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. 

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Having been a fitter and turner for 12 years up until 1988 when I had a change of career; I served a 4 year apprenticeship one year of which I spent with a file in my hand and it was often the go to tool of the trade. So I do know a little about them. It depends on what material the file has been used on. A file that has been used to file brass is often useless on steel. If used to make bone nuts then the soft material should not over dull the file. However they will get clogged and this can reduce their effectiveness. The best thing to do is to keep them clean, use a file card or a wire brush, rub blackboard chalk into the file this will prevent clogging and occasionally bang the file to clear it while in use. I would not worry about sharpening a file, in fact it's something I've never even considered. Once a file is blunt or worn its pretty useless, throw them out and buy new. The only thing we ever did with an old file was to heat treat it to make scrapers. 

One of my favorite little chisels is made from an old .056" nut file.

I use it for cleaning glue off the end of fingerboards, cleaning the corners of nut pockets, trimming binding, etc. Anything with just a thumb and a couple of fingers. No handle weight to fight.

I expect YouTube is loaded with video examples of acid etching files.  

I recall reading about a hundred years ago in Popular Mechanix or someplace about "rust sharpening" files by tossing 'em out on the front lawn overnight. . .

Hmmm, "rust sharpening"... I like it.  Sounds like a Mother Jones version of acid-etching, in that they'll accomplish the same thing by using a chemical reaction to sharpen. Now that you mention it, I found a pair of old (really, really old) rusted-shut scissors in the yard a few years back, and the points were like needles.

Without trying to belabor the point too badly, I have a love/hate relationship with YouTube.  Living in the sticks means our only available internet connection is via satellite.  No broadband fiber optics, no cable, oh... and we're in a cellphone "dead zone", so no 4G connection either.  

Those of you with satellite internet know the drill... there's a monthly upload/download limit.... ours is 10GB/month. A little quick math and you can see that just a few YouTubes will chew that allotment up in no time flat, hence the "hate" part of the relationship. The "love" part is going to someone's home with a full-time connection and going nuts watching YouTubes:)

Having said that, if anyone wants to do my homework and check a few YouTubes on acid-sharpening, I'd be grateful.

Point well-taken, Steve. I've cleaned and file-carded the few dulled files to death.... with no improvement, so I'm guessing they're really worn. Still curious, though, that bone would have such an effect, but the proof seems to be in the dull pudding.  It's only a few files (maybe 3 or 4) so biting the bullet and replacing them sounds like the way to go.  Nothin but money, honey! 

My files get dull for two reasons, use and using dental filling for low nut slots.  Even though the amalgam is UV cured I get a bit of gumming on my nut files.  Been planning to give them an acetone soak and see how that does with the clogging.

By the way and not to high-jack some of the sources that we've used in the past for Grobet nut files are no longer carrying them.  Where are you guys getting Grobet these days?  TIA!

Maybe you could contact about a dealer.

From a few different gunsmithing articles I found, the trick to acid-sharpening files is using muriatic acid (commonly available at the big box stores for concrete work) and keeping an eye on the process while it works so it doesn't get too far. Maybe 15-20mins maximum.  

The finer the file, the fewer times you can "get away with it" so I'm guessing that nut files would fall into that category of once... or maybe twice, at best.

A name that kept cropping-up over & over, for reasonable and professional file resharpening, was Boggs Tool & File out of the Los Angeles area  

The rates looked very attractive if that was something that someone was looking to do.  (by the way, Hesh, they state that they're Grobet dealers).

Off to Lowe's for some muriatic acid... I'll give a report-back. 


Otto Frei has other useful tools and supplies. I've used them a few times and they have been fast and responsive.

Incomplete link won't load and their's not enough info to see which one's you're looking at.  Try tiny url?


Sorry can't get the link to work.

Just search for Otto Frei jewelry supplies.

They have the entire Grobet catalogue I think.

Glad to see that Muriatic acid and Boggs were mentioned.

Muriatic is pretty powerful for a novice to try - in about 4-8 hours with a strong concentration you can start ruining a file.  Any acid will do and the weaker the acid, the more control you have.  Citric acid works fine but takes a couple of days.  

Franks' comment about the front lawn is very interesting.

Also, Boggs will make even new files even sharper.  I have managed to fit about 12 of them in a flat rate envelope - must have weighed 3 pounds!!.  They come back as good as or better than new for a couple of bucks - not bad considering that a new, high quality file can cost mucho denario.  

And remember that in years past farmers and craftsmen made things out of old files (along with handsaws) because they were a very high grade of steel, some of the best you could find. 

Great trick, and now you can buy those old files at the garage sales 10 for $1 and get a couple shapes you can use out the batch.


(Note to self:  Don't go to Lowe's or Home Depot on a Memorial Day weekend, unless it's absolutely necessary!)

Anyway, the muriatic acid bath seems to work but a little immersion goes a long way. The finer the file, the less am't of time is needed.  I used it on a particularly-worn .044" file that's been "dead" for a long time and that file now cuts!  Oh, maybe not as good as new, but at least it's usable again. 

I used the acid straight from the bottle (no dilution) and checked it after 5mins.... the acid had discolored and there were bubbles present, so it was doing something but the file was still dull.  After another 5mins or so, I took it out and rinsed it well and ..voila'... it cut a slot in a nut blank!  

Now the goal is to continue experimenting to see if extending the time will help with the sharpening (it should)... but at what point it becomes counterproductive.

Safety points: yes, the fumes are poisonous and for that reason (as well as protecting any ferrous metal nearby) it's worth doing outdoors. Vinyl gloves are very helpful.

Now I'm anxious to gather-up some old general purpose files and see what sort of trickery can be done! 


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