Maximizing Edge Retention – What CATRA Reveals about the Optimum Edge

Edit: Normally I'd leave up my older posts, incorrect or not, for chronological viewing. I keep getting responses to older posts though that have already been corrected because folks aren't reading to the end of the thread before replying. It's ok. I've done it too.

Suffice it to say I misunderstood the parameters of the test and made incorrect judgements based on that incorrect understanding. My bad. Let's move on.
 
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T.L.E. Sharp said:
I'm not sure this test truly reflects the variables. It's a slicing cut, yes, but it's done under load it looks like. The cards resting on the edge bend as though a force is being exerted.
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I would like to see an example of your forceless cutting method.

When the machine slides forward and backward it also drops. So it's splitting the cards rather than cutting them. Of course an acute edge angle will last longer.
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If the machine didn’t “drop” the cards it would be cutting air.

In the real world though edges also experience lateral forces, slicing not under load, impact, etc.
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CATRA is a wear test. Other tests can be performed for lateral forces or impact. You can even perform your “real world” tests. How much lateral force would we apply? For what duration and how often? Would we periodically impact the blade in the middle of cutting? There is no one “real world” to simulate. Doing one test does not eliminate the possibility of performing others.
The result of that test is definitely the result of that test, but I wouldn't go putting a super acute edge on your survival knife and expect to hack your way through a forest.

I'm glad I didn't put any money into that experiment.
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There are often people who seem very quick to dismiss different forms of testing as not being “good enough” for whatever reason seemingly to dismiss any findings that are found in the test. I don’t understand that need for ignorance.
 
Larrin said:
Don’t think I forgot about the effect of steel, that is what I do for a living. That article will come.
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I didn't think you forgot, but I also felt that it wouldn't hurt to state my interests. I am looking forward to the article.
 
T.L.E. Sharp said:
I'm not sure this test truly reflects the variables. It's a slicing cut, yes, but it's done under load it looks like. The cards resting on the edge bend as though a force is being exerted.

When the machine slides forward and backward it also drops. So it's splitting the cards rather than cutting them. Of course an acute edge angle will last longer.

In the real world though edges also experience lateral forces, slicing not under load, impact, etc.

The result of that test is definitely the result of that test, but I wouldn't go putting a super acute edge on your survival knife and expect to hack your way through a forest.

I'm glad I didn't put any money into that experiment.
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I look at this test as I do most of the others. It gives me some insight about the alloy at a given hardness and HT protocol. Since the same hardness can be achieved but one with a non-optimal HT with two different knives, it stands to reason that if these knives are Heat treated to "industry standard" or Manufacturer suggestion, that doesn't necessarily mean it is done to the "knife industry" standards.

This subtle difference will result in two knives that react noticeably different, while both being of the same measured hardness.

I look at all "tests" through the same light. It gives me an idea of how one alloy may compare to another, but only in one facet. Not how it reacts to "real world" usage, but in absolute toughness, edge retention, corrosion resistance to a certain environment or element, etc.

This test just helps us make a more informed decision of what we want from our knives. It does not tell us the definitive, end all be all result to an alloys wear resistance.

If you are cutting cardboard, you may not notice a difference, but smack a staple, and the CPM variant may be just be tough enough to not suffer a chipped edge.
 
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Edit: Normally I'd leave up my older posts, incorrect or not, for chronological viewing. I keep getting responses to older posts though that have already been corrected because folks aren't reading to the end of the thread before replying. It's ok. I've done it too.

Suffice it to say I misunderstood the parameters of the test and made incorrect judgements based on that incorrect understanding. My bad. Let's move on.
 
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Larrin said:
New article on a never-before-published CATRA study which looked at an impressive number of variables, including edge angle, edge thickness, cryo, powder metallurgy, hardness, and sharpening grit, all with 154CM and CPM-154. What makes an edge cut the longest?

https://knifesteelnerds.com/2018/06/18/maximizing-edge-retention/
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Thank you for the data, I enjoyed reading through it a few times.

“So it appears that with a lower angle edge it can wear down to a larger apex and still maintain better sharpness than a higher angle edge.”

Pretty interesting! Thanks for the time and work, I look forward to reading future tests.
 
I care not about at least 95% of what the article contained (and understood less), but the pics were cool. I mean that in the nicest possible way, but the data is just over my head.

It’s cool that many of you are into steels and edges to this level though. Larrin Larrin has likely forgotten more about metallurgy than I will ever know. :thumbsup:
 
SharpieB said:
I care not about at least 95% of what the article contained (and understood less), but the pics were cool. I mean that in the nicest possible way, but the data is just over my head.

It’s cool that many of you are into steels and edges to this level though. Larrin Larrin has likely forgotten more about metallurgy than I will ever know. :thumbsup:
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I use as many images as possible in the articles for a reason. :)
 
Twindog said:
What did surprise me is that edge width at the shoulders had such a small effect. Both edge widths - 0.01 inches and 0.02 inches are well narrower than the edge width of typical production blades. And the report says that there was considerable variance in edge widths because they were ground by hand.
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I think this is dependent on the cutting material. On the catra all the little pieces of paper just fall when they are cut. If you are cutting say, cardboard you still have the cardboard on each side of the apex until you get closer to the end. A geometry that decreases friction will make it easier to cut through that type of medium. However I'm wondering about batoning for example... The wider geometry is used for splitting instead of the tip after the initial chop. Would a wider behind the edge help edge retention on some materials due to taking the pressure off the tip? Then again were trying to test edge retention, and silica paper is probably idea for this.

I like cpm154 it's great to use cutting but it will dull before m390 will, I'll have to try a more acute angle and see if I can make it last longer. The maxamet mule I have is still factory angle and it goes forever and it's fairly obtuse. I'm gonna have to compare it to my maxamet pm3 with a more acute angle.
 
Dangerously said:
Though it’s not the way the industry has been moving, there have been people out there preaching the merits of acute edge angles and easy-to-sharpen steels for a while. My personal experience has also been leading me to the same conclusion, although without scientific rigour.

Thanks for posting this, Larrin.
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CedricandAda has been showing exactly this in some of his recent videos,
 
As Roman Landes says, “Geometry cuts, steel determines for how long”. That’s why now my favorite steel is AEBL, as Larrin pointed in his tests (and Landes years before), this steel is so tough that can be made incredibly sharp without chipping, much sharper than those loaded of carbides “super steels”, and is Stainless, as a bonus! Most people (like me, in the past) didn’t care about it because it’s cheap and ultra alloyed steels were fashion, but now, thanks to Metallurgists (Larrin, Landes, Haakonsen), I see the light!
 
My father was using AEB-L in the 90's in his damascus and promoted its properties for years. Landes usually gets the credit for bringing it to the forefront though. Maybe he was more successful in promoting it.
 
Larrin said:
My father was using AEB-L in the 90's in his damascus and promoted its properties for years. Landes usually gets the credit for bringing it to the forefront though. Maybe he was more successful in promoting it.
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Landes and Devin Thomas, years before Larrin, reached same conclusions. My apologies to mr. Devin Thomas.
 
Larrin said:
New article on a never-before-published CATRA study which looked at an impressive number of variables, including edge angle, edge thickness, cryo, powder metallurgy, hardness, and sharpening grit, all with 154CM and CPM-154. What makes an edge cut the longest?

https://knifesteelnerds.com/2018/06/18/maximizing-edge-retention/
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What I found super interesting is that it looks like 600 grit with DMT diamonds was the “best” edge and when pushed up to 8000 grit dmt the edge seemed to take alot of damage. I had often heard that the highest finishing grits should be done with diamond stones so they can cut the carbides. However the article states that the better edge was achieved when using softer stones for the finishing grits.

Dmt 600 grit edge
600-grit.jpg


8000 dmt grit edge
8000-grit.jpg
 
hugofeynman said:
As Roman Landes says, “Geometry cuts, steel determines for how long”. That’s why now my favorite steel is AEBL, as Larrin pointed in his tests (and Landes years before), this steel is so tough that can be made incredibly sharp without chipping, much sharper than those loaded of carbides “super steels”, and is Stainless, as a bonus! Most people (like me, in the past) didn’t care about it because it’s cheap and ultra alloyed steels were fashion, but now, thanks to Metallurgists (Larrin, Landes, Haakonsen), I see the light!
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It's risky to critique Landes -- or Devin Thomas -- but it's more complicated that that quote. Geometry cuts, but it's the characteristics of the steel that determines how much geometry your blade can support. Heat treat, added elements and steel processing also affect how much geometry the edge can support, as well as determine how long it cuts.

My most used kitchen knife has an AEB-L blade, and I like it a lot. But its wear resistance is poor. Yes, it can get sharp, but so can any steel. Rockstead's ZDP-189 or YXR7 blades come extremely sharp. Diamonds are harder than any carbide they'll encounter on an edge, so with proper technique, there is no reason that any steel can't get super sharp. And because the new high-tech steels can support more aggressive edge geometry, they can also be easy to resharpen with diamonds because there is much less steel to be removed on their thin edges.

AEB-L is a tough, stainless steel, but that doesn't mean it won't roll or dent or deform if your work exceeds the geometry that it can support. At that point, you switch to a better steel so you don't have to give up high-performance geometry.
 
Lapedog said:
What I found super interesting is that it looks like 600 grit with DMT diamonds was the “best” edge and when pushed up to 8000 grit dmt the edge seemed to take alot of damage. I had often heard that the highest finishing grits should be done with diamond stones so they can cut the carbides. However the article states that the better edge was achieved when using softer stones for the finishing grits.

Dmt 600 grit edge
600-grit.jpg


8000 dmt grit edge
8000-grit.jpg
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Edit...
Those images were from https://scienceofsharp.wordpress.com/2015/03/01/the-diamond-plate-progression/
For context.

When I was researching stones for mirror edges years ago, the threads here said this was not an idea stone to use and the sem images prove this as you mentioned. Doesn't necessarily mean all diamond stones or strops will leave that type of finish.

Here's some data taken from numerous stones including the dmt 8000 and why it's more coarse. Probably not idea for a finishing stone.

https://scienceofsharp.wordpress.com/2016/12/21/abrasion-rate-vs-grit/

While this is the 1200 https://scienceofsharp.wordpress.com/2015/09/28/diamond-plate-break-in-part-2/
The 8000 may have similar layout causing the damage seen in the photos.
 
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