I circled some spots on the images so we'd have some things to compare. Here is the blade after the 50# diamond plates:



and here it is after 5 strokes with the .75um strops:



In the green circle and to some extent in the fuchsia ellipses, you can clearly see signs of abrasion from the .75um CBN. In the red and aqua circles, it looks like the metal has been dragged around a little bit. It has an almost liquid appearance as though it had flowed.

I don't have the background to speak to this, but I wonder, as Phil has voiced, if there is enough local pressure to move these delicate structures and deform them. I measured the little elongated structure in the red circle (after being stropped) to be 1.6um, which is very tiny. How many pounds per square inch would be needed to get something that small to flow? Even more to the point, can the leather grab surface molecules and shift them, like buttering bread? The next round of testing should be interesting. I'll try it with alcohol moistened strops with no abrasive other than the grain of the leather. Once the plain paste comes in, I'll try to duplicate the level of stiction I'm getting and test that way too, maybe on kangaroo.

I never thought I'd see "fuchsia" in a sharpening forum....

Maybe someone who's a member of an engineering forum could post these pics and solicit some responses there?

I also had another thought along with trying plain leather would be to try balsa plain and/or loaded... see what that shows.

cbwx34 wrote:


Me either, but it seems to work well.

Okay, more photos raising more questions. First the 50# sample followed by the strops with no abrasives:



now plain cow leather, moistened with alcohol:



and then plain kangaroo leather, moistened with alcohol:



Next I'll post some pictures after using strops with some abrasives.

First off is .125 CBN on Nano-Cloth:



now 3.5um Diamond on Balsa, moistened with alcohol - 5 strokes:



and then 3.5um Diamond on Leather, moistened with alcohol - 5 strokes:



Clearly there is plenty of abrasion going on with the 3.5um diamonds.

There was absolutely no 'stiction' going on with the plain leather. It was just gliding smoothly over the metal. I think I'm somewhat stuck here until the plain paste arrives and I can do some true apples to apples comparisons. I'm thinking of .5um diamond paste on leather vs. .5um diamond on balsa vs. plain paste on leather vs. plain paste on balsa. .5um is visible in the scope but shouldn't be so abrasive as to immediately obliterate the sample like the 3.5um does.

For grins, I completed 60 strokes with the 3.5um Diamond on Cow Leather:



The one thing I have learned is how to get back to the same spot on the sample in the microscope's field of view

Hey Clay,
Interesting ..I was going to try to circle those aqua areas myself.
That small feature looks like it may have been a thin flap in the 50 grit photo, cut by the diamonds. Being as this as it is, it looks like it got sort of folded over and moved a bit and flattened. This might not take much force. After all the piece is probably not as thick as a piece of aluminum foil.

One thing to remember as well. There is a grit distribution in any compound. There are probably abrasive particles in the 0.75 micron compound that range from at least 0.25 to maybe 1.5 microns. These varying sized grits could also be contributing to the smoothing at a level finer than what we can resolve even at this magnification.

Some of the other features definitely look like perhaps they may have been changed by abrasion, albeit very fine abrasion.

The fushia area on the second photo looks like metal has been removed... and smoothed. Perhaps again, abrasion.

I found it very interesting that the blank leather strops had virtually no effect at all. The Kangaroo seemed to make more of a change. This runs a bit counter to what we have seen where "roo strops seem to not contribute to the process much at all when used with abrasives. ???

This is very interesting. I wish I had more experience at interpreting features and their causes at this level of magnification.

Phil

wickededge wrote:

wickededge wrote:


This is a very interesting result. I already knew that loaded strops (both leather and balsa) can be quite effective, but I also thought that plain leather would have some effect. But apparently leather does very little by itself. This makes me wonder why stropping on plain leather is often seen as effective, particularly when doing straight razors. Is it only a matter of straightening the edge?

I recall a blog by Michiel (on belgiansharpening) where he showed that plain horse leather does have an abrasive effect. If I recall it correctly, he explained that this is due to the silicates embedded in the horse leather. And I think that some of your pictures at 200x also showed that plain leather had some abrasive effect (but maybe this was distortion due to the lower magnification).

Wow, what a fascinating thread, I've only caught up reading recently.

Clay, those pictures are awesome!

I don't have too much to add to the speculation, but I have some information that might be relevant.

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(1) Abrasion is a very complicated subject. There are entire engineering books about just abrasion, and then separate entire engineering books about polishing and lapping. When abrasion is not desirable, it's called lubrication. And lubrication has entire books written about it. Not to mention, friction is poorly understood, even today, despite centuries of scientific study. My thought is to speculate, make theories, and do tests, but then to keep in mind that such things can be insanely complicated which means we could easily be wrong.

btw, I hope to eventually read two engineering books, one on abrasion, and another on polishing and lapping.

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(2) In Prof. John Verhoeven's technical report, _Experiments in Knife Sharpening_, he has several scanning electron microscope (SEM) images of knive edges before and after stropping. He also tried stropping with and without compound. Verhoven's pictures are the highest resolution and most detailed images of knife edges I have seen so far. It may be worth reviewing his work, and comparing notes with Clay's studies.
www-archive.mse.iastate.edu/fileadmin/ww...even/KnifeShExps.pdf

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(3) Just a reminder of length scales relevant to knife sharpeners:

The two most important length scales are:
0.4 microns, which is the sharpness of a modern razor
0.2 microns, which is the resolution limit of optical microscopes. btw, this resolution limit is from physics of light, which diffracts slightly as it goes through the microscope objective. That slight diffraction causes blurring. Only very high-quality optical microscopes can approach this resolution limit. I would not expect any "consumer" microscope to achieve a resolution of 0.2 microns, but a high-quality laboratory microscope probably can get close.

180 - 7 Microns: Diameter of human hair. en.wikipedia.org/wiki/Hair
100 Microns: Approximate thickness of paper (copier paper of weight 24 lbs; 500 sheets is about 2 inches thick).
16 Microns: Thickness of household aluminum foil. en.wikipedia.org/wiki/Aluminum_foil
25.4 Microns: = 0.001 inches (1.0 mil). Standard resolution for an imperial caliper.
2.54 Microns: = 0.0001 inches (0.1 mil). Standard resolution for an imperial micrometer.
0.75 - 0.38 Microns: Wavelength of visible light. en.wikipedia.org/wiki/Visible_light
0.4 Microns: Sharpness of a modern razor blade. www-archive.mse.iastate.edu/fileadmin/ww...even/KnifeShExps.pdf
0.2 Microns: Resolution limit of optical microscopes. www.microscopyu.com/articles/optics/objectiveproperties.html
0.05 Microns: Sharpness of diamond coated razor blades. www.technologyreview.com/computing/25988/
0.005 Microns: Sharpness of a diamond microtome knife. www.tedpella.com/diamond_html/diamondk.htm
0.003 Microns: Sharpness of concoidally fractured obsidian. en.wikipedia.org/wiki/Obsidian
0.003 microns: Distance between a hard drive head and the spinning platter. en.wikipedia.org/wiki/Disk_read-and-write_head
0.00034 Microns: Van Der Waals diameter of a single carbon atom. en.wikipedia.org/wiki/Van_Der_Waals_Radius

The needles used in scanning-tunnelling-electron-microscopes (STEM) and atomic-force-microscopes (AFM) are so sharp they literally have a single atom at their tips.
Also, x-ray telescope mirrors are atomically smooth. www.mpe.mpg.de/xray/wave/technologies/mirror.php

This is also fairly interesting when combined with Komitadjie's Grand Unified Grit Chart, which is an approximate conversion between sharpening stone grits and microns. The graph below is made by Mr. Wizard who used the data compiled by Komitadjie.
www.knifeforums.com/forums/showtopic.php?tid/904090/tp/7/


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(4) Some rough definitions, as I understand them:
Grinding: Abrasive particles bound in a hard matrix.
Lapping: Loose abrasives which are applied with a soft backing (like leather). The particles abrade as the roll around, and also as they embed into the softer material.
Polishing: Same as lapping, but done with much finer abrasive and used to get a mirror finish.
Burnishing: Mainly "smearing" of the surface with only minor abrasion (removal of material).

en.wikipedia.org/wiki/Abrasive_machining
en.wikipedia.org/wiki/Burnishing_(metalworking)

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(5) So far, I think that stropping is mainly an abrasive process. Abrasion always involves some burnishing, since dragging particles across the surface can push material around without necessarily removing material. During abrasion, probably the dominant process is removing material, but some incidental burnishing is likely or even common.

Like PhilipPasteur, I'm not yet convinced that burnishing is the dominant effect in stropping. But I'm far from sure either way. Consider the following example: water is very soft. But rushing water can exert tremendous forces. Similarly, if we have a miroscopic "peak" of metal, then what happens as leather "rushes" over it during rubbing? Especially if the rubber has abrasives embedded in it. Well... I have no idea. But it would be interesting to find out!

Not related, but I'm reminded of abrasive water-jet cutting which is used to cut stone and steel. The water jet is typically a mixture of water and garnet abrasive, and is travelling at a velocity of up to 3 to 4 times the speed of sound.
www.flowwaterjet.com/en/waterjet-technology/hyperpressure.aspx

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Okay, that's all I have for now.

Sincerely,
--Lagrangian