When I was still fairly new to sharpening, I had experimented with stropping using a balsa wood strop pasted with a green aluminium oxide compound. I never got good results from it, and I quickly became familiar with the often complained of issues of stropping leading to a complete loss of slicing aggression, which I understand to be what is meant in general by "killing the edge" "excessive stropping" "overly buffed."
A while back, my interest in re-exploring the topic was piqued by some SEM images produced by the Science of Sharp blog in this post about burr removal. In particular, the idea of Mothers Mag & Aluminium polish on a hanging denim strop producing the pictured apex interested me.
Subsequently, I have tried a variety of stropping compounds and substrates in trying to see what results I could obtain. I've tried Mothers Mag & Aluminium Polish, 0.25, 1.0, 2.0 and 6.0 micron diamond pastes, and 8.0 and 16.0 micron CBN emulsions.
These compounds have been tried on hanging denim, hanging leather, and block mounted leather strops.
My goal was to explore whether pasted strops could make a viable alternative for creating and maintaining micro-bevels on my EDC knives, which I had previously been doing with a Spyderco Sharpmaker with the M or F rods.
In each case, I cut off the previous edge on the knife, and shaped the edge-bevel using a three-step sharpening method approach starting with my Sigma Power Select II 1,000x stone and then refined the edge on my SPS-II 6,000x stone prior to stropping.
I found that I had a much easier time precisely getting the angle I wanted and the contact area I wanted using block backed leather strops. This surprised me, as I had assumed the hanging strops would be easier to use, but I found it very difficult to get any consistency with the hanging strops. Conversely, I've found the leather bench strops fairly easy to use, but I probably have an advantage with that because my edge bevels tend to be fairly wide, making it pretty easy to feel when you are on the correct angle.
Probably the most significant thing I realized was that stropping compounds applied to flexible substrates appear to leave an apex finish much finer than you would expect based on the grit rating. It suddenly occurred to me that it was possible that most of the complaints made about the dangers of excessive stropping could be explained by the use of very fine grit stropping compounds which, after a large number of passes on the strop, were eliminating all the slicing aggression of the apex and leaving a straight-razor like finish.
I tested this idea by moving to coarser and coarser compounds, from 4 to 6 to 8 and ultimately 16 micron, and what I found is that it is possible to generate extreme levels of push-cutting sharpness even with seemingly very coarse stropping compound, and that coarser compounds will not eliminate the slicing aggression of the apex, even after hundreds of passes on the strop.
Some pictures as an example, taken with my cheap 50x optical 5x digital zoom microscope at max zoom:
Spyderco HAP40 Endura with the edge bevel shaped at 1,000 grit (Note; I'd previously been re-flattening the edge bevels on a 240x stone hance the fairly ragged edge-bevel):
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Refined to 6,000x. No attempt was made to arrive at a totally clean and straight apex to highlight the effect in subsequent images.
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HAP40 Endura after 10pps on leather bench strop pasted with 16.0 micron CBN emulsion:
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HAP40 Endura after 30pps on leather bench strop pasted with 16.0 micron CBN emulsion:
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As can be seen, the 16.0 micron CBN emulsion on leather forms a clean, burr free apex, and leaves a scratch pattern that looks nothing like what I would have expected from a 16 micron abrasive.
Also unexpected was the extreme level of push-cutting sharpness achievable in this manner. This apex will trivially push-cut newsprint at 90/90/90 across the grain at some distance from the point of hold while still retaining enough slicing aggression to be able to cleanly slice through a whole sheet of paper towel held on both sides of the cut.
I really suspect I could get an apex that would push-cut newsprint at 90/90/90 across the grain off a leather strop pasted with a 20 or 30 micron abrasive, honestly.
Furthermore, I've been EDCing some of my knives sharpened this way and using them as I would when they had been apexed on Spyderco F rods, and the high sharpness edge retention seems subjectively to be noticeably better than what I was getting previously using the ceramic rods. I eventually plan to test that, but for now I feel confident in saying that the high-sharpness edge-retention is certainly not worse than what I am used to.
The ease of touching up the micro-bevel also seems to at least be comparable to what I was getting from using my Spyderco F rods for this purpose, notably, even after a week or two of repeated touch-ups after use, no loss of slicing aggression was noticed. As far as I can tell, I have been totally unable to "kill and edge" this way.
This has all been quite interesting and fun to explore, but it really baffles me that I can find little to no information or exploration of this subject online. It seems as though very few people have seriously explored what levels of push-cutting sharpness are obtainable off of coarse stropping compounds.
A while back, my interest in re-exploring the topic was piqued by some SEM images produced by the Science of Sharp blog in this post about burr removal. In particular, the idea of Mothers Mag & Aluminium polish on a hanging denim strop producing the pictured apex interested me.
Subsequently, I have tried a variety of stropping compounds and substrates in trying to see what results I could obtain. I've tried Mothers Mag & Aluminium Polish, 0.25, 1.0, 2.0 and 6.0 micron diamond pastes, and 8.0 and 16.0 micron CBN emulsions.
These compounds have been tried on hanging denim, hanging leather, and block mounted leather strops.
My goal was to explore whether pasted strops could make a viable alternative for creating and maintaining micro-bevels on my EDC knives, which I had previously been doing with a Spyderco Sharpmaker with the M or F rods.
In each case, I cut off the previous edge on the knife, and shaped the edge-bevel using a three-step sharpening method approach starting with my Sigma Power Select II 1,000x stone and then refined the edge on my SPS-II 6,000x stone prior to stropping.
I found that I had a much easier time precisely getting the angle I wanted and the contact area I wanted using block backed leather strops. This surprised me, as I had assumed the hanging strops would be easier to use, but I found it very difficult to get any consistency with the hanging strops. Conversely, I've found the leather bench strops fairly easy to use, but I probably have an advantage with that because my edge bevels tend to be fairly wide, making it pretty easy to feel when you are on the correct angle.
Probably the most significant thing I realized was that stropping compounds applied to flexible substrates appear to leave an apex finish much finer than you would expect based on the grit rating. It suddenly occurred to me that it was possible that most of the complaints made about the dangers of excessive stropping could be explained by the use of very fine grit stropping compounds which, after a large number of passes on the strop, were eliminating all the slicing aggression of the apex and leaving a straight-razor like finish.
I tested this idea by moving to coarser and coarser compounds, from 4 to 6 to 8 and ultimately 16 micron, and what I found is that it is possible to generate extreme levels of push-cutting sharpness even with seemingly very coarse stropping compound, and that coarser compounds will not eliminate the slicing aggression of the apex, even after hundreds of passes on the strop.
Some pictures as an example, taken with my cheap 50x optical 5x digital zoom microscope at max zoom:
Spyderco HAP40 Endura with the edge bevel shaped at 1,000 grit (Note; I'd previously been re-flattening the edge bevels on a 240x stone hance the fairly ragged edge-bevel):
Refined to 6,000x. No attempt was made to arrive at a totally clean and straight apex to highlight the effect in subsequent images.
HAP40 Endura after 10pps on leather bench strop pasted with 16.0 micron CBN emulsion:
HAP40 Endura after 30pps on leather bench strop pasted with 16.0 micron CBN emulsion:
As can be seen, the 16.0 micron CBN emulsion on leather forms a clean, burr free apex, and leaves a scratch pattern that looks nothing like what I would have expected from a 16 micron abrasive.
Also unexpected was the extreme level of push-cutting sharpness achievable in this manner. This apex will trivially push-cut newsprint at 90/90/90 across the grain at some distance from the point of hold while still retaining enough slicing aggression to be able to cleanly slice through a whole sheet of paper towel held on both sides of the cut.
I really suspect I could get an apex that would push-cut newsprint at 90/90/90 across the grain off a leather strop pasted with a 20 or 30 micron abrasive, honestly.
Furthermore, I've been EDCing some of my knives sharpened this way and using them as I would when they had been apexed on Spyderco F rods, and the high sharpness edge retention seems subjectively to be noticeably better than what I was getting previously using the ceramic rods. I eventually plan to test that, but for now I feel confident in saying that the high-sharpness edge-retention is certainly not worse than what I am used to.
The ease of touching up the micro-bevel also seems to at least be comparable to what I was getting from using my Spyderco F rods for this purpose, notably, even after a week or two of repeated touch-ups after use, no loss of slicing aggression was noticed. As far as I can tell, I have been totally unable to "kill and edge" this way.
This has all been quite interesting and fun to explore, but it really baffles me that I can find little to no information or exploration of this subject online. It seems as though very few people have seriously explored what levels of push-cutting sharpness are obtainable off of coarse stropping compounds.
