Sharpening files using acid: does it really work ?

Discussion in 'Castings, finishing/ repair/ and patina's' started by metallab, Oct 8, 2020.

  1. metallab

    metallab Copper

    I saw Youtube videos on sharpening files and I wondered how they did it. files

    Some use acid (sulfuric acid or even vinegar) but how does this work ?
    When the teeth are blunt or dull, I thing it cannot be chemically sharpened. Admitted, I did not try it out yet, but I have strong doubts about it.

    What are your ideas on this ?
  2. dtsh

    dtsh Silver Banner Member

    I have not tried any of the acid cleaning methods, but I think Mark L'Ecuyer (thatlazymachinist) has you covered with this, I think his steps 4 and 5 are key.

    The short answer for those not wanting to watch a video, if the file is actually worn out it's scrap, get a new one. If it's just fouled up with crud, go at it with a file card and carry on.
    Petee716 likes this.
  3. For those who are really keen, here's a description of how to hand cut files with a chisel. This was arduous piece work done by housewives in their kitchens in their spare time:

  4. dtsh

    dtsh Silver Banner Member

    Oh if you're going to go there, I think Clickspring has a good video on making files.
    Mark's castings likes this.
  5. Fulmen

    Fulmen Copper

    I share your doubts.
    Simple logic would suggest that the acid can only make things worse. If you strip a surface down evenly it can only become more rounded.
    Now it's possible that the acid won't strip the surface evenly due to the grain structure, but I think that's a long shot. But I'll have to try it one of these days, it's not like there's any risk to it.
  6. There is the principle of electrosharpening using strong acids and electrolysis, a bit like electropolishing but used on surgical scalpels.

    Here's a patent using a cocktail of acids including hexavalent chromic acid:
  7. GTS225

    GTS225 Copper

    I'm thinking that files aren't so expensive that I need to go to the expense and danger of forking around with acids. I'll just hand the dull ones off to a forger for knife blanks.

    Petee716 likes this.
  8. JCSalomon

    JCSalomon Copper

    Nope. Nopity-nope-nope. Uh-uh. No way. Let someone else do it.
  9. Fulmen

    Fulmen Copper

    Bah. At one time I handled kilos of the stuff at a time. It's the poisons and super-acids that you really need to pay attention to. And let's not forget the explosives. Or better yet the poisonous oxidizers (barium, lead, mercury salts), those are always fun.
    Say, did the coffee taste funny to you?
  10. spelter

    spelter Copper

    Horse puckey.
    Simple (ie uncomplicated in size and shape) molecules of acid attack from the outside in, smoothing all shapes.

    There are situations where acids can develop moretextured topology with time. MEMS, micro electro-mechanical systems, can be developed into elaborate shapes through etching, but it takes a resist applied to the high points of the finished surface, and an acid that is a large molecule with an eccentricly placed acid group. Say, a resist is applied leaving a square availible to attack. If an acid located at the end of a linear molecule is used as an etchant, a pyramidal recess can be developed. Pretty amazing. But a simple acid and no resist is not going to do anything but smoothing.
  11. HT1

    HT1 Silver

    Mark's castings likes this.
  12. OMM

    OMM Silver

    Oh boy. Fools gold. There is a distinct difference between cleaning a file and sharpening one. When the teeth are gone you can't re-sharpen them with any chemical. They are just garbage. Buy a new one for five dollars.
  13. Jason

    Jason Gold

    Sharpen files? Forget that nonsense... I'm more interested in ToT's last video. Tig filler wire for putting edges on stuff you want to sharpen????!!!
    Look out lawn mower blade! Here I come!

  14. TRYPHON974

    TRYPHON974 Copper Banner Member

    Never tried the acid but caustic soda can easily clean a file, a rasp or any tool gummed with aluminum. It's an old trick but it still amazes me to see how fast and easily it works.

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