A Reconsideration of Stropping
Posted by Steel_Drake
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A Reconsideration of Stropping April 04, 2016 03:36PM |
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):
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.
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.
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Re: A Reconsideration of Stropping April 05, 2016 04:19PM |
I forgot to mention that I always cross my scratch patterns, both on benchstones and on the strop, which leaves a finer finish at any given grit than you would get otherwise. I will try and remember to take some images where I don't cross scratch patterns for this thread.
Now, a few more USB microscope images of knives stropped on 16 micron CBN emulsion on a leather bench-strop:
(Note: These were taken at 50x optical magnification and WITHOUT digital zoom, unlike the images above in my original post.)
VG-10 Spyderco Junior with the edge bevel polished on a Naniwa Aotoshi ~2k stone and then stropped on 16 micron CBN emulsion on a bench-strop using ~20-30 alternating edge-trailing passes per side:
Carbon Morakniv Companion MG with the edge bevel polished on a Naniwa Junpaku (aka "Snow White"
~8k and then stropped on 16 micron CBN emulsion on a bench-strop using ~20-30 alternating edge-trailing passes per side:.
Finally, my latest Calton Cutlery necker in 1095 (it is one of the no-choil models). The edge bevel was finished on a Naniwa Aotoshi ~2k stone and then stropped on 16 micron CBN emulsion on a bench-strop using ~20-30 alternating edge-trailing passes per side.
The apex obtained on the Calton 1095 using this method is the highest push-cutting sharpness I've ever seen, and yet the apex retains sufficient slicing aggression to trivially cleanly slice folded over paper towel.
Now, a few more USB microscope images of knives stropped on 16 micron CBN emulsion on a leather bench-strop:
(Note: These were taken at 50x optical magnification and WITHOUT digital zoom, unlike the images above in my original post.)
VG-10 Spyderco Junior with the edge bevel polished on a Naniwa Aotoshi ~2k stone and then stropped on 16 micron CBN emulsion on a bench-strop using ~20-30 alternating edge-trailing passes per side:
Carbon Morakniv Companion MG with the edge bevel polished on a Naniwa Junpaku (aka "Snow White"
~8k and then stropped on 16 micron CBN emulsion on a bench-strop using ~20-30 alternating edge-trailing passes per side:.
Finally, my latest Calton Cutlery necker in 1095 (it is one of the no-choil models). The edge bevel was finished on a Naniwa Aotoshi ~2k stone and then stropped on 16 micron CBN emulsion on a bench-strop using ~20-30 alternating edge-trailing passes per side.
The apex obtained on the Calton 1095 using this method is the highest push-cutting sharpness I've ever seen, and yet the apex retains sufficient slicing aggression to trivially cleanly slice folded over paper towel.
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Re: A Reconsideration of Stropping April 06, 2016 01:37AM |
Quote
jasonstone20
Steel_Drake,
Nice! It helps a lot to see what's going on with the edge apex.
Jason,
One of the main points I'm trying to show with the pictures is that the 16 micron CBN emulsion on leather leaves a finish quite obviously considerably finer than the 1,000 grit rating of the emulsion would suggest.
Another example from today:
ZDP-189 Spyderco Caly 3.5 with the edge bevel finished on a Naniwa Aotoshi ~2k stone:
ZDP-189 Spyderco Caly 3.5 after ~20-30 alternating pps edge-trailing on a leather bench strop pasted with 16 micron CBN emulsion:
As you can see, the 16 micron CBN on leather leaves a coarser scratch pattern than the Naniwa Aotoshi does, but certainly nothing like the scratch pattern you would expect from a ~1,000 grit stone.
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Re: A Reconsideration of Stropping April 07, 2016 01:01AM |
I believe that crossing scratch patterns make minimizing burr formation significantly easier when using this technique, as I've discovered when trying to get a burr free apex without crossing scratch patterns. It can be done, but requires a bit more patience and finesse.
Crossing scratch patterns and using short passes on the finishing strokes makes burr minimization fairly trivial.
I've also been trying a bench strop constructed by simply taping two strips of leather (one on top of the other) to a strip of wood:
The idea was to create a bench strop with a more pliable substrate to induce more of a convex in the micro-bevel to see what effect (if any) it would have on initial sharpness and high-sharpness edge retention. I came up with this in response to noticing that gluing a piece of leather to another block of wood has significantly reduced the pliability of the leather, and was thus inducing less of a convex than I'd intended.
So far, at first blush it appears to be having the desired effect.
Crossing scratch patterns and using short passes on the finishing strokes makes burr minimization fairly trivial.
I've also been trying a bench strop constructed by simply taping two strips of leather (one on top of the other) to a strip of wood:
The idea was to create a bench strop with a more pliable substrate to induce more of a convex in the micro-bevel to see what effect (if any) it would have on initial sharpness and high-sharpness edge retention. I came up with this in response to noticing that gluing a piece of leather to another block of wood has significantly reduced the pliability of the leather, and was thus inducing less of a convex than I'd intended.
So far, at first blush it appears to be having the desired effect.
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Re: A Reconsideration of Stropping April 14, 2016 01:19AM |
I've gotten my hands on some 20, 28 and 40 micron diamond paste made by KENT.
NOTE: Image taken at maximum optical (50x) and digital (5x) magnification of my USB microscope. 16 micron CBN finish on right was applied over top of previous 20 micron diamond finish on left.
Even the 20 micron diamond paste appears to have a significantly coarser effective grit than the 16 micron CBN emulsion on leather. I suspect that the heavy grease of the diamond paste is causing more of the grit to remain on top of rather than embedded in it, compared to the evaporating water soluble emulsion the CBN is suspended in. Additionally, I suspect the grading to be much tighter on the CBN emulsion.
Also, the high sharpness edge retention of a 16 micron CBN on leather apex finish appears to be extremely high. On several separate occasions with different knives I've found that edges have retained the ability to push cut newsprint at 90/90/90 across the grain after multiple cuts were made into corrugated cardboard, whereas previously (using ceramic rod microbevels) that level of push cutting sharpness was lost after 1-2 cuts into corrugated cardboard.
Today, out of curiosity, I wanted to see just how many slices of corrugated cardboard it would take before a 16 micron CBN on leather apex lost the ability to push cut newsprint at 90/90/90 across the grain.
The answer turned out to be after about ~15 slices of ~7" each:
Mind you, at this point there were still parts of the apex that would still do 90/90/90 across the grain push cuts, but they were few and far between. After 10 cuts it had still been doing them easily. Compared to the high-sharpness edge retention I was getting before, this honestly appears to be a drastic, noticeable improvement.
NOTE: Image taken at maximum optical (50x) and digital (5x) magnification of my USB microscope. 16 micron CBN finish on right was applied over top of previous 20 micron diamond finish on left.
Even the 20 micron diamond paste appears to have a significantly coarser effective grit than the 16 micron CBN emulsion on leather. I suspect that the heavy grease of the diamond paste is causing more of the grit to remain on top of rather than embedded in it, compared to the evaporating water soluble emulsion the CBN is suspended in. Additionally, I suspect the grading to be much tighter on the CBN emulsion.
Also, the high sharpness edge retention of a 16 micron CBN on leather apex finish appears to be extremely high. On several separate occasions with different knives I've found that edges have retained the ability to push cut newsprint at 90/90/90 across the grain after multiple cuts were made into corrugated cardboard, whereas previously (using ceramic rod microbevels) that level of push cutting sharpness was lost after 1-2 cuts into corrugated cardboard.
Today, out of curiosity, I wanted to see just how many slices of corrugated cardboard it would take before a 16 micron CBN on leather apex lost the ability to push cut newsprint at 90/90/90 across the grain.
The answer turned out to be after about ~15 slices of ~7" each:
Mind you, at this point there were still parts of the apex that would still do 90/90/90 across the grain push cuts, but they were few and far between. After 10 cuts it had still been doing them easily. Compared to the high-sharpness edge retention I was getting before, this honestly appears to be a drastic, noticeable improvement.
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Re: A Reconsideration of Stropping April 15, 2016 01:11AM |
Interesting ... how much slicing agression is there on the paper towel before stropping?Quote
Steel_Drake
I decided to make a short video introducing what I've been working on.
A Brief Introduction to Coarse Particulate Abrasive Stropping - YouTube
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