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Testing for stress cracks?

Barrett X. Houston

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I've just started working with leaf spring, and while I love the stuff, I'm terrified of stress cracks. I'm afraid that while I'm using the knife the damn thing with fall apart on me :).


Once I'm done hardening and tempering, is there anyway to test for stress cracks? I think I remember hearing somewhere is that a good way is just to wack the back of the blade on something.

Edited by Barrett X. Houston

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Etching the blade will make cracks more visible, it will also allow you to differentiate between hardened and unhardened areas. I like to etch the springs before I use them and save myself some unpleasantness. I prefer to start with a sound piece of steel, that way if any cracks show up at the end, I know it was a problem with the heat treat. I had a large chopper that cracked halfway to the back during heat treat. I took it with me everytime I went camping for an entire year and abused the heck out of it. That blade cut a lot of firewood before it finally failed.



“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

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I agree etch with ARCHERS ECHANT ( the stuff they use for circuit boards try Tandy's store or good electrical outlets ) bit i Quench in oil anyway then de stress in the cooling forge till to hot to touch then Quench again


cheers tell

Terence.........(today started off perfect now --- watch sombody come and stuff it up ]


if it aint broke dont fix it

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I read on a forum (don't remember which one!) that Bill Moran would, after HT'ng and tempering, whack the spine of the blade on the horn of his anvil. If true, I think that process would serve several functions. The first, the blade fails or breaks. Second, the 'sound' of a good blade may differ from a blade containing a stress crack. Third, if in doubt, test some more or toss the blade. I think that technique was developed because it was quick and born of practical experience, i.e., if a crack is revealed, then the smith has minimized the work effort, and the cost, of finishing an unknown bad blade that he will warrant to his customer.

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I normaly go by the sound of the blade, and flex the blade pretty hard. Basicly treat the blade just a bit rougher than it will see in hard use, if it survives the test then you can be confident it won't let you (or a customer) down.



Ben Potter Bladesmith



It's not that I would trade my lot

Or any other man's,

Nor that I will be ashamed

Of my work torn hands-


For I have chosen the path I tread

Knowing it would be steep,

And I will take the joys thereof

And the consequences reap.

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I wish I could remember who to credit, but if you suspect a very small crack that needs tracking down, try kerosene. Do a quick belt or wire brush clean up of the surface and wet with the kerosene. Wipe dry and you can use an air nozzle across the surface to see the kerosene lifting out of tiny cracks that weren't visible. You can mix in magnification and angled lighting as needed.


Good luck with the heat treating, Craig

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I haven't tried either method but have come across two methods for non-destructive testing.

First is dip the piece in some light oil (kerosene will work or similar). Dry the piece off but don't use solvent. Rub chalk over the piece and warm the piece gently. If any oil has stayed in a crack on the surface, when warmed it will expand and flow out of the crack and be visible as it dampens the chalk.

The other involves magnets and iron filings but I don't remember enough details to describe the procedure. It is suppose to be able to find internal flaws.



Having watched government for some time, it has become obvious that our government is no longer for the people. If the current trend continues, it won't be long untill armed rebellion is required.

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Have seen Sensei Fogg hold a blade (sword ) lightly and tap it with a piece of metal. If it rings clear and true - no cracks. If it goes 'ckink' - then a crack somewhere. I don't know what size crack this is valid for ( large or micro ).


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if your forging the steel alot... stretching it out and shaping it.... if you watch it ...sometimes you can see if it has cracks.....


had that happen with o1 ... ... figured it out that after i forged a blade...that i'd hot cut off the forging and the stand the rod up in the corner... .. the ground being cold/frozen up here would cool the o1 too quick n crack it... .. so next time i'd go to for that bar, i could see cracks in the blade as i was making it... ( now i put that o1 to cool, wrapped up in kaowool.. )

- problem solved


if you want to see cracks... they usually show up in the polish




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