Can you sharpen a dull file in Acid? Sharpening metal files - Experiment

I've heard that you can sharpen dull files in acid. In this video I'll be experimenting with sharpening some in sulfuric and acedic acid.
Please consider supporting me on Patreon. www.patreon.com/user?u=58360840 You'll receive access to Patreon only posts as well as any 3d printing files that I designed.
Casting equipment
Melting pot amzn.to/3OeyeiI
PetroBond amzn.to/4bZJqsJ
Crucible salamander amzn.to/4eo1vSW
Crucible lifting Tongs amzn.to/3Vtc26G
High heat Gloves amzn.to/3XqPiai
Leather Jacket amzn.to/4chpUaU
Boot Covers amzn.to/4aZ1G4o
Boots amzn.to/3XpFmxz
Casting Flasks amzn.to/3Rtj4XT
Graphite Molds amzn.to/3VkiIUK
Blow torch amzn.to/3z3Rkms
Respirator amzn.to/3zbFUNq
Face shield amzn.to/4b47XM3
ToAuto Furnace amzn.to/4epMeRz
Propane Furnace amzn.to/3yVQIz9
3d printing FDM
Filament amzn.to/4coyVPQ
3d printer Ender amzn.to/3L58YsZ
3d printing Resin
Siraya tech castable resin amzn.to/4b95n7w
Elegoo resin amzn.to/3XrASGY
Resin Printer Mars 4 amzn.to/3RsL6mw
Belt Grinder
Grinding Belts amzn.to/3RsTySM
Surface conditioning belts amzn.to/4eicD41
Trizact belts amzn.to/3RuW0bg
Belt Grinder Accessories
Grinding Belts amzn.to/3RsTySM
Surface conditioning belts amzn.to/4eicD41
Trizact belts amzn.to/3RuW0bg
6” grinding wheel amzn.to/4b3NF5h
Welding
Kidskin welding gloves amzn.to/3VstSXu
Prime Weld machine amzn.to/3KMeXCQ
Metal finishing tools
Nevrdull amzn.to/3XwyVsu
Liver of Sulfur amzn.to/3XkFCOs
Protectaclear Clear Coat amzn.to/3XrBjkA
Scotch-brite Wheels amzn.to/3KI6v7B
Metal Files High Quality amzn.to/4eifrOB
Die grinder discs Benchmark abrasives amzn.to/4esof4v
Dremel - rubber polishing bits amzn.to/3KKvAi5
Dremel - Wire brushes amzn.to/3yYtQiu
Simichrome Polishing Compound amzn.to/3xapnZM
General
Wilton bullet bench vice amzn.to/4ckifIV
Bandsaw blades amzn.to/3XkmGPT
JB weld amzn.to/3xapGno
Super Glue amzn.to/3VISP2i
Shop Lights amzn.to/3xmMVur
Loc-line shield amzn.to/45v7Nfx
Smoke purifier amzn.to/3XoCMI4
Some of my favorite tools of the year
Makita Blower amzn.to/4c43LNK
Mini circular saw amzn.to/3VnWykp
Makita blower small amzn.to/4eCxFKT
Ratcheting screwdriver amzn.to/3KQUc8J
German pliers amzn.to/3xiRKou
Dremel cordless amzn.to/45ofDrt
Camera Equipment
Canon 6d II amzn.to/4erxUbi
Lights amzn.to/3xjzMSK
Rode Mic amzn.to/3XkFkHm
Canon 50mm stm amzn.to/3VJ3EBu
Canon 24-70 f2.8 amzn.to/3z340dn
All of the links above are affiliate links. This means that, at zero cost to you, I will earn an affiliate commission if you click through the link and finalize a purchase.

[@robinson-foundry]

If you're interested in any of the tools or equipment I use and you want to help support the channel then don't forget to check out some of the affiliate links in the video description. Thank you for the support!

[@Charlielizard]

After all my college chemistry courses and oilfield work, sulfuric acid is something I keep away from. However, the vinegar method looks like it worked great; and inexpensive as well. Appreciate the video.

[@unperrier5998]

H2SO4 is a bitch but far from the worst acid that exists out there. Remember that it's all about how you handle the risks... every year many people die in just H2O!!!

[@robinson-foundry]

I really wasn’t looking forward to using it and I’m glad I don’t have to anymore.

[@Convolutedtubules]

@@sergei693 Can I ask, when did you learn this trick with citric acid?

[@nancycurtis7315]

I use 100 grams of citric acid to 5 litres of water for restoring old tools. It works very well. A soak overnight and a brush off with a small scrubbing brush. Dry and spray with a lubricant. Been doing this for 5years. Greetings from Dimboola, in Victoria, Australia.

[@supernova874]

Yea same think for me too i let them in the solution overnight and the morning cleaning them and no more rust :) after that some lube and all good :)

[@nancycurtis7315]

@@supernova874 Cheap. Easy. Effective. Greetings from Dimboola, in Victoria, Australia 🇦🇺.

[@SadamHussain-58786]

😊

[@tonyowen8547]

Me too and it works well

[@dennisobrien3618]

I use powdered pH reducer for swimming pools mixed (imprecisely) with water. I think I heard of it from Master Smith Steve Culver. I believe he called it sodium hypochlorite; it's really good for removing forge scale too, and easy to store (less worry about spillage or fumes).

[@kenf4837]

I've been a machinist for many years and have heard about sharpening files with acid, but didnt want to have acid around where the kids might get into it! Never thought about vinegar! Im going to try it! Thanks!

[@unperrier5998]

Thanks. One measurement that you could have done is to file a piece of metal with say 100 strokes and measure the weight of the filings (by weighing the piece before and after) Doing that for blunt and sharpened files would be a good indicator of how much they're actually sharper. Project Farm did that just yesterday about sharpening mower blades.

[@StreetMachine18]

can confirm. i had a 5 gallon bucket filled with the finest walmart vinegar and i dumped all my garage sale finds into it. broken hammers, files, wrenches, etc. and they all came up aces!!! I recommend you try it at home.

[@vaultboy2270]

While really interesting I would have loved some kind of metric test, i.e how long it takes to file down X amount of Y before and after. But great vid :)

[@robinson-foundry]

Thanks. In hindsight I probably should have done that but I wanted to focus on really up close shots of the teeth. There are tons of videos out there showing this process but they don’t show the teeth up close. Maybe I’ll make a follow up video.

[@josphe9011]

@@robinson-foundry Please do!

[@ahab145]

Is the follow up video still planned to be made?​@robinson-foundry

[@BrilliantDesignOnline]

Super interesting. I did a railroad spike in vinegar and it helped; I have whole drawer full of files that now are going to get this treatment: Thank you.

[@Serbianguy432]

This video was very interesting, and as a guy who has, and uses, many files, I'll definitely be putting this in my bag of tricks for the future.

[@NP-rh3dt]

This is a great little video. I love the foundry content but I think you should do more videos like this as well. It's really such a shame that there are no American made files any more. Restoring old ones is the best we can get and I was really surprised how well the vinegar worked. I'll start hunting for files and restoring them since it worked so well.

[@alanchapman6170]

Phosphoric acid works well. Learned this many years ago ( 40+).

[@stefanmeyers2808]

Thanks for the video it was nice to see the difference between sulfuric acid and vinegar. you didn't mention how the end of the file turned out that you purposefully dulled.

[@masterimbecile]

Tangent question: after you do a casting project, what do you do about the charred sand? Do you scrape it off and toss it, or do you mix it back into the undamaged sand? Is there a point where the sand has too much charred sand that it becomes unusable?

[@SamanthaLaurier]

I'm also interested in knowing this so I'm leaving a reply to find out

[@noobFab]

Plus one for tips on re-using petrobond

[@MasterThief117]

Petrobond can be used until the oil has burned away. Once that happens, you can use a few methods to rejuvenate it, all of which requires "mulling" it with new detergent-free oil. There are a few videos on KZbin how to do this and also some on how to make your own for much less than Petrabond.

[@robinson-foundry]

I scrape off the black sand and keep it separate. It’s a pain but it’s the best way to keep the unburnt sand as fresh as possible. Once enough of the black sand has accumulated I rehydrate it separately with non detergent air compressor oil. You can mix it back in but the more you add the weaker the sand gets. So yes, you can mix it back in and use it many times but the fresher it is the better it will hold together. I’ve been meaning to make a video on this.

[@masterimbecile]

@@robinson-foundry Thanks!!!

[@silentferret1049]

Vinegar dissolves rust and cleans a lot of other stuff off of steel and iron. It does not like to dissolve steel or iron but it can embrittle hard steel so not a good idea for files. Vinegar does like to strip zinc and aluminum off of anything so if you have a layer of Zinc you need removed then that will work. Only problem is after Vinegar bath, it will rust up super quick. You would need a high concentration of Vinegar to start dissolving steel in any sort of way.

[@thespacenoob4760]

I'm impressed by how well it worked

[@Sammy-dz2hk]

This video is criminally underrated, have an algorithm comment

[@geuis]

Wonder if an ultra sonic cleaner would help with the debris removal vs having to manually scrape everything that thoroughly.

[@robthompson8285]

Thank you. I acid etch knives and these look perfect.

[@Convolutedtubules]

It's far more efficient to use a file card like in the video. But I think ultrasonic cleaner would shorten the etching time required, therefore minimizing damage to the file.

[@GreasyLuckForge]

Thanks for the video. I am always using files and looking for good old ones. I know you can have them sent out for sharpening, and I know they do it in some sort of acid, but I have never tried a test like you did. As others have commented, it would be nice to see a before and after comparison test of how they work. I may have to try that on my own. The white vinegar seemed to work well.

[@adrianwright8685]

I can see that acid might will clean out the dirt and rust. But it will also presumably remove a surface layer including from the teeth tips which I would have thought would blunt rather than sharpen. Might give the initial impression of being sharper but I'm not convinced.

[@ChrisEbbrsen]

Im an illustrator and need sharp files to sharpen drawing leads so this was reLly helpful thanks

[@WaddedBliss]

If you're in the UK patio cleaner contains one of the acids - I can't remember if it's sulphuric or hydrochloric. That would work on this. Patio cleaner also removes the galvanized zinc coating from metals if you need to weld them.

[@CarlWestBlacksmith]

Patio Cleaner in the UK might be what we Yanks call Deck Brightener. If you get the stuff that is oxalic acid it's great for rust removal. Might be a nice clean-up step before the vinegar etch.

[@DanielEngsvang]

Great initiative!. I will try with the acids i have at hand as Sulfuric acid is quite hard to get your hands on here in Sweden(People making Nitroglycerin i guess). Rusty files with very fine teeth are impossible to clean with a brush so they are going to have a bath tonight i suspect. 🙂😇😄

[@liebetrau88]

File card** Also, not sure if this actually makes them sharper. The "dull" spots you talk about are burnished areas of the file, which is why they are shiny, that have been rounded over. Removing material via acid etching will, in theory, make them sharper, but not by much. However, what the acid will do, will leave a very even surface finish as it erodes away on every surface, thus removing the burnishing and leaving a consistent finish.

[@martylawson1638]

If the "dull" spots are anything like I've seen happen to band-saw and hack-saw blades, the burnishing leaves a burr hanging forward on the cutting edge that moves the sharpest point away from what you're cutting. Sounds like dissolving this thin burr is enough to restore the cutting power of the file.

[@Convolutedtubules]

Maybe the acid clears off any foreign metals that may have adhered to the teeth, that probably helps a lot. By etching a flat piece of hard steel, you can create a fine-grit file, the metal grain texture will act as an abrasive.

[@Convolutedtubules]

A long time ago, a man displeased his woman by using her wool card to clean his metal files.

[@liebetrau88]

@@martylawson1638 if it was a thin burr, then the file card would have likely removed it.

[@liebetrau88]

@@Convolutedtubules those foreign materials would have likely been removed by the file card.

[@noneyabidness9644]

I use vinegar to sharpen my files. It works. Been doing it for several months.

[@TheDavidlloydjones]

What a wonder to find out about all these marvellous industrial liquids are out there on the market -- and whata pleasure to find out that vinegar works so well.

[@Tann114]

Great video, I loved when people explore and test things for themselves. I wonder how good just soaking them in water for 40 mins is.

[@markrowland1366]

A saw doctor, like my father, an eight year trade, went through many boxes of files a week. All mill files flat with diagonal fine cut. To his eye they were dull but I had a plentiful supply. He once hit the jackpot, fileing perfectly allowing the saw to cut for two weeks . The angles were true and the tips within a thousandth of a n inch. When a big circular saw blade spins up it stretches, creating a dish shape. He had special large hammers to prepare for that, looking down from above, the centre , amazingly could flop left ro right when shaken. he ended up being the biggest timber man, 12 sawmills, a trus factory and a pallet rental which he sold, becoming Chep, now with twelve million .

[@chrisfournier6144]

My experience is that you can refresh a good file that is barely dull. Make an 8/10 a 9.5/10. However, the first file that you showed is shot, acid won’t bring back a used up or abused file. If you’re using acid, I’d recommend that you do this outside of your shop unless you like rust on all your tools and machines.

[@johannaverplank4858]

I’m gonna have to give that a try on my files. Thanks for sharing!

[@doncallicott1696]

What about the file tip you intentionally dulled?

[@workingguy-OU812]

Yeah, did I miss the outcome of that?

[@doncallicott1696]

​@@workingguy-OU812I did like that video...probably will be using the vinegar, lot's safer.

[@BMWHP2]

Thanks for your work and time. And thanks for sharing the knowledge with us. I will do it with my files.

[@williamlanphar630]

I am glad to have learned this, thank you

[@AndiNewtonian]

Very interesting! I use vinegar to dye wool, so I was surprised to learn that it's strong enough to dissolve steel!

[@drstrangefart]

Answering the questions I didn't know I needed to ask. Cool video.

[@Dino_Buk]

Only thing I find that will sharpen the file to be sharp as a brand new file is HCL / Muriatic acid. Just don't forget to neutralize the acid with baking soda for about 1 hour since it's a very strong acid.

[@salimafridi2304]

Dear sir , i have 60 dull files and i dont know what to do with it , will you plz tell me wht is HCL? and wht will be the ratio of backing soda and acid? thanks

[@causewaykayak]

​@@salimafridi2304Hydrochloric Acid chemical formula. Muriatic Acid is an archaic name - scarcely used today. This acid you could buy from plumbers merchants. Amongst other things it is used for cleaning off dried-on cement splashes. Wear gloves and eye protection.

[@Mark-oj9to]

You can purchase vinegar that's up to 16% acetic acid. Will do a fantastic job.

[@marcelgongora]

A method I learn from my grampa, who was farmer and has to deal with this in the 70s (not in USA) without acid or vigager. Lemon or grapefruit juice for several days. It will have similar effect than the vinager from this video.

[@MrBillmechanic]

excelllent!!!! willdo thismyself on my files.!! I plan to fry this with chian saw files, but thismust be done carefully inor der to avoid undersizing the file diameters. I will firstmike the file, hold iin white vinegar for anhour. Mike it again to detect change in diameter. Thenfor anotherhour, testing file sharpness along the way.

[@randalc6118]

Just one question what was the percentage of acid in the vinegar. Normal vinegar is 5% where as cleaning vinegar is 10%.

[@dimoradimario]

With citric acid this should work well too. It also acts as a rust remover.

[@nicholas_obert]

Or if a file is too dull to be sharpened this way, you can always turn it into some other tool. Knives and chiesels made from old files are a common option. The teeth might be ruined, but there's still a lot of good high carbon steel in there.

[@ersetzbar.]

you realize he told just at the start of the video thats the very reason he collected those?

[@angieandfidelromero9343]

Very nice! I’m going to try this! I enjoy your videos. How much would you charge for a Coca-Cola bottle casting in brass and another in aluminum?

[@dhcoloniemain9358]

It looks like acid cleaned the files, but did it actually make them sharper? If they were dull from bent-over metal, how did the Acid fix that? I do think that degreasing, using a file brush, removing rust, and then acid-treating files is a good thing though.

[@cyrus7210]

Give this a shot for cleaning. Look up electrolysis method for removing rust. Simple,cheap,safe(follow directions) and does a great job of cleaning the crud out of files. Great for tool rust removal.

[@FarmsteadForge]

Very interesting, thanks for the video! I use a sisal wheel and compound to sharpen my farriers rasps. It works well but you have to be on it from day one.

[@CarlWestBlacksmith]

Intriguing. Do you hold the rasp a particular way against the wheel? It seems that doing it wrong would dull the rasp.

[@FarmsteadForge]

@@CarlWestBlacksmith I make sure the wheel spins with the angle of the teeth, not against it.

[@AivoPaas]

Files saved successfully.

[@wisterialosenge2546]

haha i put some greasy car gears from an 80's car in some toilet bowl cleaner to get the grease off, left it in too long and there was barely any gears left a couple days later, it was just a chunk of rust remaining

[@Markozmajar]

The question is, is it sharper or cleaner? It cuts better for shore after the process but, I never saw a guy or girl to sharpen the kitchen knife with vinegar or acid. If acid eats material away, the tips (cutting edge) would be gone first.

[@BasedBidoof]

Cool, I'll have to try this

[@warrenozblod8594]

@Robinson Foundry I don't mean to impose, but do you have a affiliate link to the thick-walled glass beakers you were using. Or a name? Thank you for the great content

[@robinson-foundry]

I wish I had a link for you. I bought them at my local thrift store. I got lucky and found just the shape I was looking for but any tall glass vase should work. Thanks!

[@davidsalman8362]

Have you ever tried Talcum mixed with Engine oil as a Casting sand instead of Sodium Silicate sand or Petrobond? i'm thinking of trying it, let me hear your thoughts

[@lizliz7075]

I just throw them in vinigar for a couple of dsy. Weak acid but i still works well. And cheap. Keep a plastic container with a lid and throw anything you want to ddrust into for a few days. Rinse in hot soapy water. They wont be shinny they will be cold blued. Oil and smile. No need to neutralize in vinigar.

[@rickburris6164]

I was just curious, have you made anything out of "pot metal"? Monopoly game pieces and cap guns come to mind but all sorts of engine parts and toys were made of pot metal

[@martinwyke]

Great test, grat result.

[@piconano]

Never thought of that.

[@AKATONA1953]

You may try 2% citric acid. It is the safest and does not attack the steel itself. It is widely used for similar purposes in industry.

[@ungodly_athorist]

How did the part that was super dulled at the tip turn out?

[@autumn5592]

I dont know why he skipped it either. Probably because the results weren't great.

[@Rick_Dunaway]

can you strain and reuse the evapo-rust or how does that work with that product?

[@smallshoptalk589]

WOW, I need to do this. Thanks.

[@zachary_fb]

I've heard aqueous Ferric Chloride works as well

[@SolarinDay]

*puts on my Vulcan ears* Fascinating.

[@unperrier5998]

how about you put your Vulcan useless comments on OFF.

[@adrianwright8685]

Hot acid/vinegar would make for a quicker reaction - just try heating it up before using. Surely could wash the acid off with water - don't need an alkali?

[@robthompson8285]

Man, I love your videos! Always so fascinating and entertaining 😊btw where did you get those large glass cylinders?

[@dionh70]

Those look to me to be flower vases from a craft store like Michael's or Joann's or something similar. I've also seen similar vases at the dollar store occasionally (pure hit-or-miss), Big Lots (again, pure hit-or-miss), Ross Dress For Less, and so on.

[@nightowl5401]

great information going to try it thanks

[@CoalCoalJames]

Nice, I got a couple of old round files that I was gonna throw away or use as random metal fro projects. I don't know why this slipped my mind, we used to clean metal with vinegar all the time when I was young (or coke).

[@Convolutedtubules]

Maybe the acid clears off any foreign metals that may have adhered to the teeth, that probably helps a lot. By etching a flat piece of hard steel, you can create a fine-grit file, the metal grain texture will act as an abrasive.

[@KewlQT]

Do you ever try cleaning your files with a card file first? Or even a regular wire brush to clean out all the impacted debris. I wonder if heating the vinegar on a stovetop with it in a glass pot would increase the momentum of this process. Has anyone tried out testing this method with an old file? Since you mentioned the sun warming your vinegar solution seemed to speed up the process gave me this idea.

[@buffalojones341]

It would’ve been nice to see you take five or 10 strokes on some chunk of mild steel, before and after, using the same file.

[@jeremynedrow7003]

I always use vinegar to clean metal. It works great.

[@Kevin-is-here]

Is muriatic acid too strong?

[@kevinleee3408]

My dad uses muriatic acid to clear rust from his WellPoint I wonder how that would work on files

[@gray1034]

Biggest takeaway is vinegar is one of the least expensive and best rust remover, but it will not sharpen and worn out file

[@stefanmeyers2808]

Make a video to prove your statement.

[@webwizardofoz1162]

huh, what happened with the end bit you dulled?

[@pmedic523]

How many times could you use this method to resharpen files before the files become unusable for whatever reason?

[@unperrier5998]

good question. fancy experimenting yourself and sharing your findings?

[@pmedic523]

@@unperrier5998that would be fun to do and figure out but I’ve got such a to do list for the house I’ve got really no time for anything else.

[@bluaugendvl]

​@@pmedic523Yet you're here on KZbin watching how-to videos instead of getting those to-do list things done 😮 Ha ha, just like I am! 😄

[@notfeedynotlazy]

2:14 *Kids doint this at home, remember to **_always_** do it as he does here!* _ALWAYS_ pour sulfuric acid to water just as he does. If water is poured onto sulfuric acid instead, you risk an _actual steam burst blowing acid everywhere_ - your face being a prime target, already on the line of fire. Something worth saying ALWAYS. (If you wonder why "water on acid" goes _boom_ and "acid on water" doesn't, it's actually simple: as the pure acid mixes with the water, it generates a bit of heat. If you add a bit of acid to a lot of water, you have little acid trying to heat a lot of water (duh!) and nothing spectacular happens; but of you pour the water on the acid, the very first drops to fall are a bit of water with a lot of acid, generating a _lot_ of heat on a ting ammount of water, potentially _turning those first drops into steam_ - which will gleefuly blow tiny droplets of concentrated acid everywhere). Source: years of handling acids and an actual laboratory acreditation on my name.

[@avianfish8732]

So it works? Why?

[@toolthoughts]

are you worried about embrittlement?

[@MASI_forging]

Thanks for sharing. 👏👏

[@jdmccorful]

I like the white vinegar concept. Thanks for your time.

[@adarshsharma8436]

What happened to the file that you deliberately dulled it?????

[@markhuyette8509]

You should boil them in vinegar works real good an old timer told me that when I was a kid

[@kevinleee3408]

If you own a pressure washer you could fasten the files to a board and possibly save some brush work.

[@garetz2011]

I remember my father doing the same in 1980. He used something like "deactivated acid". I can't recall if that acid was deactivated with zinc or aluminum... I was twelve and I don't know a shit about chemistry. But the file became much more aggressive. I need to remove aluminum from old files and copper is not working. I read muriatic acid may be the solution to dissolve aluminum without harming the steel.

[@scottrobinson1564]

It seems your just removing rust and crap, I suppose that will sorta sharpen them. Probably the same as a wire wheel..good idea about making knifes! I didn't know about that. Going to try it out..my last name is Robinson. You get a sub and like from me Brother!

[@LSeverusPertinax]

add plenty of table salt to the vinegar.. it speeds the process.

[@PalmerstonIslandCicc]

I used to squeeze lemon juice in a bamboo and dip file in it..new again

[@L1mJahey]

Reminds me of that episode of The IT Crowd...

[@RyanMercer]

Nice.

[@samthesequel]

2:18 those look like very tasty beverages

[@doriWyo]

I don't know about file appearance, but they didn't sound like they were doing very m7ch.

[@markzambelli]

I've got some old files on a Hard Drive I keep by the computer... the Sulphuric Acid has now completely destroyed them😮‍💨

[@einfelder8262]

There is a much easier and less messy way to sharpen dull files. You can lay your hands on them and pray, which gets the job done in a flash.

[@carrestore]

good job 👍👍

[@Bhartrampf]

Muriatic acid works well also

[@nigelsmith7366]

Lemon juice works as well.... Just don't leave 100mm files in it for 7 days🤣🤣🤣😭🤣🤣🤣... Time to buy new files for me 😆😆😆

[@CoalCoalJames]

True, coke or lemon juice is great if ur out of vinegar or industrial acid.

[@unperrier5998]

@@CoalCoalJames phosphoric acid (coke) is more potent than sulfuric acid, although it's far more diluted in Coke.

[@yoyoramos7909]

Thanks 🙏

[@samsawesomeminecraft]

I'm curious about the geometry of this process.

[@stefanmeyers2808]

A squared plus B squared equals C squared. The teeth are triangular in shape.

[@gray1034]

The shiny spots are the teeth of the files broken and smashed down, from back and forth action files only cut in one direction.

[@jumpemupjohn]

thanks

[@MrRogsmart]

What Charlielizard said. Thanks.