Sharpening or restoring dulled nut files?

[Mike Kolb]

I've built a sizable collection of nut files over the years...  sometimes shuddering to think what the total investment has been, and that's what leads me to my question.

An increasing number of the oft-used ones have, over time, dulled.  I've already gone the route of breaking-off the ends to present a fresher surface area, but that can only be done so often.

Curious if anyone has experience with acid-sharpening nut files?  If so, what sort of acid and at what strength?  I'd also imagine there must be an optimum length of time for sharpening without causing irreversible damage.

Or maybe I'm hoping for a magic fix that ain't there?!  Curious about all comments... thanks. 

[Steve Bettesworth]

Never heard of this before. I'd always treated files as disposable. However, I looked into some of the claims and looked at the film on YouTube. I still think it's all 'snake oil',  how can dipping a tool in acid sharpen it?

The only explanation I can come up with is that the acid corrodes areas of the file making it more like a strip of sandpaper rather than the precision tool that it is. This would also explain Frank's claim of sharpening a file by leaving it in the rain. Areas of oxidation would give a more abrasive edge, and therefore appear sharper. I have to add though that most of my life as a fitter I worked on RN ships and tools were often wet but I never noticed any improvement in the cutting of a file. 

If anyone can actually explain scientifically  how dunking a file in acid actually sharpens it I would love to know.

[Ed Minch]

I can attest that it works because I have been doing it for about 15 years.  At first I used muriatic acid but found that I was not attentive enough so switched to citric acid.  I have also sent 2 batches to Boggs.  The smaller the file, the harder it is to keep track of, and the smallest I have done is a very small triangular saw sharpening file.  A nut file would be difficult to catch at the right time, but since they are used in softer material, they probably don't need to be perfect to be effective.

Here is what I have always pictured happens - although I don't know this to be true.  When a sharp edge gets dull, it has rounded over to some extent.  When you sharpen on a stone, you remove material from one or both flats to get to a point where the edge is pointy again.  The acid does the same thing - it removes material from both flats.

Here is something recently added to the Boggs website:

"SHARPENING SERVICES may feature the advantages of our ABRASIVE BLAST LIQUID HONING PROCESS to sharpen files and other small tooth tools as seen in American Machinist, Anvil's Ring and many other industry publications.  Using steam, we relief-grind with abrasive blasting, taking material from the back edge of the tool to reform and sharpen the edge.  Our process will give you the sharpest edge possible."

Ed

[Andrew]

I wonder how well strong vinegar would work. Id like to give it a try on the old beater files I use on my mower blades and hatchets etc.

Steve B, I imagine the acid treatment being discussed is similar to that of chemically etched 'razor' files. I dont think it's snake oil.

[Steve Bettesworth]

Still very sceptical about file sharpening. Looked on line and been mulling it over. Having an engineering and science background it just seemed bunkum to me.  I felt that there was possible merit in the process if the acid evenly etched the file's steel. But this is dubious as the etching effect will be down to the surface area exposed to the acid, so the teeth radius would be reduced;  while the distances between them would be greater.  This may give you a sharper file it won’t last as long before you have to repeat the miracle.

 

What I now think happens is that the acid attacks the material trapped between the file teeth and may remove the burrs on the teeth, (this would agree with the idea that surface area is a factor),  this combined with very thorough physical cleaning will give an improved performance/life to a file.

 

Not saying that this is what actually happens I'm just trying to fully get my head around all this and understand precisely what is happening.

I've spent too long on the net looking at this and looking it up in my old engineering books, I’ve seen all sorts of claims made all of which I'm prepared to believe, but I don’t understand why Americans can’t say aluminium! 

[Andrew]

Because thats not how it's spelled lol :P (Im Canadian btw)

[Steve Bettesworth]

Aluminium, not Aloominum!

[Russell Vance]

Thankyou Steve,

While English hasn't been spoken in the U.S. for some time now it's nice to see that there is still a vestige of civilization and literacy left in the far flung echelons of the Western world - and;  a Canadian siding with the tin-tanks - wonders never cease, eh bro!  

Rusty of the antipodes.

[Steve Bettesworth]

Thanks Rusty. Good to see rhyming slang is alive and well. Over here now the colonialists  are more likely to be referred to as septics.

Steve of the Mother Country.

[Ed Minch]

Steve

Rather than over think this, why not grab one of your beat up files and give it a try?  You could prove it to yourself one way or the other in a day or two.

Ed

[Steve Bettesworth]

Possibly Ed, but you know how things eat at your brain and you try to rationalise things. Like why is  Sepp Blatter still president of FIFA or why Cabbage Patch Kidz were popular!

[Ed Minch]

Steve

I hear you.

Sodium, Magnesium, Aluminium.

Ed

[Andrew]

Apparently it is spelled either with or without the second i... Still sounds silly to me.