Chipping?

ra1p3 said:
Two Japanese kitchen knives sharpened with the same method to the same angle.

This one is my old one, sharpened many many times during the years.
https://imgur.com/3z9AXI2

This is a new knife resharpened for the first time.
https://imgur.com/7fPTHSH

What is happening here? Why is the new one chipping like that?
Click to expand...
You haven't given nearly enough info to make anything other than a guess.

Did you sharpen both knives?
Freehand or some sort of guided system or other?
What sort of abrasive was used to sharpen them?
Are they the same model/brand knife?
Do they have the same blade steel?

It's possible that the new knife was sharpened at the factory on a belt or similar and the edge was overheated. If this was the case, then you can eventually remove enough material to get to good steel underneath but it may take a few sharpening sessions. If the new knife is some hard, high carbide volume powder steel, then it may turn out better using a lighter touch and trying to avoid creating a large burr as you create the apex. This is all blind speculation though, it could be anything.

Edit: also this must be a record for the oldest account making their first post. Account nearly 12 years old, well done.
 
chalby said:
You haven't given nearly enough info to make anything other than a guess.

Did you sharpen both knives?
Freehand or some sort of guided system or other?
What sort of abrasive was used to sharpen them?
Are they the same model/brand knife?
Do they have the same blade steel?

It's possible that the new knife was sharpened at the factory on a belt or similar and the edge was overheated. If this was the case, then you can eventually remove enough material to get to good steel underneath but it may take a few sharpening sessions. If the new knife is some hard, high carbide volume powder steel, then it may turn out better using a lighter touch and trying to avoid creating a large burr as you create the apex. This is all blind speculation though, it could be anything.

Edit: also this must be a record for the oldest account making their first post. Account nearly 12 years old, well done.
Click to expand...

> Did you sharpen both knives?
yes

> Freehand or some sort of guided system or other?
freehand

> What sort of abrasive was used to sharpen them?
ceramic

> Are they the same model/brand knife?
nope. different brand and model: old: watanabe nakiri, new: Akifusa hakata

> Do they have the same blade steel?
new one is: Aogamisuper. Older is: Yasuki white steel #2

> also this must be a record for the oldest account making their first post. Account nearly 12 years old, well done.
thanks, it took some time to gather courage
 
Interesting post. Did you reach the apex in the top knife? Looks like you stopped just short.

The magnification seems different -- higher in the lower photo.

The scratch patterns seem different. There are cross-scratches in the lower photo, but maybe there's a magnification difference.

The "chipping" looks more like a torn wire edge, but I don't see a burr.

My Aogami Super Blue chef's knife is run hard -- 64 Rc -- and it will chip. My white steel, run softer, never chips.
 
If nothing else those knives and steel names sound very exotic.
Did you use Naoguma or Shirusaki technique when sharpening them?
 
Try using lower pressure with the (presumably) harder steel. Also the grit scratches make it appear you're using too fine a stone to clean up that edge. in a reasonable amount of time.
 
UncleBoots said:
Try using lower pressure with the (presumably) harder steel. Also the grit scratches make it appear you're using too fine a stone to clean up that edge. in a reasonable amount of time.
Click to expand...
I am not that of an expert and do not know if the other one is harder. Can you elaborate on your note about the grit scratches, I do not understand it. Thanks!
 
Twindog said:
My Aogami Super Blue chef's knife is run hard -- 64 Rc -- and it will chip. My white steel, run softer, never chips.
Click to expand...
Aha! OK. I do not know the hardness of my white steel but the AogamiSuper is indeed around that. So I need to do larger sharpening angle then for that?
 
ra1p3 said:
I am not that of an expert and do not know if the other one is harder. Can you elaborate on your note about the grit scratches, I do not understand it. Thanks!
Click to expand...
I observed that the scratches near the edge seem quite tiny compared to the damage in the edge, as though a stone fine enough to make such scratches would be slow enough to remove metal, that it would not be a good choice to repair the edge.

What magnification are you using? I have seen damage like that at high magnification only from tearing off a burr. Some people like to do that with hard felt or cork or wood, but with a heavy burr, you can wind up with something like this.

If you are using low magnification, say 60 or below, it starts to seem as though it would be something else. The only other phenomenon I've seen produce that pattern of damage at such a scale is using way too much pressure when sharpening a knife with hard steel.
 
Normally in a case like this I would suspect heat damage done by the factory (aggressive use of belt sander), but this sounds like a high-end Japanese knife, so that seems unlikely. But if that is the case, the answer is to keep grinding until you hit steel that hasn't been detempered.
 
If you have used the new knife and then sharpened it, it may be that you didn't quite remove the wear/damage from use. In other words maybe you didn't quite apex the edge along the whole length. It's hard to say. I would go back to a reasonably coarse stone and sharpen it again trying to use reasonably light pressure and see what it looks like after another sharpening.
 
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