Having Too Hard a Time Checking Hardness!

G

Geoffrey Raiser

Joined
Sep 24, 2003
Messages
118
Have I been silly? I’ve been assuming that if I can fairly easily remove metal from a knife edge with my miniature Nicholson flat file (from set #42030) that the steel is too soft.

However, last night I used this method to check the hardness of an old Chicago Cutlery cleaver that holds its edge very well, and I found that the file cut it fairly easily too!

Using a file to check hardness has been often mentioned in this forum, but now I’m wondering if I’m doing it wrong. Maybe the miniature Nicholson file I’m using is super hard and has extra sharp teeth. I’ve used this file quite a lot on mild steel and it still cuts it like butter. What is the typical hardness of a decent file?

I’ve about convinced myself that I am doing this hardness check wrong. What is the proper way to do this, and what kind of file should I be using?

Thanks in advance for your generous help!!!!

Geoffrey :)
 
Geoffrey Raiser said:
Using a file to check hardness has been often mentioned in this forum, ...
Click to expand...

Geoffrey,

You won't really be able to test the hardness of a blade using a standard file; as a file will be several points higher in hardness to a tempered blade(<60).
What is talked about on the forums is finding the hardened area of the khuk (sweet spot).
You should be able to tell the difference between it and the softer area around it. Start near the cho with just enough pressure to feel the file bite, maintain that pressure while moving the file along the edge; when you hit the sweet spot your file should seem to skip as it will not bite the hardened area as easily as the soft with the same pressure.

That said, there are/were files designed to test hardness (though not as accurately as other methods); they usually came as a kit with each file marked as to what hardness it was tempered to. I don't know if they are even made anymore.

Regards,
Greg
 
The miniature nicholson files I have used are hardened to 64. Most files are at least 62.

Your typical khukuri is probably 55-58.
 
Thanks Greg and Dan. Makes sense... I'll give up trying to quantify hardness with the file method. Does the hot soapy vinegar etch give a good indication? I have some khukuries that show a very clear, highly visible hardened zone, while others are much more subtle and hard-to-see. Would you expect that the ones with the more prominent contrast have harder edges? Or is this, too, simply a more a qualitative indication of where the sweet spot is?

Thanks again!!!

Geoffrey
 
Geoffrey,

I believe it is simply a more a qualitative indication of where the sweet spot is.
There are lots of things that could affect the different appearances of the etch besides the hardness; surface condition of the steel, temperature/concentration/age of the etching medium, duration of the etch, variance in the steel composition, etc. would all have some effect.

Shy of using a hardness tester, you might try doing a " brass rod " test to check for working hardness.

Then again; there are those that will say: "just use it and see if it works".

Regards,
Greg

Edit: Thanks for posting that link n2s!
 
My wife was polite enough to inform me - while reading this thread over my shoulder - that:

"Only on the HI Forum would you have a thread with 'Checking Hardness' in the title and no naughty pictures and nobody getting in trouble!"

:eek:



:footinmou
 
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