To bur or not to bur that is the question

It is unfortunate that cliff (the guy in the video) is now banned from BF. (I was absent from the forum for a long time, didn't know why and how) He has tremendous knowledge, albeit a lot of time it's hard to understand ;)

To say Sal acknowledges his input is not a small thing. Am saying this not to belittle the experts here, from whom I have learnt a lot, but a subject as complex as steel meeting abrasives, different angle (point of view) always bring new understanding, at least to me IMHO.
 
knifenut1013 said:
Burrs don't fold or switch sides it gets re-created by new material removal and change of direction.
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Respectfully disagree with this, tho on some very hard steels it might be the case. How else wire edges (unless I'm misunderstanding something here)?The burr formed by grinding can absolutely be flipped from side to side - this can even be done with non abrasive materials as when backdragging the burr edge at a steep angle along some hardwood or similar. Its not even possible to know exactly what the connection point between burr and apex looks like much of the time, you'd have to slice the blade crosswise somehow to get a true look at it.
I also suspect the apex can sometimes be folded into something of a very shallow 'S' depending upon pressure, type of steel, and inclusive angle, making it even more interesting to tell where the burr stops and the apex begins.

This as a very complex discussion on some levels...
 
I'm guessing now, but I suspect that a burr can be either or both folded to the other side or ground off entirely by the stone and recreated on the other side.

The point of steeling an edge is to realign the edge where it has become very slightly folded to one side. A burr can act like that under very light, non-abrasive pressure. But in the normal course of sharpening -- especially with coarse stones -- it is ground off and replaced on the other side with new metal. When you have reduced the burr through lighter strokes and finer stones, I suspect there is some folding going on, too.

Me2 raised an interesting question about whether the burr is ever completely gone. I don't know. I do know that a lot of people think they have a hair-shaving edge when it's really just a wire edge that will fall off under harder use and leave a much duller edge.

The other interesting question was about work hardening. Again, I don't know, but I'd think that fatigue would be a bigger problem. The fact that we steel knives in critical occupations, such as cooking, is pretty good evidence that the steel at the apex of the edge is getting moved around. That repeated bending would fatigue the steel, so when we do a major resharpening, as opposed to steeling or stropping, we'd want to remove that old metal, which means we'll get a good burr.
 
HeavyHanded said:
Respectfully disagree with this, tho on some very hard steels it might be the case. How else wire edges (unless I'm misunderstanding something here)?The burr formed by grinding can absolutely be flipped from side to side - this can even be done with non abrasive materials as when backdragging the burr edge at a steep angle along some hardwood or similar. Its not even possible to know exactly what the connection point between burr and apex looks like much of the time, you'd have to slice the blade crosswise somehow to get a true look at it.
I also suspect the apex can sometimes be folded into something of a very shallow 'S' depending upon pressure, type of steel, and inclusive angle, making it even more interesting to tell where the burr stops and the apex begins.

This as a very complex discussion on some levels...
Click to expand...

I'm also certain a burr can be folded, with a minimum of abrasion. On stubbornly ductile steels (420HC, VG-10, ATS-34), I've used a small black hard Arkansas pocket stone to 'flip' burrs from one side to another, often within a pass or two. The abrasion from that particular stone is minimal on these steels, and the burrs/wires can be flipped with some pressure applied, as I 'slide' the stone along the length of the edge. This is actually a convenient way to verify the presence of a burr/wire on an edge, when I can see it move from one side to the other. I use that Arkansas, at times, because it's a little easier to lean into it a bit while polishing a bevel (often with some oil on the stone), without over-grinding the edge itself. I've also used a Spyderco ceramic DoubleStuff hone that I lapped to UF or finer (it's almost glassy), for the same purpose and with similar behavior.


David
 
I saw that video too. I think it's misleading. Forming a burr is not a bad thing as he claims. Effort should be made not to form a huge burr. And that's what he does when he almost achieves a burr at a low angle and then jumps up to a higher angle to form a microbevel with very light pressure. Is there no burr formed at that higher angle with light pressure? There is a burr, IMO. It's just a very small one and probably not an issue.
This person also claims that stropping is just a bad thing, period. He's very dogmatic and while he's knowlegable I find his arrogance to be a little much.
There are many different ways to sharpen.
 
Basically, you get burrs from dragging the edge (spine-leading). Burrs are a good indicator for knowing when you've reached the apex for the side you're working on, but not necessary at all for a seasoned sharpener. I'm not an official expert at sharpening -- although I do seem to know more than most professional sharpeners in my area. I almost never work up a burr (feels like a waste of metal!), yet my edges are scary sharp and stay sharp too. Honestly, the only time I ever see a burr is when I grind a blade on a machine. The characteristics of the burr will also depend on the steel. Hard steels don't leave as much of a burr as the really soft ones.
 
A burr can be bent by non abrasive contact but that's not what I meant. What happens when you grind on a stone and remove metal? Your removing "layers" of metal removing burrs and making new ones at the same time. For a burr to be bent on a stone no metal could be removed, but that's not the case.

I'm sure there is some level of deformation going on but with abrasive sharpening you are in a constant process of removing metal.
 
knifenut1013 said:
A burr can be bent by non abrasive contact but that's not what I meant. What happens when you grind on a stone and remove metal? Your removing "layers" of metal removing burrs and making new ones at the same time. For a burr to be bent on a stone no metal could be removed, but that's not the case.

I'm sure there is some level of deformation going on but with abrasive sharpening you are in a constant process of removing metal.
Click to expand...

Not necessarily, a burr formed by a edge-trailing stroke on a very fine apex could bend if the edge angle is raised too much, too much pressure is used, etc. It's still removing metal but it bends the edge one way or the other
 
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