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Edge thickness before quench.


Oberu

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Heya fellows.  I’ve been commissioned to make a chef knife for a friend. It’s a damascus blade and I’ve put a photo in for reference. The thickness at the spine is ~ 0.135” and my question is how thin would you take the edge before quenching? I’ve got the main bevels in and the edge is ~ 0.065”.  I’ll be using my forge and warmed canola. I know this isn’t the ideal method but it’s what I have access to.  Thanks 

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I wouldn't go any thinner.  Cracking isn't the problem in an oil quench, it's the dreaded potato-chip warp of the thin edge.  Normalize the heck out of it and keep it perfectly vertical (edge to spine or point to tang)  in the quench, and do not agitate.  Single wobbles can be fixed in the tempering cycles, but a full-on bacon strip edge is not fixable.  By me, anyway.  Joshua States has some cool videos about how he clamps a blade immediately out of the quench while it's still a bit flexible to prevent that sort of warp.

 

Good luck!

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I was about to quote Alan's comment about the un-fixability of bacon edges, but then he added his caveat.  I make pretty thin blades, typically about 0.090"-0.070" at the spine, and I typically go to about 0.050" at the edge.  But thicker is better for preventing warping, you just have more post HT grinding to do.  

I've been forging and grinding thinner and thinner on my last few blades, partly to see where my cut-off point is and my last one was 0.0.030 at the edge before quench and that looked like a piece of bacon.  It took 5 tempering cycles to fix it.  I can go into more details of my process if you want. 

Good luck, can't wait to see pics.

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RIP Bear....be free!

 

as always

peace and love

billyO

 

 

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24 minutes ago, Brian Myers said:

a great rule of thumb is to not grind the edge any thinner than a dime.

Now that you mention it, I've heard that before (getting out my calipers and reaching for a dime...0.050")

Maybe that's why I was stopping there before pushing the envelope.

Thanks for the reminder, Brian.

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RIP Bear....be free!

 

as always

peace and love

billyO

 

 

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Thanks fellows.  I've made quite a few knives over the years but never one with this sort of proportion.  The thin cross section gave me pause.  I appreciate all of the help and I'll implement it.  My gut told me to stop where I was and ask.. smart gut.  I've had some weird stuff happen when I work with cross sections in weird proportions.. like a really long triangular dirk.. sabered like crazy on me and I lost almost two inches off length and had to re-profile the whole thing.  Good on ya fellows!

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i think if you just quench the edge that can help keep a blade from warping but i havent done enough kitchen knives to really say. the ones i did make i quenched at the same thickness i would for other blades which is a little thinner than a dime and they came out fine. a few of them were japanese single bevel knives that can warp like nobodies business. 

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4 hours ago, steven smith said:

 

i think if you just quench the edge that can help keep a blade from warping

 

I’ve had that bacon too. I think it’s because martensite is a little longer than austenite so the only way the expansion could go was sideways. Correct me if I’m wrong. 

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"The way we win matters" (Ender Wiggins) Orson Scott Card

 

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typically if I'm worried I'll pull directly from the quench and clamp in steel or wood (depending on size).  Clamping immediately seems to stop a lot of the troubles.  There have been times.. like my sabering where this didn't work.  Wrinkles in the edge I can do something for.. the edge dropping towards the edge..done deal..  she gone

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I've snapped one too many blades by trying this method:(, so what I do is do a one hour temper immediately after the quench, then use subsequent tempering cycles to fix any severely warped or bacon-like edges. On blades that are straight out of the quench,  I normally do two 2-hour cycles anyway, and if the blade isn't warped too badly, the correction during the second cycle usually fixes any problems.

 

How did this one turn out? (or haven't you done it yet..)

Edited by billyO
RIP Bear....be free!

 

as always

peace and love

billyO

 

 

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On a blade with a thick wedge cross section like that dirk, a nosedive during the quench is inevitable.  I too have lost a couple of inches off the tip when making dirks. The only way to avoid that is to use a very shallow-hardening steel and quench in a superfast oil like Parks 50 or water/brine.  Even then, it makes me happy to see langsaxes in the Museum of Norway that have a distinct yataghan-looking curve from this effect. B)

 

This is all the sori effect the Japanese use to get the curve in katana.  The combination of sectional geometry, extremely shallow depth of hardening, and extremely fast quench results in the classic curve.  The blade goes in perfectly straight, immediately nosedives, then curves back up.  Somewhere around here there's a video of a guy quenching a katana in a glass tank so you can see the extreme contortions the blade goes through during the quench.

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1 hour ago, Alan Longmire said:

Somewhere around here there's a video of a guy quenching a katana in a glass tank so you can see the extreme contortions the blade goes through during the quench.

This is the one I show to people:

 

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I forge this style of dirk with a straight spine and a bit of belly to the edge. The belly straightens out in the quench, pulling the tip down to the centre line, and you can tidy up the profile without losing any length.

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Jake Cleland - Skye Knives

www.knifemaker.co.uk

"We can't solve problems by using the same kind of thinking we used when we created them."

"Everything should be made as simple as possible, but not simpler."

"Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe."

 

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57 minutes ago, jake cleland said:

I forge this style of dirk with a straight spine and a bit of belly to the edge. The belly straightens out in the quench, pulling the tip down to the centre line, and you can tidy up the profile without losing any length.

 

That's because you've done a lot of these and are VERY good at them! :lol:  Seriously though, that's a great tip!  

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27 minutes ago, Brian Myers said:

Is it just me or do I hear the dreaded "tink" right at the end?

I think that is something in the background, not happening in the tank.  

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