How to sharpen a file.

There was one step that did not seem to be presented:

Any sharpening would occur due to the acid dissolving an even layer 

of iron on the file.  So the acid must have access to the surface of the metal.

Any wax, grease, or oil on the surface could occlude the water from the metal.

A pre-cleaning with detergent, water rinse and mineral spirit tx would give a fresh

iron surface.


The mineral acids discussed can be potentially dangerous and a problem to discard.

I am wondering ( as a denken experiment ) if electrolysis would not be a safer method?

The file could be wired as the donor and a copper rod to accept.  I can't recall ever 

seeing iron being used to plate another metal, but it should behave as any other metal.

The slightly salty water medium should be no problem to discard.  I have not looked it up,

but I think that since Fe has a positive charge, the copper rod should get the negative charge.

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Good point Jaeger about thoroughly cleaning the file.  

Another source of H2SO4 (sulfiuric acid) is the automobile parts store, where I got a supply of battery acid.   

Whatever one does, be careful with this chemical.                               Duff  

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I introduced myself to one property of sulfuric acid inadvertently.  It is intensely hygroscopic.

That is - it readily combines with water.  It takes a lot of energy to remove the water, so

when it does combine with water it gives back that energy as heat.  On your skin, it feels like

a jet of live steam has hit it.  Adding water to acid, the water instantly turns to steam and blows

out of the liquid - taking some of the liquid with it.   I have never added water to acid, but I 

did discover that reagent sulfuric acid is thick and does not pour like water.  It tends to come back

down the surface of the container it is poured from.  Pouring it from a beaker with your thumb on

the bottom of the beaker is really not a good way to do it.

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In German we have a saying: "Erst das Wasser, dann die Säure - sonst geschieht das Ungeheure" - in free translation "First the water, then the acid - otherwise you are in deep ****". The first drops of water vapourise immediately and the steam carries with drops of acid ... I am sort of chemist, a geochemist to be precise, and I know what I am talking about. Guess why - well not because I made the mistake, but I have seen others doing it and nearly hitting me with a spout of hot sulfuric acid ... :o


I think the electrolytic method would be much safer and more controllable. The other electrode needs to be more inert than the iron (conversely, one uses less inert metals, such as zinc, to protect iron/steel ship parts). I would doubt, however, it is worth the effort. As was noted above, the surface would rather be eaten away quite uniformely, while in sharpening you would need to eat away the bent-over and flattened teeth. Before the process you would also need to clean the file from any dirt, grease, stuck-on filings, etc. in order to present a metallic clean surface.


It is better to maintain the files carefully and to buy a new one every 20 odd years or so ...

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Think buying new every now and then is the way to go, although I had a friend, now gone, give his files the acid treatment, he liked the result. Buying new and throwing the old in a box has been the norm around here for a very long time and there must be over 60 pounds of old files, rasps and hoof files collected. Think I will keep them, they don't take up much room and never know when I will need to make a good knife.


Edited by jud
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Buying new files is much safer, and taking good care of them is excellent advice.  

Files should be stored in such a way that they do not bang into each other.  

I store mine in a wood drawer with thin wood dividers, and some have card board sleeves slipped over the teeth.

My micro files are also stored with corrugated card board separaters and the really small ones are pushed into the the end of the card board.


Old files can be made into excellent knives and turning chisels.  Be careful not to draw the temper while grinding.       Duff

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