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Reading some reviews of knives I often read the words "edge stability", what is the real meaning of these terms?
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Definition of "Edge stabiliy"
- Thread starter jimhawkins
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We're working on that and someone may get back to you. 
For now, it refers to the ability of an edge to resist rolling, denting, and chipping within a given range of angles within a given range of widths at shoulder within a given range of applied forces (lateral, longitudinal, torsional).
Sound muddy and like it could mean anything and nothing? You betcha!
Where I try to start is to compare two knives with the same steel and a different hardness. I have a Benchmade Switchback pocketknife and its longer blade is made of CPM-S30V. At RC58, it took a 24 included degree edge (12 degrees per side) and handled my cutting of boxes and plastic. At 10 degrees per side, the edge rolled and wouldn't stay sharp. Worse, it wouldn't even let me apply a 30 degree microbevel without rolling all over the place either. Knifemaker Phil Wilson redid the heat-treatment on my pocketknife so that the steel was at RC61 for hardness and now it easily takes a 24 degree microbevel (12 per side), but I ground the edge so thin that it won't do stuff most people do with S30V.
For now, it refers to the ability of an edge to resist rolling, denting, and chipping within a given range of angles within a given range of widths at shoulder within a given range of applied forces (lateral, longitudinal, torsional).
Sound muddy and like it could mean anything and nothing? You betcha!
Where I try to start is to compare two knives with the same steel and a different hardness. I have a Benchmade Switchback pocketknife and its longer blade is made of CPM-S30V. At RC58, it took a 24 included degree edge (12 degrees per side) and handled my cutting of boxes and plastic. At 10 degrees per side, the edge rolled and wouldn't stay sharp. Worse, it wouldn't even let me apply a 30 degree microbevel without rolling all over the place either. Knifemaker Phil Wilson redid the heat-treatment on my pocketknife so that the steel was at RC61 for hardness and now it easily takes a 24 degree microbevel (12 per side), but I ground the edge so thin that it won't do stuff most people do with S30V.
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I thank you, bye
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Okay, that example was muddy, too.
For me, it suggested that S30V at a hardness of RC58 needs to be thicker than S30V at a hardness of RC61 to handle a low edge angle without rolling. While the RC numbers probably differ, that generality is probably true about most steels.
We can get into the geeky stuff about carbide fraction volume and such, but my experience has been that unless you're going for edges so thin that you can only see the blade on a full moon at a crossroads, it only explains why some steels sharpen quicker than others and why some steels roll when ground too thin for your uses and others roll and crack.
My examples of what I've seen involving carbide volume: Hitachi Blue Super steel; as heat-treated by the Takeda Hamono shop; will take an edge that's five degrees per side (Gunmike1 has sharpened a similar knife to 4 degrees per side). I don't think that can be done with VG-10 or CPM-S90V. But then, if you don't use an closed-cell wooden cutting board and lots of care, that 10-included degree edge will microchip, well, just the way anyone might expect a very thin, barely tempered piece of steel to chip when being repeatedly slammed through food into hardwood (will slice forever, though). On my Kershaws, I kinda sorta overground the edges my External Toggle and SG-2 Blur (they're okay now, though) for their given tasks. They have deep hollow grinds which may regrinding easy and I like my edges waifer-thin. So I screwed up and made the ET too thin to twist while cutting plastic and the Blur too thin to cut unsupported wire ties (but just right for cutting chores done by people who aren't cuckoo in la cabesa). When those edges rolled, the 13C26 of the ET was just rolled and the SG-2 of the Blur was cracked. Resharpened 'em at slightly thicker angle and avoid wire ties with them and problema nada.
So all of that above explains some "edge stability" stuff that won't and shouldn't matter to most anyone.
Where it might matter is if you're absolutely obsessed with having edges sharpened to 10 degrees per side and staying just above shaving sharp after the initial sharper edge wears away. Should also matter with woodworking tools.
That's my take on it, but the smarter folks should chime in soon.
For me, it suggested that S30V at a hardness of RC58 needs to be thicker than S30V at a hardness of RC61 to handle a low edge angle without rolling. While the RC numbers probably differ, that generality is probably true about most steels.
We can get into the geeky stuff about carbide fraction volume and such, but my experience has been that unless you're going for edges so thin that you can only see the blade on a full moon at a crossroads, it only explains why some steels sharpen quicker than others and why some steels roll when ground too thin for your uses and others roll and crack.
My examples of what I've seen involving carbide volume: Hitachi Blue Super steel; as heat-treated by the Takeda Hamono shop; will take an edge that's five degrees per side (Gunmike1 has sharpened a similar knife to 4 degrees per side). I don't think that can be done with VG-10 or CPM-S90V. But then, if you don't use an closed-cell wooden cutting board and lots of care, that 10-included degree edge will microchip, well, just the way anyone might expect a very thin, barely tempered piece of steel to chip when being repeatedly slammed through food into hardwood (will slice forever, though). On my Kershaws, I kinda sorta overground the edges my External Toggle and SG-2 Blur (they're okay now, though) for their given tasks. They have deep hollow grinds which may regrinding easy and I like my edges waifer-thin. So I screwed up and made the ET too thin to twist while cutting plastic and the Blur too thin to cut unsupported wire ties (but just right for cutting chores done by people who aren't cuckoo in la cabesa). When those edges rolled, the 13C26 of the ET was just rolled and the SG-2 of the Blur was cracked. Resharpened 'em at slightly thicker angle and avoid wire ties with them and problema nada.
So all of that above explains some "edge stability" stuff that won't and shouldn't matter to most anyone.
Where it might matter is if you're absolutely obsessed with having edges sharpened to 10 degrees per side and staying just above shaving sharp after the initial sharper edge wears away. Should also matter with woodworking tools.
That's my take on it, but the smarter folks should chime in soon.
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As far as I have been able to determine, knife forums are the only place you'll ever even hear the term used. It is not a recognized material property. I've asked in the past here for information on how "edge stability" is actually measured, tested for, or otherwise determined, and received no answers.
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Oh sure, say what I said, but in a few sentences and without long, drawn-out anecdotes involving super-cool pocketknives.:grumpy:
Jim,
Taken to simplest terms, edge stability just means staying sharp during use and abuse. We BladeForums fanatics will debate sharpening angles, bevel profiles, steels, and failure mechanisms, 'till the cows come home ... all part of the culture.
Welcome to our world,
Ray
Taken to simplest terms, edge stability just means staying sharp during use and abuse. We BladeForums fanatics will debate sharpening angles, bevel profiles, steels, and failure mechanisms, 'till the cows come home ... all part of the culture.
Welcome to our world,
Ray
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Sorry Thom, didn't mean to step on your toes. I think your descriptions are as good as I've seen.
What I recall is that it is tested by exerting a lateral force on the knife edge, but that is pretty much all the detail I've seen. The angle, thickness, and finish of the test edge is unknown, as is the force applied and how it is applied. I recall it was implied that the test is done on a razor type edge, so it is undoubtedly thin, fine, and polished. I presume the steel would be "rated" somehow after the force is applied by observing the edge and corresponding damage or chipping due to the lateral force.
It has been presented as Thom describes above, the ability of a fine edge to keep a fine edge, but how the correlation to that was made from the direct test results is unknown (and available only in a metallurgy book printed in german). I think the correlation assumes that all or most edge degradation is caused by lateral forces on the edge during cutting, which is also something that is not agreed on by all.
In my opinion it is a measure that is only applicable to razor or kitchen edges, but that is just my opinion based on guesses. I suspect for many kinds of everyday utility cutting chores, other steel characteristics (hardness, wear resistance) are more important in increasing performance.
Basically it is one more not very well defined term for knife performance, like edge retention and sharpness (assuming there still folks here who insist on calling slicing ability sharpness!). So again, welcome to our world!
What I recall is that it is tested by exerting a lateral force on the knife edge, but that is pretty much all the detail I've seen. The angle, thickness, and finish of the test edge is unknown, as is the force applied and how it is applied. I recall it was implied that the test is done on a razor type edge, so it is undoubtedly thin, fine, and polished. I presume the steel would be "rated" somehow after the force is applied by observing the edge and corresponding damage or chipping due to the lateral force.
It has been presented as Thom describes above, the ability of a fine edge to keep a fine edge, but how the correlation to that was made from the direct test results is unknown (and available only in a metallurgy book printed in german). I think the correlation assumes that all or most edge degradation is caused by lateral forces on the edge during cutting, which is also something that is not agreed on by all.
In my opinion it is a measure that is only applicable to razor or kitchen edges, but that is just my opinion based on guesses. I suspect for many kinds of everyday utility cutting chores, other steel characteristics (hardness, wear resistance) are more important in increasing performance.
Basically it is one more not very well defined term for knife performance, like edge retention and sharpness (assuming there still folks here who insist on calling slicing ability sharpness!). So again, welcome to our world!
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I believe "edge stability" consists of two things. Edge rolling or edge chipping (microchipping).
While wear resistance is a measure of an idealized cutting with no bending forces whatsoever. Edge stability is what really happens. Most cutting chores includes bending, lateral forces or hard spots (like sand) that will accelarate the edge destruction.
Edge rolling OR microchipping will happen to any knife if pushed hard enough. Fine grain steels and carbon steels will generally roll, and powder steels and tool steels will generally chip. Due to the high carbide density = decreased toughness.
I believe the impact of edge stability in normal use is much greater than the impact of wear resistance. Which leads me to not take for instance CATRA-tests very seriously, since they only test wear resistance (or actually re-grindability, but thats another topic).
While wear resistance is a measure of an idealized cutting with no bending forces whatsoever. Edge stability is what really happens. Most cutting chores includes bending, lateral forces or hard spots (like sand) that will accelarate the edge destruction.
Edge rolling OR microchipping will happen to any knife if pushed hard enough. Fine grain steels and carbon steels will generally roll, and powder steels and tool steels will generally chip. Due to the high carbide density = decreased toughness.
I believe the impact of edge stability in normal use is much greater than the impact of wear resistance. Which leads me to not take for instance CATRA-tests very seriously, since they only test wear resistance (or actually re-grindability, but thats another topic).