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How to sharpen a file?

How to sharpen a file?

Once a file becomes worn, it is useless and should therefore either be discarded or sharpened.


You can tell if a file is worn out when it is no longer doing its job effectively, for example skating over the top of a workpiece instead of removing any material.

Guide to Sharpening a File by Etching

You can attempt to resharpen any file quickly and simply by etching. This process involves the use of acid, which eats away at the surface of the metal, making the teeth narrower and causing their tips to form more of a point.

Step 1 - Create an Acid Bath and an Alkali Bath

In order to etch your file, you will need to create a 10% solution of sulphuric acid in water in a container large enough to allow the body of the file to be submerged.


You will need to fill another container of the same size with a saturated solution of bicarbonate of soda, for rinsing.

You will know that you have created a saturated solution when you can’t make any more bicarbonate of soda dissolve in the liquid. This will result in the bicarb granules sitting on the bottom of your container.


Bicarbonate of soda is alkaline. Rinsing your file in a solution containing bicarb after it has been etched will neutralise the acid and prevent it from continuing to eat away at the file.

Step 2 - Etch File

Remove your file’s handle if you can, then submerge the body of the file in the sulphuric acid solution.

Step 3 - Put Your Feet Up

Leave it for an hour. Time to get those feet up!

Step 4 - Rinse File

Once the file has been sat in the acid bath for an hour, rinse it thoroughly by swilling it in the alkali bath.


Make sure your file is properly dry afterwards, to prevent rusting.


Your file should now be sharp enough to use once again.

Guide to Sharpening a File by Etching

This process is not particularly well suited to the home DIYer, as it involves annealing the file and then grinding off all of its teeth before recutting them again.


From there, the file goes back through the heat treating process, before being reborn as a brand new file.


For more information on the tooth cutting and heat-treating processes, as well as an explanation of annealing, see: How are files made?

Should I Re-Sharpen my File?

The best way to make this decision is to weigh up the cost involved. If buying in the materials that you need to etch your file sharp is cheaper than buying a new file then you might want to consider giving it a go.


If you do choose to sharpen your file, it’s worth bearing in mind that it will not be as sharp as a brand new file.


Of course, if you’re an amateur blacksmith then you may have the facilities to re-cut your file yourself. If you don’t, though, the cost of re-cutting the file is likely to be a lot more than buying a new one.

Recycling Files

If you decide that it’s time for your file to go to the great tool drawer in the sky, you may want to consider recycling it. Many metalworkers grind old files and rasps into knives by shaping and sharpening the edges with a grinding wheel.

Wonkee Donkee Tools