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 Post subject: Mystery issue with Koishi
PostPosted: Tue Dec 13, 2016 5:13 pm 
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Joined: Thu Apr 19, 2012 1:18 pm
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Location: Madison Wisconsin
I had a customer contact me recently and said he had used his new Koishi a bit and the edge rolled on him to the point where it was completely dull. This didn't make sense to me since that knife steel is AS and it usually doesn't roll, it chips. So I offered to sharpen it for him and asked if he would mind if I took it home for a spin after I was done with it (I never use people's knives without asking). He's a nice guy and invited me to have at it. When I got the knife there was no edge on the entire blade. I could slide my fingers down the edge and nothing. When I looked at the edge there was 0 chipping. Very strange.

I sharpened it today when I got home from work and sharpened it. The steel felt hard and I got it screaming sharp. I'm going to test it out on some food and see if I can figure it out.

To be continued....



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Mark Richmond
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 Post subject: Re: Mystery issue with Koishi
PostPosted: Tue Dec 13, 2016 6:24 pm 

Joined: Sat Mar 01, 2014 1:15 am
Posts: 3040
Location: Raleigh, NC
What kind of cutting board does he use?


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 Post subject: Re: Mystery issue with Koishi
PostPosted: Tue Dec 13, 2016 9:04 pm 

Joined: Thu May 24, 2012 12:20 am
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I am waiting with baited breath...


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 Post subject: Re: Mystery issue with Koishi
PostPosted: Tue Dec 13, 2016 10:19 pm 
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I'm assuming it's a user error...or misuse. If you got it screaming sharp it ain't rolling...I would say.



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 Post subject: Re: Mystery issue with Koishi
PostPosted: Wed Dec 14, 2016 8:01 am 
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Joined: Mon May 28, 2012 6:29 pm
Posts: 1700
ANY steel can roll its edge regardless of hardness.

If the knife edge contacts something that is harder than the steel itself and the forces are being applied directly to the edge apex you are more likely to experience rolling or flattening of the edge.

Edge chipping is almost always the result of lateral side loading of the cutting edge or forceful chopping into a solid object. Side to side blade movement to separate food seems to be the biggest cause of such damage followed by frozen food and chopping into bone.

Hey Mark,

Did you happen to note the edge angle or overal bevel geometry before sharpening?


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 Post subject: Re: Mystery issue with Koishi
PostPosted: Wed Dec 14, 2016 8:23 am 
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And yes, that's what I was meaning to imply...that it's probably due to using it improperly. Not questioning your knowledge on the subject matter Jason!!!

On any hard knife I've had, chipping seems to be much more of an issue versus rolling. I've had troubles sharpening soft steels because of rolling however. I might think of this type of thing more as blunting, than rolling...due to using it on something harder than it.

But whatever, misuse vs poor quality control.



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 Post subject: Re: Mystery issue with Koishi
PostPosted: Wed Dec 14, 2016 8:38 am 
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My comments were for the masses and not directed at anyone :)


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 Post subject: Re: Mystery issue with Koishi
PostPosted: Wed Dec 14, 2016 8:55 am 
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Hmph. I can go with that... :)



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 Post subject: Re: Mystery issue with Koishi
PostPosted: Wed Dec 14, 2016 9:37 am 

Joined: Fri Sep 12, 2014 10:35 am
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Location: Annapolis, MD
Jason B. wrote: ANY steel can roll its edge regardless of hardness.

Yes, but the point at which steel breaks relates to its yield strength which, in turn relates to its elasticity which, in turn, relates (indirectly) to its hardness. When stressed within its elastic region steel can be bent and will recover. When stressed near the yield point, steel can bend but not recover fully. (When a metal brake bends sheet material "spring-back" is an issue for this reason.) When stressed beyond the yield point steel breaks.

So, the nature of this particular knife is going to be related to the makeup and heat treatment of the steel used to make it. Naturally, the specific technique employed by the user of the knife will effect the way in which the knife wears as well.



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 Post subject: Re: Mystery issue with Koishi
PostPosted: Wed Dec 14, 2016 10:03 am 
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You see Jason, I told you. You were wrong and I was right. :D

Like always... :D

jk.



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