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I have accumulated quite a few old files over the years. Some are not very effective, but I have never thrown them out. I have tried cleaning them with wire brushes and have even tried solvents, but without much improvement.

Is there a way to sharpen/restore old files?

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    When I first read the title I came fully prepared to leave a comment telling you to ask on SuperUser instead. – Jason C Mar 6 '16 at 4:55
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    @JasonC Do they deal with old manilla folders as well? – Ashlar Mar 6 '16 at 15:36
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    Before files became a throw-away item, there was a whole industry devoted to re-cutting and resharpening them. This book by Disston gives a good history of the tool. – grfrazee Mar 7 '16 at 20:21
  • @JasonC Lol me too – William Mar 8 '16 at 14:33
  • @JasonC I thought the same thing. LOL! – user148298 Mar 22 '16 at 17:59
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Is there a way to sharpen/restore old files?

Yes. The classic old method to sharpen a file is vinegar sharpening which is exactly what the name suggests, soaking the files in vinegar.

Now that we know the active ingredient in vinegar is acetic acid we can make the obvious educated guess that it's an etching effect from an acid. And it is known that other acids do the same job and were used in the past. Two of the best alternatives because of easy access are citric acid and sulphuric acid (e.g. battery acid). It's best not to use hydrochloric even if you already have some, many sources speak of the risk of hydrogen embrittlement when using HCl so it's best not to risk it since files are already brittle enough.

Acid etching works best on files where they are not heavily worn but are just rounded from use and no longer cutting well. Where there is any scoring/scratches or the teeth are worn down so far that there are flat shiny patches (hard to believe but you do occasionally see old files that had been used that hard!) you won't recover a usable surface. But files are nearly always double-sided and because this is inexpensive and largely a hands-off process that mostly requires patient waiting it can be worth it for a file even if it only has one side worth salvaging.

Degreasing
You say you've used solvents and that is one good way to start the process off as a file must be thoroughly degreased before soaking in acid to give it unimpeded access to the metal, ensuring even results.

In addition to organic solvents you can also soak in oven cleaner, or a hot solution of washing soda. Both will eat any form of grease and pose no harm to the steel.

If you want to use solvents I wouldn't rely on mineral spirits/white spirit alone, soak in spirits to begin with then dry off and brush down or soak in acetone or lacquer thinner.

Cleaning
If the files have any clogging this should be removed before etching, again to give the acid full access to the surface of the file.

In addition to using a 'file card' (a type of brass-wire brush specifically intended for cleaning swarf from files) there are other methods, including pushing in the direction of the grooves using the corner of a scrap of hardwood or the edge of a piece of brass. But some material clogging files can be very tenacious (a good example is aluminium) so you will sometimes have to resort to picking bits out of the teeth patiently with a needle or another sharp steel tool. If using a needle your hand muscles will thank you for chucking it up in a pin vice or permanently mounting it in a wooden handle rather than just gripping the needle in your fingers.

This picking away is just as tedious as it sounds, and can take anywhere from a few minutes to an hour of concentrated work per side, but it's worth every second of the effort.

You may want to quickly degrease a file again after cleaning, especially if you've done the work with bare hands.

Note: you can clean first prior to the degreasing step, but I've found that clogging residue (esp. wood) can be much easier to remove from a file that was thoroughly degreased first, and it's easier to see it all anyway.

Rust
As you might expect if the file is rusted soaking in acid will simultaneously clean the rust from it, so this is a very useful technique for secondhand files picked up from various sources since you'll clean them of rust while also improving how they cut. But don't expect too much if the file has any heavy rust encrustations, after the rust is gone some pits can be left behind. While on some tools pits can be merely a cosmetic issue on files they can impact performance, in the worse cases leading to irregular abrading of the workpiece or scratches.

After soaking in vinegar or another acid even after rinsing thoroughly the files may start to rust again very quickly (flash rusting) so it's advisable to give them a quick spray of something like WD-40 immediately after to help halt this process.

So here are the steps:

  • brush off any loose matter
  • degrease
  • clean off all debris
  • degrease a second time if thought necessary
  • soak in your chosen acid*
  • rinse thoroughly then give the file a quick scrub with a stiff brush (a toothbrush is ideal) using common hand soap
  • pat dry
  • shoot with WD-40 or another water-displacement agent, or dry thoroughly using a hairdryer or by placing in a warm oven

*No real guidance can be give on the time needed to soak a file. Using vinegar for example while you can typically get some improvement with just an overnight soak, with some vinegars, on some files, you may need to soak for two or more days before you judge it has done all it can.

The strength and concentration of the acid being used, the coarseness of the file and the amount of wear all have a huge impact on the time needed. So for stronger acids on finer files you may want to remove them from soaking after just an hour to check progress, with a weaker vinegar on a coarse file leave overnight to begin with and expect that it might take much longer to achieve the desired result.

When the process is completed the file should be quite uniformly dull and grey, and rubbing a thumb over the teeth it should feel very 'grabby', much more so than many files are straight from the factory.

Here are some self-explanatory pictures of the restoration of some files I bought last year:

File restoration 1 File restoration 2 Files soaking in vinegar

And here they are with the work completed, with handles:

Shellacked file handles

Note the characteristic dull grey appearance of files treated this way.


Commercial sharpening

There are commercial file-sharpening operations out there in the world and some people rave about the quality of the work. Some users are so impressed by the results — often stating that files treated this way are sharper than any you get straight from the factory, irrespective of cost — that they buy new files and send them straight to be sharpened before ever being used.

It seems fairly certain that these companies don't do any sort of re-cutting of the file teeth as one might first think, but instead they all use some form of acid etching. Although they may have any number of additional steps (including post-etching treatments to improve rust-resistance) there's no reason to suppose you can't get results similar to or as good etching your files at home in the manner described.


  • See rust removal discussion for explanation of why acetic acid in particular works well to remove corrosion from iron: iron acetate is soluble in water. – keshlam Mar 6 '16 at 23:12
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    @FreeMan, washing soda is sodium carbonate. It's actually sold as "washing soda" in most English-speaking markets. In the US Arm & Hammer's version is widely available, in the UK the Dri Pak brand seems to be the most common. – Graphus Mar 7 '16 at 20:16
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    ...so it is. Huh. Learn something new every day. – grfrazee Mar 7 '16 at 20:22
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    @JasonC, it is definitely a restoration process and not just cosmetic. You can feel the difference distinctly by rubbing your finger over the file, towards the tang. Much more bite. I doubt you could dissolve enough metal in any reasonable timeframe to make the file's surface smooth, but yes you could certainly soak for too long (particularly an issue with stronger acids obviously). Over-soaking can lead to the file being brittle and wearing far more than it should in use. – Graphus Mar 8 '16 at 16:27
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    @RobSiklos As long as it takes for how greasy the file is. As this won't harm steel it's OK if you leave it longer than the file actually needed. Rough guidelines, 1-2 hours for slightly oily, 6-8 for greasy and half a day or overnight for any that are really caked with dirty grease. – Graphus Dec 13 '17 at 7:38
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To me it looks more like a blacksmithing-related question.

One option would be to heat them in order to hammer them to a new blank shape, then to make them cool down in ashes for the metal to be soft. Then to cold-chisel them with the grooves you need. Finally to heat them again for hardening to quench them and to temper them. There is a neat video that shows how auriou rasps are handmade (french sorry) : Youtube Auriou rasps

I didn't try it myself now but definitely will do it at some point :)

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    Right :) I can't wait to set up my own smith shop in the basement! However, the video was great. Surprisingly, I was able to understand everything even though it was in French. And they are so reasonably priced! Thanks for the link. – Ashlar Mar 20 '16 at 1:28
  • BTW welcome to Woodworking.stackexchange – Ashlar Mar 20 '16 at 1:29
  • Thanks :) It is still a bit strange to me to not ask computer-related questions here tough :D – Joel.O Mar 20 '16 at 1:32
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Ferric Chloride (III) can be used also. But it's better to purchase a new file rather than to refurbish it.

  • "But it's better to purchase a new file rather than to refurbish it." I can't see that this is true overall, as my experience and that of many others does indicate a re-sharpened file can perform superbly, possibly even better than when it was new. As well as that many older files would actually be much better quality than current production today. This is even if from the same maker — best example might be Nicholson after they shifted production out of the US, but there are some others including Grobet. – Graphus Mar 7 '16 at 14:17
  • But it's better to purchase a new file rather than to refurbish it. Not the crap files that you can buy at a big-box store these days. I'll take a cleaned vintage file over one of those any time. – grfrazee Mar 7 '16 at 20:11
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There is a simple answer but expensive. Dremel.

This tool is specifically designed for reconditioning all tools. It even sharpens chainsaws should you need it. It is a delicate multitool for lots of applications including (but not limited to) engraving. This option may cost more than a wiring brush, but if you are into investing into tools it is worth the workbench it sits on.

There are cheaper such power tools that you can inquire about at a local DIY for a lower price. They deal only with cleaning tools.

The final option I would suggest is getting a wire brush for a power drill. I've used this to clean rust off of metal. It's fast and fairly easy if done right. Attach the piece to a work surface then use the wire brush bit to clean everything. The more build up you have the more it may take.

  • I'm not clear on how you would use a Dremel to clean and sharpen a file better that a wire brush and solvents. – Ashlar Mar 17 '16 at 1:37
  • It comes with mini wire brushes. It can rotate at speeds you set giving you the ability to set fineness. The brush is small giving it more small precision. As well it comes with small grinding stones to sharpen it. It's an expert solution, but giving you might be interested in old it is better. If you are looking at selling them as antique this would be a horrible idea however. – Frank Mar 17 '16 at 1:42
  • Given the speed with which my variable-speed Dremel spins, even when set to its slowest setting, I'd be quite concerned about attacking a file with a grinding wheel and ending up with a large flat spot. If the Dremel were bench mounted and you had a jig of sorts to hold the file in place and move it precisely along the multitude of edges, I could see that possibly working. Freehand just seems to be a disaster in the making, though. For the initial wire brushing, I can see it working, but I'd think a slower turning drill would be better there. – FreeMan Mar 17 '16 at 12:55

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