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

PhilipPasteur wrote:


Here's the links to the 50g pictures...

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

wickededgeusa.com/media/kunena/attachmen...BN-after-50-Grit.jpg

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

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.

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... 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

So after my head was done pounding reading this, following all the associated links, and marveling at the pretty pictures...one thing stands out.

Clay, how much pressure are you using when stropping? I *have* to assume you use equal pressure thru the process, but how much? I saw mention of lifting the base edge when stropping, which implies lots of pressure....

I guess I was trying to hint at the same question. Considering the repeated advice given all over this forum to use very light strokes when stropping...indeed with all of the stones, I wonder how many are lifting their bases when stropping... and if not, if anyone would be seeing similar results to what Clay has seen... whether these results are the result of true burnishing or not..
??

Phil

PhilipPasteur wrote:


Just a brief quote from Clay:

wickededge wrote:


I don't know whether you've read the posts on my blog regarding stropping, but in some experiments I did over 500 stropping movements per side. That is a lot , and in order to see effect more quickly I used quite a bit of pressure.

My pictures are not nearly as good as Clay's, but my conclusion was definitely that burnishing occurs, and that the WE pastes excel at doing this. That's why I started this threat . You can read all of my posts on stropping here .

That is not to say that the common knowledge that you have to strop lightly is a myth. I don't know exactly where the idea of stropping originated, but it has been widely used in the straight razor world for over a 100 years. If you use too much pressure on a straight razor, with an edge that usually has an acute angle and is very thin, you simply destroy the edge. Also, if you strop just to remove a burr (which is not necessary when you're using a WEPS), you don't need much pressure. And if you're stropping free-hand, a mistake is made easily if you use pressure, so you'd better be safe than sorry.

Even with a WEPS, if you use a lot of pressure with a leather strop and don't adjust the angle, you will round the edge. So setting back the angle (with leather I do 1 or 2 degrees) is necessary if you use a little force.

In my normal sharpening, I don't use much pressure when stropping. When I'm going for serious polish though, I use pressure at a lower angle at first and then lighten up as I get ready to finish.

The thing about lifting the base - I'm not necessarily trying to lift the base, but once my strops are well seasoned, they have enough grip that I have to try not to lift the base and have to lessen the pressure.

[quote="mark76" post=6622]
wickededge wrote:


I would never have intrepreted "Firm" to mean so much pressure that he was lifting the base on each stroke.

mark76 wrote:


I did and I commented on them previously.

mark76 wrote:


I think that sometimes we can start out doing an experiment with a preconception. The results will always tend to confirm that idea if we are not very careful. It is easy to just intrpret the results in a manner that confirms the theories we have going in.

I don't think you can see evidence of the kind of burnishing that Clay is talking about with 400X. This is why he wants to get time on an SEM to verify his theory.

mark76 wrote:


I will look for the thread. I distintly remember Clay suggesting that just a few light strokes with leather would make a significant improvement at the edge. I think this may have been mentioned a few times actually. The suggestion was clearly that we did not need to do 500 strokes while lifting the base to get an improvement.

The point was not whether stropping with a light touch is a good idea, which I think in general that it is. The point was, if the majority of people do it this way, with any practical number of strokes, they would likely not see the effects that we are discussing.

Phil