Apex angles vs. deburring'?

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azn_knives_4l

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Hi, y'all. I've been sharpening a bunch this last week for no reason other than I wanted to and hit everything from carbon Moras to Kiwis to Spydercos to paper thin Japanese kitchen knives. I noticed that some knives just... wouldn't de-burr? You'd expect it on the Kiwis and you'd be correct but more surprisingly I also encountered on my Kochi that barely has bevels.

Edge-trailing/edge-leading really didn't make much difference until I substantially increased the apex angle at which point even the Kiwis sharpened easily. My issue was the production of new foil, even edge-leading, at the limits of my motor skills. I'm thinking this is a variation on the 'too thin' or 'too low' concepts as they relate to edge stability and hoping to get your thoughts before experimenting more.

Thanks!
 
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Not being able to get deburred is characteristic of fatigued steel, or a sharpening angle that's much lower than the steel does take or hold. Or both...
With fatigued steel a lot of factory buffing is supposedly the culprit. Or overly steeled vintage carbons, although uncooled grinding may explain it as well.
Steel composition: have soft stainless in mind. Krupp's 4116 requires a minimal sharpening angle to offer some edge stability. For marketing reasons makers go far below.
 
Benuser said:
Not being able to get deburred is characteristic of fatigued steel, or a sharpening angle that's much lower than the steel does take or hold. Or both...
With fatigued steel a lot of factory buffing is supposedly the culprit. Or overly steeled vintage carbons, although uncooled grinding may explain it as well.
Steel composition: have soft stainless in mind. Krupp's 4116 requires a minimal sharpening angle to offer some edge stability. For marketing reasons makers go far below.
Click to expand...
I thought this, too, about 'fatigued steel' so flattened and sharpened all low pressure edge-leading, despite slow af, and it made no difference to either Kiwi or Kochi.
 
Benuser said:
Not being able to get deburred is characteristic of fatigued steel, or a sharpening angle that's much lower than the steel does take or hold. Or both...
With fatigued steel a lot of factory buffing is supposedly the culprit. Or overly steeled vintage carbons, although uncooled grinding may explain it as well.
Steel composition: have soft stainless in mind. Krupp's 4116 requires a minimal sharpening angle to offer some edge stability. For marketing reasons makers go far below.
Click to expand...
Also, thanks for the confirm on apex angles. I don't use/sharpen the Kochi very often so it was a bit of a shocker. I'd been doing the extremely high micro-bevel just for edge stability but tried something new to test/experiment and ran into this phenomenon. 'Crumbling' is how I've described excessively thin edges relative to stability in the past but I'm quite more knowledgeable now than I was then.
 
Some factory edges are only meant as a service to the end-user. Certainly for real-life use involving board contact. With a few strokes you get them within the margins of what's reasonable. Up to you whether you do it in the form of a micro-bevel or not.
As for the cases of fatigued steel, they really need a generous removal of the entire edge. A coarse stone and some thinning to compensate.
 
Benuser said:
Some factory edges are only meant as a service to the end-user. Certainly not meant for real-life use involving board contact. With a few strokes you get them within the margins of what's reasonable. Up to you whether you do it in the form of a micr-bevel or not.
As for the cases of fatigued steel, they really need a generous removal of the entire edge. A coarse stone and some thinning to compensate.
Click to expand...
Yeh. I'm in the 'show me' camp as far as edge fatigue, lol. Stamp famously made some *big* claims but never substantiated.
 
azn_knives_4l said:
Yeh. I'm in the 'show me' camp as far as edge fatigue, lol. Stamp famously made some *big* claims but never substantiated.
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Not that hard to prove: remove all of the edge with a coarse stone, and rebuild a similar geometry.
Have seen factory edges made on a very coarse medium, directly followed by a lot of buffing. Looking great, but that's all. Crumbling after the board contact.
 
Benuser said:
Not that hard to prove: remove all of the edge with a coarse stone, and rebuild a similar geometry.
Have seen factory edges made on a very coarse medium, directly followed by a lot of buffing. Looking great, but that's all. Crumbling after the board contact.
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Right. I've found this doesn't make a meaningful difference vs. traditional hand-sharpened edges.
 
So what Ben says below is basically the answer (ime):
Benuser said:
Not being able to get deburred is characteristic of fatigued steel, or a sharpening angle that's much lower than the steel does take or hold. Or both...
Click to expand...


However in some situations you're on a bit of a hiding to nothing whatever way you spin it:
azn_knives_4l said:
it made no difference to either Kiwi
Click to expand...

Kiwis are made from significantly softer steel than any other commercially available knife I've sharpened, and they're also very thin. You can form burrs, or what feel like burrs, on Kiwi knives very easily. But they don't behave like burrs on harder steels, and are extremely difficult to get rid of, cos you're just kinda shoving soft steel from side to side. I tend to sharpen them at very low pressure throughout to try to avoid this as much as possible.

I thought your vid sharpening a Kiwi one-handed on sandpaper was dead impressive btw! You have absolutely nothing to worry about in terms of technique, I wouldn't change it in any way. That could be used as an instructional video demonstrating how to do the end stages of sharpening and deburring well.

(I dunno about Kochi, but it's possible the HT might have been a bit screwy?)
 
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cotedupy said:
So what Ben says below is basically the answer (ime):



However in some situations you're on a bit of a hiding to nothing whatever way you spin it...



Kiwis are made from significantly softer steel than any other commercially available knife I've sharpened, and they're also very thin. You can form burrs, or what feel burrs, on Kiwi knives very easily. But they don't behave like burrs on harder steels, and are extremely difficult to get rid of, cos you're just kinda shoving soft steel from side to side. I tend to sharpen them at very low pressure throughout to avoid this as much as possible.

I thought your vid sharpening a Kiwi one-handed on sandpaper was dead impressive btw! You have absolutely nothing to worry about in terms of technique, I wouldn't change it in any way. That could be used as an instructional video demonstrating how to do the end stages of sharpening and deburring well.

(I dunno about Kochi, but it's possible the HT might have been a bit screwy?)
Click to expand...
I had to Google that one, lol, and I think you're right. Whether it's due to fatigue, extreme geometry, shoddy HT, retained austenite, etc. is all moot when we have the solution. I remembered reading something on Science of Sharp about edge-leading preventing burrs to be generally true but not 100% and I know this from experience. Unfortunately, the author didn't go into much detail on the mechanisms for whatever reason and I was surprised to find the absolute apex angle itself to be important and not just as it relates to the sharpening angle (i.e. micro-bevel/high angle passes). I also think you're spot-on regarding the flimsy character and it also fits nicely with the hard/soft material narrative since any steel becomes foil at the right dimensions.

Thanks for the kind words on the Kiwi demo 😀 I'll be back with some Kochi paper towel cutting soon. I don't use it much because carbon steel and I just don't mix in the kitchen but pulled it out to evaluate your statements to the importance of geometry in the 'drop'. Ofc, you are correct 😉
 
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