A mutant burr

[grepper]

I was down to only one sacrificial knife for testing and experimenting, so I went to the local Salvation Army store to see if they had anything interesting.  Occasionally I get lucky and find something nice, but this time not so much.   90% of the knives were worn out serrated pieces of that shiny stainless spring steel crap, whatever that stuff is.  I did find one 7” Santoku for $1.99 and a little 3.5” paring for $0.99.  The steel seemed to be the next step up from the shiny spring steel stuff, but nothing special at all.
 
I decided to sharpen them both with a new, unused 120 grit Cubitron II belt because I wanted to break in the belt.  When those belts are new they are extremely sharp and aggressive, but calm down to just right after break in.
 
The cheapo little paring knife couldn’t take such a coarse abrasive and the edge just crumbled away in chunks rather then getting sharp.  I didn’t really care, so I bailed and moved to the Santoku which was far more interesting. 
 
The Santoku had no problem with the coarse abrasive and formed a large, heavy duty burr.  I started deburring with light pressure, 45° angle strokes on the rough side of a leather belt.  It was easy to see the burr bending back and forth.  I did that for awhile.  Then a while longer.  The some more.  The burr just kept bending and bending and bending…
 
So then I started applying more pressure and counted 26 strokes on each side, plus some occasional strokes at almost 90° to the belt.  After that the burr seemed mostly gone, but under a good light I could still see a hint of burr.  I took 3 sharpness readings: 150, 155, 165.  So I deburred more.  A lot more.  Maybe another 20 on each side.  That kind of thing.  Then I took readings again: 140, 145, 150. 
 
Every so often I run across a blade like that.  Whatever that no-name steel is, it creates an extremely malleable burr that is highly resistant to deburing.  Far, far more difficult and time consuming than most knives.  Almost like the burr was made of gold.  The stuff just bends and bends and bends and bends and…  It’s almost flabbergasting.  How can such a thin little piece of steel be so resilient?   Had I not seen it before, I might have even been gobsmacked.
 
I guess it just goes to show that no two burrs are created equal.  It also shows the importance of carefully checking that the entire burr is removed as the effort required for complete burr removal is potentially highly variable from blade to blade.

[SteveG]

Is it possible that in the process of removing the existing burr, you're also drawing new metal out past the apex and creating a new burr? (I ask because I've done that, though it took me a while to realize it - and I still don't know how to tell when it's actually happening.) I don't know if it's theoretically sound or not, but I can visualize it where stropping might actually build up the metal where the burr is attached, creating an extremely frustrating sharpening session.

[grepper]

That is an interesting idea Mr. Steve, and our esteemed fellow forum member Mr. Jan spoke to the effects of burnishing in some post or another when the subject arose before. 
 
I guess microscopically I wouldn’t be surprised if something like that might be happening to some degree.  That said, I am doubtful that the contact stress generated with the leather belt is sufficient enough to exceed the yield strength of the steel surface to such a degree as to significantly add material to the burr.
 
Due to my appreciation of a toothy edge, the deburring I do with a leather belt is with extremely light pressure so as to minimize degradation and smoothing of same.   Friction generated between the belt and the blade is never enough to generate any noticeable warming of the blade whatsoever. 
 
The burr on the blade was big enough to easily be seen with the unaided eye.  It was a big, gnarly burr.  What I found truly amazing was that I was able to bend that thin little piece of steel back and forth at a 45° angle something like 25 to 30 times before it started to fracture off.  That is some malleable stuff!  I eventually got it done, but it took significantly longer than usual.  It would be interesting to know what kind of steel it is and its hardness.

[SteveG]

I'm curious, do you use any abrasive on the leather belt? I'm sure you have a lot more experience sharpening than I do, so I feel a bit awkward giving my input, but even with light pressure I would think that an unloaded strop might cause a lot of plastic deformation right at the apex (i.e., the base of the burr). If your BESS reading is around 150, that should translate to an apex dimension of about 1.5 microns, if I understood the docs correctly. On a belt running at any speed, I would think that many, many millions of microns of leather would travel across the edge, and some metal would move with that. But I have zero experience belt sharpening or stropping, so don't know what to expect. (I strop on an 8-inch piece of mounted leather, and usually only take a few strokes with light pressure - works fine for chisels and plane-blades, but seems to make my knives worse, so I'm obviously missing something important.)

If you're using a loaded belt, then I would expect the burr to be abraded away. Whether it can be abraded away faster than a new burr could be created I have no clue, but I imagine the new burr wouldn't be visible without magnification.

I've had times when feeling for a burr that it comes off in my fingers (hard, non-stainless steel). Wonder if you would have been able to just pull it off.

Maybe soft stainless steel is just that way by nature.

[Jan]

Mike claims that the apex width of a standard DE razor blade is 0.1 micron.

When the width of 0.1 micron corresponds to 50 gf on the BESS scale, than 150 gf should correspond to a width of 0.3 microns. This linear relationship should be valid up to 300 gf BESS readings.

Jan

   

[SteveG]

Thanks for that clarification Jan, I had misread/misremembered that, appreciate the redirect.

Steve

[EOU]

Thank you for for the question Steve and thank you for helping with the answer Jan. This is a topic that seems to be somewhat like the size of our national debt, an almost incomprehensible figure. The important thing to grasp here is that a fraction of a micron is a miniscule amount of metal and 20 trillion is a lot of money.