Maximizing Edge Retention – What CATRA Reveals about the Optimum Edge

Ooh, I'm getting my reading glasses and a sammich.

....Just read it. Very interesting. Shocking to see the difference between 600 grit edge finish and 8000 grit. Never would have expected that.
 
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That's really interesting. And some of it surprising to me. Geometry - no surprise. Such a negligible difference between PM and ingot that the minor RC variation could account for all of it? Big surprise to me.



What is the cost involved with having a CATRA study like that done? Outside of the knife prep - just the testing costs?
 
did a quick read and as i understand the cryo blades were tempered to 1000f seems counter as to why to cryo at all. cryo wodl get rid of most the RA but then at 1000f you wodu be in the secondary hardness curve and precipitating carbides. i know its to keep things as apples to apples but woudl it not be better to quench from a lower temp then cryo and temper in the first range?
 
kuraki said:
What is the cost involved with having a CATRA study like that done? Outside of the knife prep - just the testing costs?
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The primary costs associated with the study described in the article were shipping, and the flight costs of the sharpener (Jason B). Much of the rest of the work was donated. The testing itself was done at a knife company that owns a CATRA and requested to not be named. Costs for tests by CATRA are approximately $75 per test plus the cost of shipping to Britain. So usually the costs are steel, heat treating, making the knives, sharpening, running the tests, and shipping between all locations. With donated materials, services, etc. that can bring down the cost but even then it gets expensive fast.
 
butcher_block said:
did a quick read and as i understand the cryo blades were tempered to 1000f seems counter as to why to cryo at all. cryo wodl get rid of most the RA but then at 1000f you wodu be in the secondary hardness curve and precipitating carbides. i know its to keep things as apples to apples but woudl it not be better to quench from a lower temp then cryo and temper in the first range?
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I pointed out in the article some of the potential pitfalls of the cryo being performed in the way that it was, but I'm not sure there is anything cut and dried when it comes to cryo.
 
Holy crap! Are those pictures in the right order? Something's gotta be wrong with that DMT 8000.

SABELSS.png
 
SirSpice said:
Holy crap! Are those pictures in the right order? Something's gotta be wrong with that DMT 8000
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Nope.

https://scienceofsharp.wordpress.com/2015/03/01/the-diamond-plate-progression/

ETA: I mean, there may be something wrong with a particular DMT 1200+ grit plate. The one I bought looked like someone had gone over it with a needle scaler before the diamond was applied, so the first knife I stroked across it shaved off a bunch of steel volcanoes :mad: But, those images are consistent with what's in the SoS blog.
 
SirSpice said:
Holy crap! Are those pictures in the right order? Something's gotta be wrong with that DMT 8000.

SABELSS.png
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Read the article from the referenced Science of Sharp blog and you can see if you find his description convincing.
 
In all my years of looking at edges, I always told people that geometry cuts. The steel's job is to try to maintain that geometry for as long as possible. Nice to see that there is some definitive data to back that up.
 
Larrin said:
Read the article from the referenced Science of Sharp blog and you can see if you find his description convincing.
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I read the SoS article, very interesting. By the way, I wasn't doubting you. I was just surprised. Great article.
 
Very interesting article for sure. I am shocked that edge angle has such an impact on edge retention vs actual behind the edge thickness. I would think that if an edge was .005"/30° inclusive that it would have better edge retention than an edge 0.015"/20° inclusive (all other things equal). But I guess I would be thinking wrong! I also found it interesting that the 600 grit/mesh edge peaked in the tests. I've always felt that the edge of the 600 grit/mesh plate felt the sharpest of all the diamond plates. It just fells the sharpest to my fingers when checking a freshly sharpened edge, again all things equal.
 
Wow. Very interesting.

I was not surprised to see the minor effect of edge thickness in this test with the thin cut medium (card).
But I was really surprised by how small the effects of hardness and edge finish are!
 
miso2 said:
Wow. Very interesting.

I was not surprised to see the minor effect of edge thickness in this test with the thin cut medium (card).
But I was really surprised by how small the effects of hardness and edge finish are!
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I think there would be a bigger difference from hardness if there was more than a 1 Rc range.
 
My favorite article so far. Once work stays steady for a few weeks I will sign up for your patrion. I really appreciate the work your putting in. I also love the idea of crowd funding research just for the good of the craft.
 
thank you for posting this article. I think hardness here is close enough to call even because of machine tolerance. it was curious or just the way things happened that the lowest angle also used to lowest grit. was interesting to see little difference between ingot and CPM steel, as both versions have been forged and rolled numerous times between foundry and final sale. good starting point for more tests.
 
I thought I was crazy, but my super fine edges seem to stay sharp way longer than the recommended “durable” geometry. I thought this testing would have corrected my experience.

I think it would be interesting to see what happens on a steel that is not as hard, or unable to support such a fine edge. Something like 5160 in the mid to high 50’s. I’ve been using W2, 52100, AEb-l, 15n20 and z-wear/cru-wear for most of my knives. I had a weird experience with an 8670 kitchen knife at Rc63 that the owner insisted outperformed a very nice W2 knife I made, also at Rc63. He noted in the comments that the 8670 knife was noticeably thinner behind the edge. He said he got 20% better wear resistance with the 8670 knife than the W2.

Larrin, if I’m reading this right, pick the steel and hardness that gives you the most stable fine edge, and optimize the heat treat for that to get the best wear resistance? The steel that supports the finest edge will give you the longest lasting edge?
 
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