Apex Stability vs Edge Retention

[samuraistuart]

Can we talk about the difference between "apex stability" (AS) and "edge retention" (ER)? I think I can differentiate between the two, but would like to discuss this with you fellow sharpening knife knuts. Seems like there is a 3rd term associated with the other 2, but it escapes me at the moment. I'm backyard shade tree mechanic type....I really like learning new things/ideas/topics and not afraid to show my ignorance, as you can see from below:

Apex stability: The ability for the tip of the "triangle" formed by two intersecting planes to withstand chipping and/or rolling. Adhesive wear would play no role in "AS", but abrasive wear most definitely would.

Edge retention: Also the ability of the apex formed by the two intersecting planes to withstand chipping and/or rolling. Adhesive wear CAN play a role in degrading "ER", as well as abrasive wear. ???Most often refers to the overall working condition of the edge itself, not a specific location on the edge???

If a lateral load was placed upon an edge that was too great for it's strength, causing a chip to occur, then the AS suffered, at that spot, but ER overall (entire length of edge) may not have suffered, and is still serviceable. Someone may not notice the chip (AS failure), because the rest of the edge is still doing it's job, so even tho AS may not be as good as it could/should be, we would say the ER is OK?

2 blades identical in geometry, both having the best heat treat, 10V and 1095: I would expect 1095 to have better AS (generally speaking), but the 10V to have better overall ER.

That sound right to you? I REALLY appreciate any corrections, additions, and input. LOTS of very knowledgeable minds here.

 

[BluntCut MetalWorks]

Given everything the same: dimension; geometry; interaction forces (operator & techniques); tasks; etc...

So for given lengthy tasks (only end when edge failed - e.g. can't slice air slice paracord in one stroke) and fixed budget/allot energy.

Performance = finished highest number of tasks/repetitions
* it can break into buckets when optimize certain range rather than life time ^

Which directly based on

Edge Damage Resistant can be consider as a parent of Apex stability & Edge Retention. Where 'stability' is capability and 'Retention' is damage rate.

Damages: deformation (fractured, dent, rolled, ..) + wear (ruptured, binded, pulled, abraded, ..) + thermal(ok, ignore this one)

Given 2 awesome ht 10V vs 1095. 1095 has low carbide volume so fracture less than 10V. And other deformations more/less similar. Converse, 10V high cv provides more wear resistant than 1095. There is a vast gray space between these clear cut cases -

Functional wise: As you pointed out a chipped edge can continue cuttings, while same depth rolled+dent deformation would failed - no longer able to perform tasks. Ironically, many think/perceive chipped edge as failed. Perhaps, some element of truth because in fixing a chipped usually remove a tiny bit (10-15% my wag) more than a rolled edge. My ht edge aim for initial deformation in ripple mode, then lead to chip. I think, a rippled edge would performs better than chipped and way better than rolled.

btw to me - ruptured = cracked below steel surface. e.g. high pressure cut against sharp corner of ceramic object (such as edge of a ceramic plate). High cv and or low ductility steels are more susceptible to this type of damage.

Aha - I steer everything toward performance - sitting bias pretty

 

[samuraistuart]

Someone besides this guy ^. Apex stability vs edge retention. What are the differences.

 

[bodog]

I think they're really the same unless you're wanting to equate apex stability and apex strength. In that case apex strength would be a specific trait of a given steel with a given heat treatment at a specific geometry.

They're all just words meaning keeping an edge that'll cut. Different materials being cut in different manners dictate different traits of a finished blade but it's all about keeping the apex stable/ edge retained.

I do think people often confuse specific traits or small groups of traits with overall performance in a specific task. When you say knife x retains an edge in carboard but has low apex stability when carving wood, really that just means specific traits are high and others are low.

 

[HeavyHanded]

To me they are almost opposite, but could be interpreted a couple of ways.

Edge retention being generally improved by higher RC and addition of carbides.

Edge stability being how well the edge survives impact and lateral loading (all other things being equal).


I've had relatively low RC steel take a glancing blow on stone and it left a torn but functional edge. A steel with better raw retention characteristics would have chipped out.

 

[Wowbagger]

First off . . . Bluntcut . . . you are AWESOME and I learn a lot but due to the difference in language / translation I often feel like I should receive a paycheck after reading a string of your posts.

Keep up the great work though and I will get better at reading them.

Now . . . here was a huge eye opener that happened to me many years ago concerning the apex strength verses edge retention. I think as we get into better steel perhaps there is less of a difference.

I started out with Swiss Army knives for my first real knife because my mentor was all about them. I did get flumexed because way back in the day when I was FINALLY able to get an edge that would actually cut stuff it would get dull in very little time.

Wind forward to a decade or so ago when I was getting hair whittling edges on my wood working tools that with a change of a few degrees I could fine tune to last very well with little chipping or rolling.

The SAK still sucked even though I got sharp edges on them faster and sharper edges than when I was a kid. Then one day I went APE and rebeveled from that stock, monster wide edge angle, what is it like thirty degrees perside ? ?! ! !. And went like ten degrees per side. Dang thing lasted really well and cut stuff like no body's business. Apex stability tanked didn't it you may ask. Nope . . . able to cut pretty serious wire ties over and over with no damage to the edge.

I'm still scratching my head.
I just know it worked.

PS:

I really like learning new things/ideas/topics and not afraid

As Nick Shabazz would say “That’s a beautiful thing”.
Way to go !

 

[Steel_Drake]

Can we talk about the difference between "apex stability" (AS) and "edge retention" (ER)?

As I understand it, the two concepts are roughly as follows:

Apex stability is a specific material property of steel and is defined as the ability of an apex to resist microscopic chipping and rolling, and as I colloquially understand Roman Landes work on the subject, is supposed to increase as the hardness of a steel increases, increase as the non-martensite phases of that steel decrease, increase as the austenite grain size decreases, increase as carbide size decreases, and increase as carbide volume decreases.

Edge retention essentially means how slowly the force required to make cuts of a certain type increases, or how long a knife can continue to make cuts of a certain type before its sharpness drops below a certain pre-defined threshold. Critical in that is that there is no absolute meaning for "edge retention" since edge retention in whittling wood, as measured by retaining the ability to make crossgrain pushcuts into newsprint is very different than edge retention in slicing soft abrasive media to a low sharpness stopping point.

Excelling at the first kind of edge retention will depend mostly on the ability of the apex to resist microscopic chipping and rolling, whereas the second kind of edge retention will normally depend much more on the abrasive wear resistance of the steel (assuming apex stability is high enough for the apexes tested not to experience premature failure through microscopic chipping).

So, going back to your mentioning 1095 and 10V: I would expect 1095 to have higher apex stability, and 10V to have a lot more wear resistance. So I would expect high hardness 1095 with a grain size minimization focused HT to excel in types of cutting where the primary wear mode is likely to be microscopic apex chipping or rolling (e.g. food prep on a cutting board, whittling, clamshell packaging, zip ties), and I would expect 10V to excel in types of cutting where the primary wear mode is likely to be abrasive wear (e.g. clean cardboard, clean rope, clean carpet, etc.).

So the answer to which will have better edge retention is "it depends, in what type of cutting measured by what standard?"

 

[bucketstove]

Someone besides this guy ^. Apex stability vs edge retention. What are the differences.

Hi,
They're the same thing? One is just more specific
edge/apex stability - edge retention on a push cut
edge retention , sharpness retention, sharpkeeping, can be on a slice or push cut

 

[DeadboxHero]

This is a good discussion for all of us nerds here hahaha

When I think of edge stability, I think of high yield strength, a component of edge retention

When I think of edge retention I think about the complete package, the yield strength, tensile strength, the elastic and plastic deformation, ductility, impact toughness, corrosion and wear resistance.

problem being that we can only enhance a few components at detriment to others and that the USE of the alloy determines WHAT attributes to focus on.

That is the reason we all cant agree.

the best edge holding axe steel and heat treatment makes for a poor edge holding folding knife. The folder would not have enough strength, corrosion and wear resistance to hold a great edge.

the best edge holding 8" knife chef steel and heat treat would not make the best chopping blade. The Chopper would not have enough toughness, and ductility to hold a great edge.

also steel with high wear resistance is a poor choice for a straight razor.

its interesting to look at all types of cutting tools rather then only looking at just folders and fixed blades to understand.

 

[me2]

Apex or edge stability is just a measure of strength when the cross section is similar in size to the components of the microstructure. A sharp edge is on the order of 1 micron thick. Carbides and other structures in steel are frequently along the same order in size.

Edge retention is how long a steel/blade maintains a given level of sharpness. I typically remove cutting ability from this definition but some do not.

 

[Wowbagger]

DeadboxHero,
I almost didn't recognize you. You changed your avatar. Cool; the real you.

SamuriStuart,

Seems like there is a 3rd term associated with the other 2, but it escapes me at the moment.

I got it . . . the all important : Sharpness (ease of cutting if you will). My favorite.

I should elaborate on the Swiss Army knife edge I was talking about earlier. Specifically this knife. Third from top but I have since ground the other edges shown to match.
I'm very happy with the apex stability and edge retention considering this is some relatively soft blade steel.



Now with the factory edge, which I sarcastically call 30 degrees per side, ok in reality it is probably no more than 29° per side. :grumpy:

When they put this edge on the Swiss Army Knives all I can figure is they wanted the user to be able to baton building bricks with it with no edge profile damage. Well they succeeded. Cutting anything else more in the main stream though is . . . well . . . less wonderful than it could be.

Where as Ultimate Sharpness = as wonderful as can be.

Until I reground it and used it I would never have dreamed that the edge retention would actually lengthen. Stay sharp longer. Much longer. Much, much longer.

There is a youtube explaining how this works. A much thinner apex profile can wear further before the edge gets significantly fatter/duller. Where a wide angled fat edge gets dramatically fatter/duller with very little wear.

Sure the thin edge profile is less resistant to deformation but since I batton fewer bricks than most I am ALRIGHT with a thinner/sharper edge.

And I have never reached the point where the profile was too thin and weak. But I did reach the point where I could cut stuff like I needed to so that was where I stopped laying the angle shallower.

I have to cut the ends of thick, very soft, rubber tubes square and cosmetically clean and I can do this now. Easily. I put oil on the blade and on the rubber so the rubber doesn't grip the side of the blade and distort the tubing being cut but . . . it works well.

AND I can still easily cut through, slice through, hard wire ties that are pretty large with no edge damage. I can't even do that with a more robust edge angle when using ZDP-189 . . . the edge can chip if my angle of attack isn't square to the tie strap.

Now THAT IS apex stability.

What's not to like ? ? ? ! ! ! !

Sure the ZDP-189 edge lasts longer cutting abrasive materials and may even take an ever so slightly sharper edge but this shallow angle on the SAK took it from a knife I loathed to use to one I enthusiastically reach for.

So I recommend starting with insanely shallow edge angles for superior sharpness and then micro beveling wider if the edge rolls or chips. Edge retention, meaning retaining sharpness as the edge wears can come with a shallow edge angle. A shallower thinner edge profile can even enhance edge retention. Some of it depends on the person using the knife. I am very sensitive to what the edge is doing and avoiding banging into things that are not good for the life of the edge; staples and rocks and hard backing surfaces (think marble "cutting boards").

Apex Stability : ridged enough edge shape (geometry) to maintain shape under cutting loads and impact on material intended to be cut.

Edge Retention: yes the same thing but also abrasion/wear resistance. AND a profile conducive to retaining sharpness after some edge abrasion/wear.

Sharpness: ultimate sharpness = minimum acuteness (can this be called acuity ?) of angle geometry of edge that boarders on break down of Apex Stability.

 

[bodog]

Like I said, same thing but people attaching different traits to make them mean something different.

If you want to discuss what most people mean then it goes something like:

Apex stability= hard, tough steel with very fine grain and low carbide volume

Edge retention = hard steel with strong matrix and high carbide volume meaning super high wear resistance.

But again. Those are just people attaching different traits to the same concept. An edge that lasts.

High performance vehicle vs. Premium automobile. What does that mean? Well, high performance vehicle means a vehicle that can traverse rough, rocky, off road trails and premium automobile is something that can beat all others as a day to day driving vehicle on the German autobahn.

There, I just did the same thing to cars that people are doing to the phrases apex stability and edge retention. Taking certain specific traits and attaching them to different phrases that are really just generalized concepts that are actually the same thing.

In reality "high performance vehicle" and "premium automobile" are essentially conveying the exact same concept. High grade modes of transportation that perform in their given field better than whatever else is available. And if someone wants to argue about which "high performance vehicle" is the best at a given task than the general phrase "high performance vehicle" needs to be abandoned in favor of describing which environment you're talking about and which specific traits make it a "high performance vehicle" instead of assuming that the phrase "high performance vehicle" references ONLY off road Baja racing, which it clearly doesn't. It can be attached to many vehicles designed for a variety of environments. The same thing applies to "premium automobile." Or "edge retention." Or "apex stability."

Those two phrases are general concepts that really are just marketing terms for specific steels with specific heat treatments. They essentially mean nothing and everything at the same time. They're just referring to edges that stay sharp just like the the marketing phrases for cars just mean transportation that gets you from point a to b the best. However you define your transportation desires will be different than someone else and could become an argument over which is better, a ford raptor or audi a5. Or which is better, 52100 at 67 RC with a thin grind and phenomenal heat treatment or 10V at 65 RC with a thin grind and a phenomenal heat treatment or 3V at 61 RC with a thick grind and phenomenal heat treatment. Those three steels will all have high apex stability and edge retention given the right environments and all will have low apex stability and low edge retention given other environments.

If someone really wants to talk about what makes something have better apex stability or edge retention then they can only define what environments they're using and who will be using them and how they'll be used in that environment. Otherwise it'll be a pointless debate because as sure as the sun rises in the east and sets in the west, someone will present a hypothetical environment that will nullify the original statement that X steel has good apex stability or good edge retention. You know why? Because they're both vague "marketing" terms.

Cliff stamp says that S125V has low apex stability carving hardwood because the edge crumbles faster than A2 in that environment. Jim Ankerson says S125V has high edge retention because it cuts a lot of rope. A lot of people read that and say, golly gee whiz, S125V has low apex stability but high edge retention and A2 has high apex stability but low edge retention. Well, cliff stamp was right and Jim Ankerson was right, and they were wrong also. The only people that are wrong all the way around are the people who only hear what they want to hear and then misrepresent what was stated by cliff stamp and Jim Ankerson by saying apex stability and edge retention mean something different. What they SHOULD be saying is S125V has an edge that lasts a long time given certain parameters and A2 has an edge that'll last a long time given other parameters. And then define the parameters. What are you talking about? Chopping a knotty pine? Planing clean oak? Cutting dirty cardboard? Thin edge angles? Thick edge angles? Perpendicular cuts or cuts with a lot of side loading? Draw cutting? Push cutting? Etc, etc, etc.

Which edge stays sharpest the longest? Tell me what you're planning on doing and how you plan on doing it and for God's sake, don't argue about which steel has the highest apex stability or highest edge retention. They mean nothing. Talk about real, quantifiable traits, not vague marketing terms.

 

[samuraistuart]

All of you, well MOST of you anyway, thank you that does help me clarify maybe what the differences are in these terms that are being used.