Managing expectations of edge retention

Cushing H. said:
Again, i did not say i did not believe it …. I said basically i would not take it as gospel until or unless i saw clear statements of experimental setup and the resultant data. If i “scroll up”, what i see is (well intentioned) anecdotal statements that in themselves raise questions.
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no... if you scroll up you'll see an actual statement from Roman, himself, regarding his study. If someone speaks about the experiment THEY ran, that was peer reviewed and published... it's not fucking anecdotal. What the fuck is happening?
 
Cushing H. said:
Oh my … so much for clear and forthright discussion on data and related information.
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The devil is in the details, right?
You're not wrong to question the experimental method.
That's why such a large part of the scientific method is dedicated to explicitly on the procedure.

Rick Marchand said:
At some point you have to believe that the goddamn experts know how to do their job. This is insane. People like, Roman and Larrin, most likely know how to conduct an experiment, with regard to their own fucking profession. So lose the contrarian filter and save the word salad for your discussion with, Roman.

I'm unfollowing this thread, for my own mental health. Enjoy.
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I'm very interested in the topic- you just happened to be the bearer of the news, so forgive me if it feels like an attack.
I'm interested because 90% of the sharpening that I've done my whole life has basically been on dry diamond stones.
If what you say is true, I've been using sub-optimal edges for decades.
 
EngrSorenson said:
I concur. There are so many variables at play that, although perhaps peak temperatures is localized spots reached 3632 F I would find it hard to believe that there's any practical change in the metal. Even if there was, the test itself would be so hard to conduct in such a way to account for everything.


For instance, the surface area of the block touching the sand paper was likely 8 square inches. Significantly larger than the size of the average bevel.
I would have also been interested to see if there was a pattern in the temperatures- I would guess that the back of the block would have the highest temperatures, as it's crossing over sand paper that has already generated heat from friction.
I would be interested to know if the sand paper was insulated.
I would want to know how fast the block traversed the sand paper (and in what orientation).
a 2x2x4 block of steel is what... about 5 lbs? that would be a little more than half a pound per square inch. I wonder how good of an approximation that is for sharpening?
Like you said before, I'd also like to know how the experiment accounts for the Heisenberg uncertainty principle in the thermocouple measurements.

My day job is testing complex systems, so I know how experiments can be rife with problems.
The smaller a thing is, the harder it is to test- note that even here, the test uses a steel block as a surrogate for a knife bevel and I'm not sure that is a good approximation due to the changes in convective heat transfer and the total heat generated.
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What you said. I was trying to not get too nerdy … but what ran through my head was “what grit?”, “what contact area?”, “what pressure?”, “what speed?”, “do any of those relate to the conditions of sharpening?” and especially (as landes himself noted) there is a huge heat sink of metal around the contact point which will very very quickly dissipate the energy … so how the heck could a (relatively huge) thermocouple, removed from the point of contact register such a high temperature (unless maybe the thermocouple WAS the point of contact … which would invalidate the result)
 
EngrSorenson said:
The devil is in the details, right?
You're not wrong to question the experimental method.
That's why such a large part of the scientific method is dedicated to explicitly on the procedure.


I'm very interested in the topic- you just happened to be the bearer of the news, so forgive me if it feels like an attack.
I'm interested because 90% of the sharpening that I've done my whole life has basically been on dry diamond stones.
If what you say is true, I've been using sub-optimal edges for decades.
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Dan - i would tend to place a lot of credence in the trials horsewright related above. The “setup” appears very practical and directly related to sharpening. The “measured variable” does not try to be highly detailed or small-geometry, and is also highly related to real-world use-conditions. I think my takeway from that echoes what you already said above … whatever actually happens at the very small scale, within some reasonable range of the sharpening technique used it might very well make no real difference in practical usage experience….
 
Cushing H. said:
What you said. I was trying to not get too nerdy … but what ran through my head was “what grit?”, “what contact area?”, “what pressure?”, “what speed?”, “do any of those relate to the conditions of sharpening?” and especially (as landes himself noted) there is a huge heat sink of metal around the contact point which will very very quickly dissipate the energy … so how the heck could a (relatively huge) thermocouple, removed from the point of contact register such a high temperature (unless maybe the thermocouple WAS the point of contact … which would invalidate the result)
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and then from a metallurgy standpoint, time and temperature are both variables in temperament. Landes said he registered temperatures well above the melting point of steel, and yet the duration wasn't long enough to actually melt the metal- a concept I'm having a hard time understanding byself! The sniff test indicates to me that I either have to get this guy's book and understand the procedure, or give up completely because I have a day job (which interestingly enough is loosely related metals and prolonged exposure to extreme temperatures).
 
Cushing H. said:
Dan - i would tend to place a lot of credence in the trials horsewright related above. The “setup” appears very practical and directly related to sharpening. The “measured variable” does not try to be highly detailed or small-geometry, and is also highly related to real-world use-conditions. I think my takeway from that echoes what you already said above … whatever actually happens at the very small scale, within some reasonable range of the sharpening technique used it might very well make no real difference in practical usage experience….
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I concur- a simple test that's hard to repeat that generates lots of data can be valuable. It's not sophisticated, but it has credibility because I understand how it's accomplished and readily see the application.
Horsewright would never be able to quantify anything, but he can qualify that- in a practical sense- there's no difference between careful belt sharpening and hand sharpening.
Personally I'll stay away from belt sharpening for as long as I draw breath because I don't believe I'm skilled enough to not ruin my knife.

Now we're just missing the data that tells us if a knife sharpened on a dry diamond stone has an inferior edge to one sharpened on a wet stone.
 
And... it looks like I'm out of luck on heading straight to the source, since the language barrier will be more than troublesome.
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EngrSorenson said:
I concur- a simple test that's hard to repeat that generates lots of data can be valuable. It's not sophisticated, but it has credibility because I understand how it's accomplished and readily see the application.
Horsewright would never be able to quantify anything, but he can qualify that- in a practical sense- there's no difference between careful belt sharpening and hand sharpening.
Personally I'll stay away from belt sharpening for as long as I draw breath because I don't believe I'm skilled enough to not ruin my knife.

Now we're just missing the data that tells us if a knife sharpened on a dry diamond stone has an inferior edge to one sharpened on a wet stone.
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Interesting … ifind belt sharpening MUCH easier and harder to damage the blade. FWIW .. I use a 400 grit belt, spray it wet, use very very slow speed on the belt . Then i have my work rest in place , and on that rest have a little “jig” made out of MDF that defines a 15 degree angle from vertical. I rest the blade against that jig, then lock my hands holding the blade to that angle, remove the jig and take a pass along the edge. I repeat that for every pass.

My biggest problem with stones (for fifty odd years) has always been setting the angle consistently …. Both between and within strokes. The result does not cut well, and looks even worse 😒
 
Rick Marchand said:
The idea is to get the blade red hot before attempting to sharpen. That way, you are just pushing the molecules around to form an edge rather than removing molecules. The goal is to refine the apex to the width of one molecule. Then lock in the molecular structure by quenching it into an all-dressed potato(hold the chives). I feel the need to drive this home by saying "molecules" one more time.

Heh heh... Good post, Hoss. Most users, judge the quality of a knife by it's sharpness, edge retention and the type of steel it is made from. All of which mean nothing if the maker doesn't have an intimate knowledge of the mechanisms that govern those attributes. I will add my bit of advice.....

I cannot stress enough the importance of keeping that edge cool while sharpening. Lube, coolant, quality abrasives.... all will reduce heat build-up. Even hand sharpening on a dry diamond plate can overly temper the apex. This became surprisingly apparent to me, when I started making kitchen knives. I was a "220 belt, cork belt strop" guy when I was making choppers and camp knives. They were crazy sharp but I did not realize how much edge retention I was leaving on the table by my method. When I switched to setting my final edge with water stones and CBN plates (with plenty of water), I felt embarrassed.... don't tell the other guys, K?
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No no no you gotta hammer it together to compact the molecules. Thats why forged knives are #1

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DeadboxHero said:
C Cushing H. EngrSorenson EngrSorenson

Article came out a few months before you guys joined bladeforums in 2019 so you might have missed it.

knifesteelnerds.com

Does Sharpening with a Grinder Ruin Your Edge? - Knife Steel Nerds

You have to sharpen a new knife a few times to get it cutting well. Right? Or do you? Are knife manufacturers improperly sharpening their knives?
knifesteelnerds.com knifesteelnerds.com
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Fabulous article, written by a real expert.

I'm a little disappointed it didn't get into non-lubricated hand sharpening, but sadly I think that's to be expected.
I'm honestly not surprised by the results, but it was fascinating to read how close to the apex one could measure hardness.
As a life long hand sharpener, I've seen enough to carry on in my ways.

As of late, I've been using the Baryonyx stones and water for all my sharpening.
 
Well there's other factors as to why the edge could not be as sharp from not using lubricant such as the stone simply clogging with the cut metal filings preventing the abrasive from doing its job further hence being left with an edge that is not shaped as nicely and exhibiting more convexity of the apex radius from burnishing and deformation damage.

I don't think anybody is arguing that you need water to prevent your edge from overheating with a hand sharpening stone.

It's just that the water is important for the functioning of the sharpening stone to remove metal filings for it to actually function on a fundamental level.

Water is however extremely important as a COOLENT for belt sharpening to help prevent micro tempering of the apex which will reduce the cutting edge retention and also may force the end user to remove the burnt steel when they decide to hand sharpen their knif. Finer belts generate more heat. Worn belts also generate more heat.




EngrSorenson said:
Fabulous article, written by a real expert.

I'm a little disappointed it didn't get into non-lubricated hand sharpening, but sadly I think that's to be expected.
I'm honestly not surprised by the results, but it was fascinating to read how close to the apex one could measure hardness.
As a life long hand sharpener, I've seen enough to carry on in my ways.

As of late, I've been using the Baryonyx stones and water for all my sharpening.
Click to expand...
 
A little physics. Any forceful separation of material is accompanied with heat. The faster and wider, more heat. So smaller particles and dispersed more will generate a lot less heat then large particles in a crowd. Heat is inevitable and can't be avoided with any method. Even if it's slow and cooled with LN spray it will still generate heat at the tear. Point is to avoid the threshold not to generate too much that it travels along. First micron can always be sacrificed. Light passes on a belt belt with cooling between passes works just fine. Direct cooling with a mist is better. Hand sharpening with average force will not get things better. It can be easily tested. Speed of the push even with a coolant will generate heat in that instance because generation is way faster than dissipation. All this from a point of one that cares, not from a point of general manufacturers as they don't sharpen, they grind and strop at high speed. Of course they burn stuff.
But, let's say there is a method that can achieve zero heat. You get a 50g BESS and it's gone with the first cut. Difference in 5HRC in that first couple of micron will be irrelevant for the speed of abrasion. Getting to the working edge and keeping it is more relevant. Larrin tested sharpness and it revealed that higher than 400 grit has little to no value. Essentially going higher gets problematic.
But :) for those who want to go beyond, there is a way to achieve it. My way to sharpen expensive kitchen knives soon to be is:
Sharpen with care how ever you want until small wire edge. Some heat will temper the surface and that's irrelevant. Next, electropolish the edge. It will remove first several microns and when thinning, the wire edge will be gone leaving almost a perfect edge. BESS 20g capable. How long will it stand true is another story. Electropolish cleans up the surface so any remainders of grinding is removed. Some particles can get stuck and push corrosion or pitting. Electricity rocks.

And, on the subject of mentioned definition. Seems like there is little thought to it. So I will call it from now on, "edge dynamic strength". Naming reveals a lot so there shouldn't be any confusion with first timers. Why is it important to me? Because I find the edge more important than the blade, and the blade is VERY important. Strength of steel related to geometry should be the main factor for choosing steel and heat treatment method. And when dynamic strength is calculated or measured it will be easy to refer to the appropriate use.
 
I would also question almost any reading of 2000C on a thermocouple. They virtually all are destroyed at lower temperatures since they may melt, or react chemically with their medium (e.g. burn up).

Thermocouples are fundamentally an electrical circuit that induces a micro volt change in potential at elevated temperatures. The voltage is strongly correlated to the temperature, so measure the voltage, convert to temperature, and done. Except, real life is a bit more complicated. The thermocouple bead has mass and surface area. It takes time to heat up, and it can lose energy to cool ambient surroundings if not fully embedded in a solid. You can correct for this with algorothms.

Even more tricky is electrical interference. If you place a TC on a conductive surface like steel, you just did 2 critical things. 1. You created another thermocouple (steel to bead) and 2. You created a more complex electrical circuit than just 2 wires welded together. So now, any voltage change in the steel will give you a spurious reading of temperature. It doesn't take much, we are talking micro volts. Grounding can help, but not always.

Plus, there can be other background interference issues caused by AC current devices near the TC, but they are generally small.
 
soooo....

back to the topic at hand; as D DevinT mentioned in a slightly unrelated thread "Design is everything"

when you design a knife, and you plan for how it's going to be used, you choose a thickness of steel that provides the optimal attributes for the intended design. You choose a width, based not only on the thickness you choose, but for the intended use as informed by your design. Then you choose the primary bevel angle(s) and choose where it/they will terminate toward the spine and toward the edge. Then you choose how far up that primary bevel your secondary bevel is going to go/your secondary bevel angle...

all these choices...

they determine so much more about how a given knife is going to perform at its given job than so many other factors that some of us are overly obsessed with, in this thread, at the moment. It would be cool to focus on these other things instead of the effects of sharpening heat has on an edge- which in my view is an entirely different conversation.

the choices made that go into the design of a knife are the most interesting topic, because it gives insight into how and why knifemakers do what they do, and why they are successful at making a good knife or not. Getting bogged down in all this mumbo jumbo is ruining a potentially very enlightening conversation. In my opinion.
 
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