Help me remember a file sharpening hint...

[Bill White]

:confused: Seems that somewhere in the deep, dark past I remember hearing that files could be soaked in an acid that would re-etch the teeth thereby sharpening them. Have I resorted to chronic brain cramps, or can this be done?
What was the acid? Phosphoric?
Bill

[David Cefai]

Use Hydrochloric Acid or Sulphuric Acid for this. You want an aggressive acid.

Sources: Sulphuric Acid is Battery Acid. Hydrochloric Acid is sold for descaling toilets.

You will need to experiment with the strength. I'd guess 1/4 diluted strong acid. You need a strength which will attack metal gently, evolving gas (hydrogen so avoid naked flames just in case)

WARNING: for Sulphuric acid, add acid to water, not vice versa. It heats up and can boil. Gloves & Goggles are essential unless you're an experienced elderly chemist (In my time we didn't use safety equipment in labs :))

This works because there will be a weak battery effect between the crevices and the tips of the teeth. Consequently more metal will be dissolved from the crevices than from the tips.

Make sure that the file is grease and debris free - possibly rinse it in a solvent.

Don't expect a fully rejuvenated file but it does work.

[Erik France]

A baking soda solution will neutralise the sulphuric acid. Make sure you protect them from rust as they will be very prone to it after the acid bath.

[Paul Saffold]

Bob Rozaieski just posted on his blog about sharpening rasp. Take a look at his video. I have used citric acid for both rasp and files, he uses white vinegar. Both are safer than strong acids but require at least overnight soaking.


http://www.logancabinetshoppe.com/1/post/2010/12/quick-tip-7-sharpen-a-rasp.html

Good luck, Paul

[Roger Newby]

I have also had good results with citric acid. It is slower but much safer and you can discard the solution safely in the garden or compost.

[Rick Markham]

WARNING: for Sulphuric acid, add acid to water, not vice versa. It heats up and can boil. Gloves & Goggles are essential unless you're an experienced elderly chemist (In my time we didn't use safety equipment in labs :))


ALWAYS ADD ACID TO WATER... this includes all strong acids, HCl too... If you add water to acid you are risking all of the acid molecules "jumping" on the singular water molecule and tearing it apart into it's component hydrogen and oxygen atoms... chances are "heating up an boiling" are probably the least of your worries, an exploding container of strong acid is more likely!

Be exceptionally careful using acids, if you get a severe acid burn, it will decalcify your body's buffering system, leading to DEATH. It doesn't take much, a spill on your leg is enough for you to spend days in the hospital with them telling you that there is nothing they can do for you. It would be a very horrible way to go.

Please be very careful, take all proper precautions, don't breath the fumes, you will be exceptionally sorry!

HCl is available as Muriatic acid (sold at pool supply stores, I am not sure what the concentration is, I highly doubt that it is 12 Molar) H2SO4 (sulfuric acid) is some nasty stuff, it is a strong acid with a weak acid counterpart, so it might be more difficult to neutralize than HCl, A gentleman here (who knows his stuff) told me after neutralizing HCl with a base (baking soda etc.) he has always "burned off" the remnants with a torch. I haven't tried it yet, but have several zinc coated bolts that will get an acid bath soon, so I will eventually.

I have spent many years in chemistry labs handling strong acids, do yourself the biggest favor you can and spend some time researching proper handling techniques.

Most lime scaling products are phosphoric acid ;) at least all of the ones I have ever seen.

[Dave Cav]

I have used full strength battery acid on files and it worked fine. You have to make sure they are clean, though. Scrub them thoroughly to get any oil or grease off.

There used to be a product called "chemsharp" available for "chemical sharpening" of just about anything you could soak in it. I bought a quart years ago and still have most of it. It worked fine on files and I'm sure it's just some sort of acid. I'm also sure it was taken off the market due to safety concerns.