A theory of how the WE diamond pastes work

[wickededge]

Okay 🙂 I’ll try to get some better pictures of it. In that one section the metal is smeared across those scratches, filling in the valley. It may be easier to show if I start with a slightly rougher surface. Stuff to work on…

-Clay

[wickededge]

Here are a couple more images of a knife edge at 2000x. In order to make a fair comparison, it’s essential to capture the same features in each image and at high magnification, it’s hard to find your way back to a tiny feature after you’ve removed the sample. What I did to solve the problem was to make a nick in the blade. A laser or engraving machine would have been great, but I had to make do with what I had – another sharp knife! After creating the nick, I sharpened the knife with the 400# diamond plates because I wanted fairly deep grooves with tall ridges. I completed 20 strokes per side, perpendicular to the edge. I then made one stroke parallel to the edge. I knew I’d be able to find the edge of the nick in the microscope and then all I had to do was locate a unique intersection of scratches:

I removed the sample and cleaned it well, the completed 5 strokes per side with firm pressure using .75um CBN on cow leather. I had not trouble locating the same intersection again and getting another picture:

It’s hard to believe that only 5 strokes makes such a huge difference. I originally did my testing with quite a few strokes and found to my chagrin that I’d obliterated almost all the scratches from the stone.

Attachments:

• 400-Grit.jpg
• 75-CBN-after-400-Grit.jpg

-Clay

[wickededge]

I decided to repeat the process with the 100# diamond plates:

Attachments:

• 100-Grit.jpg
• 75-CBN-after-100-Grit.jpg

-Clay

[wickededge]

I’m going to try again with the 50# diamond plates because I want to see if the metal is actual being moved, not just abraded. I’ll go with coarser strops as well so we can see the abrasion from those clearly.

-Clay

[Mark76]

Wow, that’s great! These photographs show very well what how burnishing works!

Molecule Polishing: my blog about sharpening with the Wicked Edge

[wickededge]

Same experiment, this time with the 50# diamond plates. Again, only 5 strokes with the strops.

Attachments:

• 50-Grit.jpg
• 75-CBN-after-50-Grit.jpg

-Clay

[Mark76]

Would be really cool, Clay, if you could compare the burnishing (and abrasion) caused by the .75 CBN (which seems huge) to that caused by plain strops and by strops loaded with a WE paste.

Molecule Polishing: my blog about sharpening with the Wicked Edge

[wickededge]

Would be really cool, Clay, if you could compare the burnishing (and abrasion) caused by the .75 CBN (which seems huge) to that caused by plain strops and by strops loaded with a WE paste.

Hopefully I can do that today. I’m testing some arms from our machine shop and have to give feedback, so that will have to come first…

-Clay

[cbwx34]

So, does this mean that when stropping and the edge seems to “dull” a bit, we’re not necessarily “rounding” the edge, but rather pushing metal up on top of it?

[wickededge]

So, does this mean that when stropping and the edge seems to “dull” a bit, we’re not necessarily “rounding” the edge, but rather pushing metal up on top of it?

That is a really good question! It’s conceivable that we are pushing metal up behind the edge, but I’m not sure how much we’re really talking about. I’d like to do some good cross section studies and find out.

-Clay

[Phil Pasteur]

Hey Clay,

I don’t claim to be an expert, but everytime this subject comes up I go out and do more research on burnishing. In every case that I have come across burnishing is done with a harder material on a softer material. The idea is that you have to exceed the yeild strength of the softer material to get it to flow. There are some among us, even in the absence of hard evidence (not talking you Clay) that have accepted without question that leather can burnish steel. Clay, you have a theory, and you are out to find evidence to support that. This is entirely different.

I still have a hard time understanding how leather rubbed against hardened steel can exceed the yeild strength of the steel and make it flow, local pressures and stiction notwithstanding.
I did come accross an article today that stated, and I paraphrase, that in grinding (really what we do whe we sharpen) there will usually be some small level of burnishing because of the orientation of the abrasives and the fact that they are not all as sharp as the rest. These duller abrasives are being dragged accross the subject material and instead of cutting, they burnish. This effect can be considered to be minimal in the entire process of abrading the subject material. I can more easily see this as being the cause of what you are seeing at 2500X.

Keep in mind, I started my education…a long, long time ago, with a degree in mechanical engineering… the material science part of this just (from what I remember) isn’t making sense (yet). This is why I am looking for different explanations.

I noticed in your first pic of the edge at 50 grit that there are some places where the metal looks like it has been burnished in small areas as evidenced by the smoothing of some areas. I am going to see if I can copy the pics and circle the areas… I am not a computer graphics wiz…and the forum does not let me copy the pics.

In the second picture it almost looks like some of the weakened areas have broken off and been pressed over some areas of the scratches. I would be interested to see if you continued to strop a bit more…whether those bits would just be swept away. In any case those areas are a small fraction of the surface… how important can they be to the overall finish, whether the results of burnishing, flaking, or something else…?? Still real curious about all of this, but not yet a convert…
🙂

Curtis, I will be very interested to see what Clay comes up with if he can look at cross sections of the edge of the edge. As above, I will be extremely surprised if we are moving any metal, let alone enough to change the edge of the edge. But then, I can’t imagine how a knife, or razor, gets apparently sharper when we use strops, if we are truly “rounding” the edge of the edge. If the cross section views are doable, this would be a great thing to look at as well. It would also be interesting to do some of those edge on shots, before and after stropping. Does the edge really get “rounded” making it thicker?? Or maybe are we just convexing a microbevel and actually leaving the edge thinner, but still a V even if only at the true microscopic level.

Phil

[cbwx34]

I noticed in your first pic of the edge at 50 grit that there are some places where the metal looks like it has been burnished in small areas as evidenced by the smoothing of some areas. I am going to see if I can copy the pics and circle the areas… I am not a computer graphics wiz…and the forum does not let me copy the pics.

Here’s the links to the 50g pictures…

http://wickededgeusa.com/media/kunena/attachments/52/50-Grit.jpg

http://wickededgeusa.com/media/kunena/attachments/52/75-CBN-after-50-Grit.jpg

[Phil Pasteur]

One other thought about an experiment. If we want to look at simply burnishing as a property of stropping itself, why not try some Kangaroo or Nanocloth with no abrasive. If we are talking local pressure with the strop, would you not still see it with materials that have minimal (nonocloth supposedly almost none) abrasive properties of there own.

Not sure how to duplicate the stiction… perhaps just the right amount of water or alcohol.

In any case, this might be a sort of “control” scenario. It may help to isolate whether any burnishing that may be happening is due to the strops or the abrasives, or maybe the combination.

Phil

[wickededge]

Hey Phil,

Thank you for all your thoughts. I really appreciate your balanced skepticism and I agree that the idea that leather can burnish the metal defies intuition. Still, I’ve seen some effect that looks like burnishing so often that I haven’t been able to come up with a more competitive theory. At the moment, I’m speculating that the ‘stiction’ is able to apply enough pressure locally that it can move some small amounts of metal around. It is remarkable how much drag I’m able to create with the strops; so much so that they will actually lift up my granite base. I will try some blank strops, that’s definitely on the list though in the past, when using water, I haven’t been able to duplicate the ‘stiction’. I might do better with alcohol, that seems to work very well. I’ve also got some plain paste on order from our supplier so I can experiment with the effect without the abrasives in the equation. Eventually, I’ll get the project with Sandia Labs and their SEM done and we might have a more definitive answer.

-Clay

[Phil Pasteur]

I was thinking that.. at one time, I could do the calcs. Find actual yeild strenght numbers and look at what kind of pressures might be applied through the leather. This would give us a good idea if it is even physically possible to burnish with the entire contact area. Of course the local pressures at the top of the scratch peaks may be impossible to calculate without some serious programing… which is beyond the time I have to actually do. I am at a loss as to how various levels of stiction could be calculated though. Time to go back to the books. I have some vintage 1968 Materials properties texts…:unsure: I was once even pretty good with the Calculus… once.

I also wonder, after reading what you said, if I, with my technique, would ever see the effect. As I mentioned before, I have looked for the amount of compound on the leather with alomost zero moisture content (relative humidity here often in the single digits…but almost always quite under 40% that give me the lowest amount of friction, hence stiction I guess …using very very light strokes… with the calculated intent of simply letting the abrasive do its work. Perhaps this might also be why I can see very little convexing of the shoulders of the edge at 400X as well.

If I was lifting my 16 pound marble base when stropping … I would figure out how to stop it from happening…
🙂

Thanks Curtis for the links… I have a sick server that I am working on tonight…maybe I can get something done on this tomorrow…

Phil

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