawn overnight, garden gnomes come by and sharpen them.

lazlo · Sep 5, 2011

technocrat said:
The idea was dip in acid, then wipe the top of the teeth clean with a rag. This makes the pits deeper and does not remove the cutting edge.

If you dip the whole lot in and leave it, you will take the teeth as well at the same or faster rate.

Ah, thanks for that explanation! I never understood the geometry of file sharpening, since if you uniformly etch both sides of the V-shape, it would etch the tips off. But if you wipe the acid off the tips, you'll end up with a hollow-grind. Makes a lot more sense

I would imagine you'd want to wipe with something stiff, so it doesn't get down into the file grooves?

TDegenhart · Sep 5, 2011

I read these posts with interest. Many years ago when I worked for GE, there was a story going around about an engineer that had developed a means of sharpening files using acid. The theory as presented was that the would eat back the surfaces equally and gradually the rounded cutting edge would disappear. The fly in the ointment is that the acid does not attack the surfaces uniformly. Those that stick out, ala the cutting edge, are attacked quicker. The reason is field intensity which I won't go into (unless you want to). The acid will dull the file not sharpen it. This is the same reason that electro-polishing works. This is the same for rusting.

The same thing happens with sand blasting. The high points get knocked down. How many of you would sand blast finely honed cutting edge to make it cut better? None I hope. The file sharpening company mentioned earlier claims to use liquid honing. To me that is no different than a fine grade of sand blast.

Some success may be due to simply cleaning the file. Caustics such as drain cleaner remove oils and aluminum. I've noticed that cleaned this way, the file acts like its new.

But the proof is in the eating. Try your favorite method, look at the edge with a microscope before and after and make your own judgment.
Tom

Zonko · Sep 5, 2011

Hmmm

I see one flaw to your logic.

Dip some cold rolled into Hydrochloric.

It doesnt get polished !

I takes a matte finish.

I guess its got something to do with the reactivity of different grain in the steel.
But im not a Metallurgist , thats just a guess derived from the etching found on folded blades for decorative purposes, it attacks the different steels in a non uniform fashion.

Same for rusting.
While it will corrode details quicker than the bulk of an old object, it will leave pitting and uneven surface everywhere after removal (unless you remove in a way that burnishes the surface of the steel) .

Working in a Museum i have seen both. Files so blunt after decades of service, that you go nuts about it. The teeth are rounded and polished !
And rusty Stuff is everydays buisiness at the places.

I think a file that bad will benefit from anything that breaks up the surface just a tiny lil bit.
I guess the people of old were ok with that.

These "horror" files we have. They were certainly not worn down by us.
They are 1 1/2 feet long roughing files we use 5 times a year or so.
They were handed down from old shops etc. and i dont think their owners gave them to us for being worn. Much more likely their children did......

I guess its all a question of perspective.

John Welden · Sep 5, 2011

A really good way to sharpen files is to throw them away and buy new ones.

Files are disposable. I've probably got 50 files and they're all in good or decent shape because I refuse to keep a dull file.

How is acid or sandblasting going to sharpen anything? Do you sharpen knives, end mills or drill bits with acid? The file teeth are no different than any other cutting edge, they're just small. Rounding them over doesn't sharpen them.

Sorry for the rant. Dull files make me want to kill people.

Zonko · Sep 5, 2011

Kudos!

I hate these things aswell.

Big , ugly, blunt.

Its the same with hacksaws.

Put a brand new blade in one and its like ohhhhh, ahhhh, huuuuh, it relieves the pain.....

Recently another guy wanted to file something to shape with one of the old POS files. Told him to get an angle grinder. (Was some pretty strong sheet, like 1/8")

The truth is, we keep em because they are huge and look very old and fit perfectly in the museum setting.

Anyone doing production work ---> Clonk (Scrap bin sound [TM] )

Or pick up forging as a hobby and make something nice from the steel. :smoking:

oldvan · Sep 5, 2011

John Welden said:
Dull files make me want to kill people.

Please post your address so we may each put you on our Christmas list for a sharp file. Don't want to see your neighbor on the news, "He was always the quiet one." lol

Sharpening files - Anybody done it?

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