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.
Re: A Reconsideration of Stropping
April 04, 2016 04:12PM
Steel_Drake-
Interesting topic. I have been wondering about this topic also. I think that as long as you strop in moderation, and properly sharpen the knife, ie form a good apex, it definitely can help in push cutting sharpness and edge apex refinement. The two things I wonder about is how it could affect edge retention, either by helping to have a cleaner apex or micro-convexing, and how much of an increase in push cutting ability is gained. I have found that if the blade geometry is thin and the edge geometry acute, slicing aggression can be retained to a functional degree. A good example if this is a utility/razor blade. I basically would want to imitate the out-of-box Sypderco edges that topped Cliff's sharpness measurements in slicing and push cutting, and if by hand sharpening achieve even a better edge, I would be very happy.

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Re: A Reconsideration of Stropping
April 04, 2016 04:26PM
Quote
jasonstone20
I have found that if the blade geometry is thin and the edge geometry acute, slicing aggression can be retained to a functional degree.

This is a good point, and one I forgot to mention. All of my knives have edge bevel angles in the 7-10 degree per side range and all are 0.015" thick at 1/32" back from the apex or less, thus they are all fairly thin and have fairly low edge bevel angles.

I am also looking for where I can source a ~30 micron CBN or Diamond compound to try it, I'm curious to see how coarse I can go before the ability to push-cut newsprint across the grain next to the point of hold at 90/90/90 is lost.
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"winking smiley ~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.
Re: A Reconsideration of Stropping
April 05, 2016 09:02PM
Steel_Drake,
Nice! It helps a lot to see what's going on with the edge apex.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: A Reconsideration of Stropping
April 06, 2016 12:54AM
Might this be due to the fact that the CBN emulsion is simply more abrasive than the usual green chromium oxide paste?


Either way, that is damn impressive.

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Edited 1 time(s). Last edit at 04/06/2016 12:55AM by Bugout Bill.
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.
Re: A Reconsideration of Stropping
April 06, 2016 01:51AM
Quote
Bugout Bill
Might this be due to the fact that the CBN emulsion is simply more abrasive than the usual green chromium oxide paste?


Either way, that is damn impressive.

Bill,

I think that plays a roll, both in that CBN or Diamond should be able to cut any steel type effectively and should be hard enough to avoid breaking down into smaller particles in use.

Since it seems that larger particle sizes (above ~5 microns) are important to avoid the potential of eliminating all slicing aggression from the apex, it stands to reason that compounds that can break down into smaller particles or which cut less effectively on some steels should be avoided.

Fundamentally, I think the issue is that very few people seem to have tried larger particle size compounds for this application, there is actually very little discussion out there that I could find of using 5+ micron stropping compounds to finish on, without following with finer compounds.
Re: A Reconsideration of Stropping
April 06, 2016 02:20AM
Steel_Drake,
That's what I was commenting on, the Naniwa 2k Green Brick really puts a nice edge on. I have been thinking about this topic for sometime, and re-read Dr. Verhovens paper on sharpening, where 1m Diamond compound produced a slightly smaller edge width (EW), 0.03m vs 0.5m CrO compound, with an EW of 0.04m. Science of Sharp (Todd) has also done some eexcellent imaging exploring this topic also, and I see you quoted the link to his work.

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Re: A Reconsideration of Stropping
April 06, 2016 02:30AM
Quote
jasonstone20
Steel_Drake,
That's what I was commenting on, the Naniwa 2k Green Brick really puts a nice edge on. I have been thinking about this topic for sometime, and re-read Dr. Verhovens paper on sharpening, where 1m Diamond compound produced a slightly smaller edge width (EW), 0.03m vs 0.5m CrO compound, with an EW of 0.04m. Science of Sharp (Todd) has also done some eexcellent imaging exploring this topic also, and I see you quoted the link to his work.

Ironically, consiseing how many waterstones i've bought since I got one, the Green Brick is fairly close to ideal as a finisher for this method before moving to the strop because it cuts fairly quickly while leaving a fairly crisp apex line.

I'm currently using my Naniwa Chosera 400 to shape edge bevels, the Aotoshi to get a fairly clean apex line, and then setring the apex on the strop.

And it was actually Todd at Science of Sharp that originally inspired this exploration with his SEM images of stropped edges.
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.
Re: A Reconsideration of Stropping
April 07, 2016 02:03AM
Where did you source the CBN from, Steel Drake?

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Bill22252 on YouTube. "See you space cowboy"

Resident Emerson Fanboi

Folding knives are fun, fixed blades are important.
Re: A Reconsideration of Stropping
April 07, 2016 02:27AM
Quote
Bugout Bill
Where did you source the CBN from, Steel Drake?

The CBN emulsions I purchased from here at Jende Industries.

I am in the process of ordering 20, 28 and 40 micron diamond polishing compounds to try, as I found a seller for them located in Canuckistan.
Re: A Reconsideration of Stropping
April 07, 2016 02:38AM
Steel Drake: Color me intrigued. I might need to buy me a strop then.

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Folding knives are fun, fixed blades are important.
Re: A Reconsideration of Stropping
April 07, 2016 11:19AM
Steel_Drake-
How many passes per side are you using?

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
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Re: A Reconsideration of Stropping
April 07, 2016 12:26PM
Quote
Bugout Bill
Steel Drake: Color me intrigued. I might need to buy me a strop then.

Bill,

KENT diamond polishing grits should work just as well (that's what I've ordered for 20, 28, and 40 grit sizes) and may be available cheaper to you than the CBN emulsions.

Quote
jasonstone20
Steel_Drake-
How many passes per side are you using?

I'm using 20-30 passes per side because it seems to take that many to fully create a convex micro-bevel (this is shown in the initial set of images). Passes are made alternating sides and scratch patterns, last ~5 pps are made using short strokes for burr minimization purposes.
Re: A Reconsideration of Stropping
April 07, 2016 10:52PM
SD-
Thank you.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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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.
Re: A Reconsideration of Stropping
April 14, 2016 01:59AM
SD-
I think the cleaner the apex, you mmight get better the edge retention and performance of the blade. Not sure however, just from what I have seen, read, and other work.

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: A Reconsideration of Stropping
April 14, 2016 11:08PM
I decided to make a short video introducing what I've been working on.

[www.youtube.com]



Edited 1 time(s). Last edit at 04/14/2016 11:10PM by Steel_Drake.
Re: A Reconsideration of Stropping
April 15, 2016 12:15AM
SD - Thanks for sharing all this work and the video. Certainly looks like something interesting to experiment with on a daily use edge. I usually finish on the SPSII 1000x and then micro bevel on Spyderco ceramics but I do have the SPSII 3000x as well. Would that be close enough in your estimation?

What was your final opinion on the Kent diamond lapping compounds? They are easy to get from Amazon in Canada. A set of the 7,10,14,20,28 and 40 are $39. Or would you suggest just a couple of those?
Re: A Reconsideration of Stropping
April 15, 2016 12:26AM
Chris,

The SPS-II 3000x should be fine enough for this type of apex finish, I prefer the 6000x only because it yields a smoother apex line which in turn yields slightly higher push-cutting sharpness once apexed, and SPS-II stones cut so fast that there is little added time for jumping straight to 6000x from 1000x.

The Kent diamond lapping compounds certainly work, I would just probably try the 10 or 14 micron to obtain similar results to the 16 micron CBN emulsion, and 20 if I wanted significantly more slicing aggression in exchange for a small reduction in push cutting sharpness.
Re: A Reconsideration of Stropping
April 15, 2016 12:39AM
S_D,
Nice work!
I thought of two questions while watching the video.
1. Have too tried the old timer trick of using reclaimed stone slurry on your strop?
2. Have you noticed a difference in performance vs your 13k SPS II edge, apexed on the Sharpmaker Spyderco UF rod?
Thank you!

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: A Reconsideration of Stropping
April 15, 2016 12:43AM
Jason,

I haven't tried that yet, though I may end up trying it at some point. For now, I've got some even coarser CBN emulsions on order to try (30, 45 and 80 micron).

As for comparing the performance of this apex finish to what I was using before, this finish has been giving significantly better initial push-cutting sharpness, slightly better slicing aggression, and significantly better high-sharpness edge retention. As I noted in the video, I was pretty amazed at still being able to push-cut newsprint at 90 degrees across the grain after about a dozen slices into corrugated cardboard.
Re: A Reconsideration of Stropping
April 15, 2016 12:54AM
Steel_Drake-
I have gotten similar results using Flexcut Gold compound and Knife Strop, along with one I built using a paint stir stick and an old belt with Mothers Mag Polish and Enkay Green. Same results with the strops I made for my EP Clone. I only use my hanging strop for razors, I find a hard backed one works best for knives. Not really sure why. I also use MetalGlo, which works like the Mothers.

PS-I also use HS5's CrOx Stropping Spray

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Edited 1 time(s). Last edit at 04/15/2016 01:02AM by jasonstone20.
Re: A Reconsideration of Stropping
April 15, 2016 01:11AM
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
Interesting ... how much slicing agression is there on the paper towel before stropping?

____
Thanks
I don't mow smiling smiley
Re: A Reconsideration of Stropping
April 29, 2016 04:29AM
Have you tried taking something like a Norton India edge and then stropping it?

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Bill22252 on YouTube. "See you space cowboy"

Resident Emerson Fanboi

Folding knives are fun, fixed blades are important.
Re: A Reconsideration of Stropping
April 29, 2016 06:07PM
SD, Bill-
I was wondering a similar thing. What if you put a stone or diamond plate on a soft material, ie mousepad, to induce the micro-convexity? And how much of a difference does the micro-convex help retain high sharpness? Does it hurt or help edge retention of a slice? On a push?

"I am still discussing issues of steels and performance at this stage." -- Cliff Stamp, May his memory be a blessing
"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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Re: A Reconsideration of Stropping
April 29, 2016 07:27PM
ShaperAndMower,

The slicing aggression straight of an SPS-II 6000x is similar to that off the 20 micron diamond paste, has no problem slicing the paper towel, but doesn't make as smooth a slice as the 16 micron CBN does.

Bill,

I haven't tried that yet I like to start with a fairly straight apex line before applying the convex microbevel and a Norton India fine would leave a fairly uneven apex line. I do know that you can achieve most/all of the effect going from an SPS-II 1000x directly to a strop pasted with 16 micron CBN emulsion.

Jason,

My initial guess as to why these convex microbevels on coarse particulate abrasives are appearing to have better high sharpness edge retention is twofold:

1) Subjectively, it appears that the convex microbevels induced using coarse particulate abrasives are getting much of their push cutting sharpness from having very thin apexes, which appears to be offsetting the micro-teeth being created at the apex. This would explain why even 30-45 micron particulate abrasives are able to create micro-bevels which will still push-cut newsprint across the grain even while having quite toothy apexes.

2) The geometry of the convex vs. a v-shaped microbevel might lead to the convex one being thinner at the actual apex, but thicker just behind it, leaving a stronger apex.

These are largely suppositions and should be taken as such, mind you.
Re: A Reconsideration of Stropping
May 01, 2016 08:05PM
I just tried the Mothers/Denim combination, and with just 3-4 pps, I had a nice micro-convexed microbevel. I will see if I noticed any difference in high-edge holding. I sometimes strop 3-4 pps when sharpening, but usually I don't have to using Cliff's 3-Step/Plateau Method, or W. Goddards method, I only see a small improvement in the edge, so this should be interesting. I might give this treatment to a kitchen knife, which will see more use than my desk knife, which I just applied the MC MB to.

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"Life is GOOD", -- Stefan_Wolf, May His Memory Be A Blessing
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