Maximizing Edge Retention – What CATRA Reveals about the Optimum Edge

Really interesting that the more acute (vs obtuse) edge angle "won". (See the comment below for obtuse and acute sharpened angle/apex. I don't want to have misleading stuff in threads if possible.) 600 grit DMT (fine) created the most usable edge and lasting edge. Quote is from the study conclusions.

"From this study it should be apparent that lower edge angles lead to superior cutting performance. PM vs ingot, cryo, and edge finish appear to be minor factors; Minitab analysis seems to put the contribution to edge retention solely on hardness rather than the PM/ingot difference. Hardness and edge thickness have less effect than edge angle but are still important."

I might add that it may appear that the recent focus on "super steels" at high hardness may not be all that significant relative to cutting performance. The study used CPM-154 and CM-154 (crucible vs igot produced steel). Differences may be barely measurable and likely not observable to a normal knife user.

(Sorry I keep adding to this post. I edited my initial obtuse comment. I missed that in my initial skimming the article and then mostly looking at the conclusions first.)
 
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Larrin said:
I believe you mean the more acute angle was the winner.
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I believe I did although when someone talks about actual edge angles and then in the conclusions says "low" or "high" it is misleading or less clear to me. Again from the study below....

"You can see that the initial cut length with a smaller angle is considerably higher and that the difference holds basically to the end of the test. This finding is significant because some have speculated that lower angle edges start out sharper but a more obtuse edge lasts longer [2]. And with the high wear that occurs in the CATRA test it isn’t likely that the situation would reverse with even further cutting. The initial blunting rate is relatively rapid regardless of angle and it then begins to level out."
 
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.
 
22-rimfire said:
I believe I did although when someone talks about actual edge angles and then in the conclusions says "low" or "high" it is misleading or less clear to me. Again from the study below....

"You can see that the initial cut length with a smaller angle is considerably higher and that the difference holds basically to the end of the test. This finding is significant because some have speculated that lower angle edges start out sharper but a more obtuse edge lasts longer [2]. And with the high wear that occurs in the CATRA test it isn’t likely that the situation would reverse with even further cutting. The initial blunting rate is relatively rapid regardless of angle and it then begins to level out."
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Yes, for this article acute, small, and low are synonyms while high, large, and obtuse would be the opposite.
 
What can I say? To me, high means acute or a fine angle... a steep or high angle.... Thinking further about the analogy, a high slope (steep angle) would actually relate to "obtuse" versus acute. It is kind of like tip up and tip down carry which still confuses me when a clipped knife is closed in your pocket.

But I have modified my original post so that some one reading this does not form the incorrect conclusion relative to the study with the two steels.
 
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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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Personally, I don't mind a more difficult to sharpen steel if it lasts a lot longer between sharpenings. But very good to know some scientific testing results behind tweaking an edge for optimal performance in an easy to sharpen steel as well.
 
Interesting conundrum with the word "acute." When describing an angle, "acute" simple means between O degrees and 90 degrees. Once an angle falls somewhere between 0 and 90, it is no more or less acute than any other angle falling in that range. In other words, there are no degrees of "acuteness" in the geometry sense.

However, outside the geometry world, "acute" also means "severe", "intense", or "urgent", etc. Thus "acute" is sometimes used to mean a "severe" or "sharp" angle. Which is not necessarily an incorrect use of "acute" in its second meaning.

Confusion can arise when one person is talking about the angle of the apex of a knife blade, i.e. using "acute" in the geometry sense, and in the same conversation another person is talking about how sharp a knife is, i.e., using "acute" in its second meaning.
 
shinbone said:
Interesting conundrum with the word "acute." When describing an angle, "acute" simple means between O degrees and 90 degrees. Once an angle falls somewhere between 0 and 90, it is no more or less acute than any other angle falling in that range. In other words, there are no degrees of "acuteness" in the geometry sense.

However, outside the geometry world, "acute" also means "severe", "intense", or "urgent", etc. Thus "acute" is sometimes used to mean a "severe" or "sharp" angle. Which is not necessarily an incorrect use of "acute" in its second meaning.

Confusion can arise when one person is talking about the angle of the apex of a knife blade, i.e. using "acute" in the geometry sense, and in the same conversation another person is talking about how sharp a knife is, i.e., using "acute" in its second meaning.
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Grammar is hard! The word "acute" is not used in the article, and obtuse is only used once with the reference to a "more obstuse" angle.
 
It always amazes me how complex knives are, when they seem like such simple tools.

I would not have expected that much difference between CPM 154 and 154 CM on wear resistance because the biggest advantage of powder-steel technology is added toughness compared to its ingot counterpart, not edge wear. Powder steels allow for a much higher load of carbides while still being tough enough to use as a knife. High carbide loads in an ingot steel will cause that blade to be prone to breakage. So this part of the experiment doesn't seem to have much value.

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.

I'm going to take this finding with a grain of salt. In my experience, edge width is a major factor in how well an edge cuts and for how long. I think Ankerson's tests show that, too. I have a knife made by Luong (Bluntcut) that is 0.006 inches wide at the shoulders, and it cuts through cardboard like a laser. It's almost like cutting air. None of my knives with edge widths of 0.02 inches or wider can come anywhere close to that performance.
 
Soooo ... Do these results apply to "lesser" steels, like the 440 series, 420HC, 10xx, and so on, at their optimal hardness?
 
Twindog said:
It always amazes me how complex knives are, when they seem like such simple tools.

I would not have expected that much difference between CPM 154 and 154 CM on wear resistance because the biggest advantage of powder-steel technology is added toughness compared to its ingot counterpart, not edge wear. Powder steels allow for a much higher load of carbides while still being tough enough to use as a knife. High carbide loads in an ingot steel will cause that blade to be prone to breakage. So this part of the experiment doesn't seem to have much value.

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.

I'm going to take this finding with a grain of salt. In my experience, edge width is a major factor in how well an edge cuts and for how long. I think Ankerson's tests show that, too. I have a knife made by Luong (Bluntcut) that is 0.006 inches wide at the shoulders, and it cuts through cardboard like a laser. It's almost like cutting air. None of my knives with edge widths of 0.02 inches or wider can come anywhere close to that performance.
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I agree it is surprising the relatively smaller affect of edge width relative to angle. However, there is some correlation between edge width and angle with a typical knife that does not have such a controlled angle as in this study. A thicker edge with a 20° angle has a very tall edge which you are unlikely to ever see. Also, the range of edge widths was narrow in this study. I think a wider range of edge widths would be interesting as I said in the conclusion.
 
Thank you Larrin Larrin .

What I would like to see is three vastly different alloys with a comparable thin cross sectional measurement BTE. Say Buck 420hc, M390/204P/20CV (or Busse Elmax), and Maxamet all ground to around .01" BTE and see how the actual alloys fair.

Due to .01" not being that drastic of a measurement, but still allowing for decent geometry, I would like to see how they stack up with such a wide gap between the alloys, in regards to edge retention.
 
NJBillK said:
Thank you Larrin Larrin .

What I would like to see is three vastly different alloys with a comparable thin cross sectional measurement BTE. Say Buck 420hc, M390/204P/20CV (or Busse Elmax), and Maxamet all ground to around .01" BTE and see how the actual alloys fair.

Due to .01" not being that drastic of a measurement, but still allowing for decent geometry, I would like to see how they stack up with such a wide gap between the alloys, in regards to edge retention.
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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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