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Thread: Metal files 101

  1. #136
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    G'day Jim

    Go to the cooking section of Safeways (Woolies up here), and with all the McKenzies brand Bi-Carb soda etc, you'll see Citric Acid in a 75g cardboard cylinder. I think I paid about two dollars. I used 35 grams in 350 mls water, about 70-80 degrees.

    You'll see a nice stream of bubbles coming off. Give it it a swizzle every now and then. Time will depend on how robust the rust is!

    I took them out, washed them, dunked into a 10% bicarb bath (prolly not necessary for an acid of this strength). You'll then find that they have a dull grey residue on them. I brushed this of with a brass brush on the flutes, and a s/s brush on the shank. These brushes were the "Medallist" crap variety, and the wires are about 0.18mm thick.

    Matter of fact, I'll just go down to check the second batch.............

    ............yep, just as I thought. The second batch have NOT had the grey residue brushed off them yet, and there is NO new rust. This residue is exactly the same as you can see in the picture of the new file, but has formed while they were in the Citric Acid. It's a PITA for coming off onto your hands etc, but it does seem to prevent rust.

    Does anyone know what the residue would be?
    Iron something or other.

    Cheers, FF
    Regards, FenceFurniture

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    Does your residue look like the second pic in this post?
    link HERE

    Thanks for the info on citric acid BTW

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    Exactly like 3rd pic post #111, and first pic 125. And yes, vinegar gave the same residue.
    Regards, FenceFurniture

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    "One last argument, so obvious that I've never thought about it before. If acids can sharpen files, why files makers who dedicate their time and efforts to produce the sharpest possible files, do NEVER use this technique in their production process ?"

    With due respect I don't feel that is a valid argument at all. When searching through the internet on this topic I've come across many hundreds of different occasions of people claiming they have successfully sharpened files through the use of acid etching, and I have personally read through 20-30 of these claims in full. Apart from the fact that you're suggesting all of these people are mistaken, which can of course be a genuine possibility, I have not seen even one occasion where the person involved made any claim that the file was etched to create an "as new" sharpness. Indeed, as I have already mentioned, the general consensus is that using acid to etch the metal restores the file to about "80%" of the original sharpness, it allegedly does not restore it to new condition, miraculously repair damage, nor indeed do anything else being proposed, other than simply evenly etching metal from the file. Once again thereby causing the previously rounded tips of the teeth to adopt a sharper profile as outlined by Bryan with his diagram. If the apex of that tooth was already acute (ie sharp), in theory the very same process would actually somewhat dull an otherwise sharp file.

    That's the theory, and I haven't yet seen any discussions that even come close to refuting the theory behind it. Whether it works in practice is of course and entirely different matter. The considerable work done by FF would suggest in practice it doesn't, however as I pointed out, the fact the acid used didn't erode ANY metal does seem to raise more questions than it answers.

    Pete

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    I may well be raising more questions than I'm trying to answer!

    Last night I noticed that the grey residue didn't seem to come off on my hands as much (after a few hours out of the CA), so I left it overnight. I tried to find out on the web what the compound might be, but there always seems to be a missing link. The nearest that I could estimate it to be is Magnetite (Fe3O4) which is said to have a bit of rust resistance, but not a great deal.

    So, i got some hot water (about 400 mls) and dissolved about two teaspoons of salt in it, dropped the still grey drill bits in for a while, out to dry so rust could start, back in for a quick swim, dry, etc for four cycles over about an hour. On two of the bits I had used the small S/S brush on the last 15mm of the shank, before the salt bath. These particular areas have none to very little rust forming. The third (unbrushed) bit has a couple of quite decent rust areas forming (this would lucky to more than 3-4% of the surface area on a 125mm long bit. Another perhaps 8-10% has very light rust, and the rest of the bit (85%) is rust free.

    These variations in the rust pattern are to be expected of course, and are probably because the compound is thinner in those areas.

    But what about those lightly brushed ends? The grey res was reasonably uniform on the shanks, but the brushed areas show less rust. Have I somehow burnished the shank, or some bloody thing? Beats the hell out of me. The brush is the size of a toothbrush.

    The grey residue itself varies in colour from 50% black (mid-grey) to a rather nice charcoal colour, about 85% black. This is what leans me towards it being Magnetite, which does have a bit a varying in its colour.

    Whatever this compound is, it has to be from the following elements: Fe, O, H, C because they are the only elements present in the Citric Acid bath (C6H8O7).

    Man oh man - where's a Metallurgist when you need one?
    Regards, FenceFurniture

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    Out of interest FF, I've just retrieved that piece of exceptionally well rusted steel that I used for my own vinegar experient. Since that day, it has been sitting back in my scrap pile in the backyard where it has been rained upon several times. One side is showing some small areas of re-rusting while the other is still rust free. Interesting!

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    The first batch of Liogier Rasps was despatched from France yesterday, and included in the package are a couple of samples each of Saw Files, Milled Files and Engineers Files. Looking forward to checking them out in a couple of weeks.
    Regards, FenceFurniture

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    Default Crikey

    I just put in a post in all honesty asking if I could sharpen my old Dad's files, then got chucked out because they said I should read a 10 page post on file sharpening, so the only thing I got out of the post was to stick your file in acid! Sorry folks, I'm not talking about etching away your favourite old tools I'm talking about actually sharpening them back to as you would your saw blades, totally different thing, but what can one expect.

    Oddjob1

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    Quote Originally Posted by Oddjob1 View Post
    I just put in a post in all honesty asking if I could sharpen my old Dad's files, then got chucked out because they said I should read a 10 page post on file sharpening, so the only thing I got out of the post was to stick your file in acid! Sorry folks, I'm not talking about etching away your favourite old tools I'm talking about actually sharpening them back to as you would your saw blades, totally different thing, but what can one expect.

    Oddjob1
    Crikey indeed! Sorry Oddjob, tried to help by putting a link in for you and somehow I locked the thread.

    My abject apologies, I won't do it again (I hope)

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    Quote Originally Posted by Oddjob1 View Post
    I just put in a post in all honesty asking if I could sharpen my old Dad's files, then got chucked out because they said I should read a 10 page post on file sharpening, so the only thing I got out of the post was to stick your file in acid! Sorry folks, I'm not talking about etching away your favourite old tools I'm talking about actually sharpening them back to as you would your saw blades, totally different thing, but what can one expect.

    Oddjob1
    If not acid, what's your idea for sharpening a file? Grind one tooth at a time? With what?

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    Quote Originally Posted by Greg Q View Post
    I have a book here too from the department of skills and shortages on files. I am going to send it to RC to scan and add to the PDF collection.
    what PDF collection...where...where.... where
    whats in it...anything I may want???

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    I was speaking of the general online collection of PDFs. RC did a copy of my 1965 Sydney Machine Tool Expo catalogue which he has somewhere. Maybe he'll send you a link (which I no longer have).

    Greg
    It's all part of the service here at The House of Pain™

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    With refernece to Oddjob's question, the only sure way that I know to restore a file to a better condition is to use a flap wheel or surface grinder and do a light skim of the teeth. This will take off any rounded tooth tips but does not put clearance back into the file - it will cut but not as freely.

    Michael

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    Michael I have to say I'm struggling with this idea. I have rubbed a file on a fine bench stone to dull it for use as a burr file for scraping. It only took a few strokes to render it useless for normal duties. You sound pretty credible to me, and I can't see why you'd make it up, so I'll give you the benefit of the doubt, but it would have to be a very light touch is all I can say. I don't think I'll be trying it.

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    You're right - it has to be a light touch. I discovered this when I was preparing an old file to turn it into a scraper (and was sure I read something about it too but can't find the reference). It would not be worth doing with a small file or one with fine teeth, but if you have an old 12" bastard I'd try it with that.
    The way that I think about it is that a blunt file will have rounded tips on the teeth. By lightly touching with say a flap wheel you are removing the blunt bit of the tooth and leaving a sharp corner. The down side is that you lose clearance at the rear of the tooth.
    As I implied below it won't bring a file back to new condition but it will wring a little more life from it.

    (I am prepared to be proven wrong, but considering the majority of the thread is about soaking files in acid, I can't see that it is much more radical...)

    Michael

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