help with 'file' test for hardness

[Scott Roush]

I was wondering about using small triangular files for testing for hardness during heat treating... from reading, it sounds like some folks like to use new, sharp files and some prefer old, dull ones.  This morning, I laid out some different steels to try to get a feel for what to look for when I start heat treating my blades.  I tried it on some brand new Nicholson mill files and my little, dull file pretty much glanced off, but if I apply a little more pressure I can make a little cut.. same with some Dexter high carbon filet knives and some other stuff. So... how much pressure do you use? And I suppose if I'm doing it on the spine of a commercial knife... then that spine may have been soft drawn... or edge quenched I guess.

Anyway... how do you folks do it?  I'm also looking for some 1/4" brass to do some brass tests..

[Lin Rhea]

mossanimal,
             I use a file, period. If I have a new one, I use it, if I have an old one, I can use it too, but know that it will cut like an older/duller file. Your just comparing. You know how a knew sharp file cuts steel that's not hardened. Steel like angle iron, which is usually mild steel or 1018 will be easy to cut with clear, deep, and well defined filemarks.

  A piece of high carbon steel that has been hardened will be more difficult to cut since the steel's hardness is approaching the hardness of, or even as hard as the file. A sharper file will naturally cut easier than a dull file, but when the blade is successfully hardened, you will be able to feel the difference. It should skate, not removing any material, and make a whining sound. One stroke should tell you. Dont get too rough trying to force it to cut. You can break the blade at this point. All your wanting is to know it got hard. If you doubt your file, find a piece of mild steel and try to cut it with the file, then try your hardened blade. By the way, I just check the cutting edge, unless for some reason I want to compare the edge to the spine.

    I want my edge hardened and the rest can be some degrees softer, especially where I know I will have to drill or square with a file. Lin

[Scott Roush]

Thanks Lin... I just found out why I was having a hard time... a lot of the steel I was comparing (other than those Nic files) were all soft anyway. I was mostly comparing apples to apples.  But I'm getting out some of my other hunting knives. I will get it...