To bur or not to bur that is the question

R

Robert Ptacel

Joined
Feb 1, 2007
Messages
314
I've always ground a bur on both sides of the blade while reprofiling an edge to ensure I reached the apex.I was watching a guy on Youtube that said doing so only introduces more fatigued steel into the equation.He only ground to the point when he neared the apex then went to his final edging and his edges turned out remarkably sharp.Obviously this takes experience on his part but I was intrigued.What say you?
 
Intentionally forming a burr is not necessary. I sharpened for years without doing so. I would cut off the old edge on a fine ceramic rod, then sharpen until I couldn't see the shiny flat spot any more. Then I'd go to the next finer stone, then finish off on the ceramic rod. I didnt cut into the edge to remove weakened metal, but to have the whole edge start from the same point of dullness and not have one section sharp before the others.

Forming some degree of burr is probably almost unavoidable. One pass beyond apexing will produce a burr. When sharpening really problem steels, I'll sometimes stop short of forming a burr or form one and cut it off at 90 degrees to the stone, then start alternating passes to sneak up on the edge without forming one. This is for knives that hold on to a floppy burr for dear life. No cutlery grade steel has to behave this way, but many cheaper knives do for various reasons.
 
When you grind steel you form burrs, the size of the burr will depend on the amount of pressure used and the grit size of the abrasive. It's not something you can avoid.
 
knifenut1013 said:
When you grind steel you form burrs, the size of the burr will depend on the amount of pressure used and the grit size of the abrasive. It's not something you can avoid.
Click to expand...

Jason has it. You can, if you are careful and very, very observant, sneak up on an apex to ensure that the burr is very, very small, but you can't avoid it and still get a sharp knife.

I doubt that burr formation fatigues the final edge. The burr and surface metal on the edge get ground away as you lighten strokes and move to finer stones.

I think the bigger danger in trying to avoid a burr is in leaving the edge or sections of the edge dull.
 
I always work to a bur. That is how I know that I am done with that side.

Granted on some stainless steels, provided that they have been profiled properly, I just hit both sides equally until it will shave. Stainless is such a hassle sometimes
 
me2 said:
So every edge has a burr on it?
Click to expand...

Interesting question.

I sharpened my Rukus (S30V) last night. It was dull and dirty from heavy use. The blade was most dull in the center, where most of the cutting had taken place. So I raised a burr, as usual, the entire length of the blade. The burr came up quickly at the near and far ends of the blade, but took longer to raise in the dull center. I slightly over-sharpened the ends of the blade so that the line of the edge was not changed.

On course diamonds (100 grit) the burr was fairly big. But as I reduced stone pressure and moved to finer stones, the burr became progressively smaller. By the time I stropped, I could no longer find a burr with my fingers or loupe. But I suppose there was still a very tiny burr there, but too small to make much difference in edge performance.

But the big factor is that the burr forms when a stone passes the apex. And you can't truly sharpen an edge unless you bring the stone to the apex.
 
me2 said:
So every edge has a burr on it?
Click to expand...

Depends on how good the sharpener is ;)

It's not that every edge has a burr but all abrasive grinding caused deformation, burrs, and debris.
 
What are some tests to ensure you do not have a burr? If I can whittle hair in both directions, and cleanly push cut ( true push cut ) phonebook paper in both directions I am happy.
 
Robert Ptacel said:
.He only ground to the point when he neared the apex then went to his final edging and his edges turned out remarkably sharp.Obviously this takes experience on his part but I was intrigued.What say you?
Click to expand...
i'm a bit like this. for one thing, some steels don't burr up (like zdp 189.) i view the edge using a lens with the point towards me, allowing me to see from a shallow angle how the new profile is shaping. the original polished bevel can easily be seen and i stop just before the original bevel right on the edge completely disappears.
 
[video=youtube;OPGGo3W15HQ]http://www.youtube.com/watch?v=OPGGo3W15HQ[/video]

This might be the guy the OP is talking about. At about 2:20, he talks about how burrs are bad.
 
Edge-leading at 2:05 which essentially he created a micro-bevel + minimize-burr and deburr at the same time. For the edge to be sharp, the edge gotta be apexed at this time because he lowered the angle in sub-sequent strokes, which soften the micro-bevel shoulder. I feel this is a slight of hands which can be confusing for viewers/learners. At 2:05 that angle must be at least 30* per side (unless my eyes need a new pair of glasses). Rephrase other posters statements - it is not possible to achieve 100% clean apex without create some sort of burr. Otherwise you would end up with 1 tiny edge area of perfect apexed and the rest of the edge is not there yet.
 
bluntcut said:
Edge-leading at 2:05 which essentially he created a micro-bevel + minimize-burr and deburr at the same time. For the edge to be sharp, the edge gotta be apexed at this time because he lowered the angle in sub-sequent strokes, which soften the micro-bevel shoulder. I feel this is a slight of hands which can be confusing for viewers/learners. At 2:05 that angle must be at least 30* per side (unless my eyes need a new pair of glasses). Rephrase other posters statements - it is not possible to achieve 100% clean apex without create some sort of burr. Otherwise you would end up with 1 tiny edge area of perfect apexed and the rest of the edge is not there yet.
Click to expand...

Yes, this is the very video I was referring to.
 
I just don't agree with this assessment of burrs and what they actually are. They sometimes create a "fatigued edge" more commonly referred to as a wire edge, but I don't agree that it happens whenever a burr is formed and they're usually removed with the continued honing process. The real problem is when instead of "wearing" the wire away, people simply stand it out straight on the edge, and the knife will dull on the first cut into something.

The only other thing I think he could be talking about is more like the edge actually bending to one side, but that isn't really because of a person forming a burr, but because of a person using too much pressure while doing so.
 
I've been wondering if the act of folding a burr doesn't create a 'work-hardening' effect localized at the very apex - maybe a bit of folding is good, too much is bad. I have no idea how to control for this or test for it. Edge testing tends to be very subjective and methods of prep are difficult to get exactly correct. Some forms of grinding and some abrasives will create larger burrs or have a tougher time removing them - much depends on the steel.
 
Burrs don't fold or switch sides it gets re-created by new material removal and change of direction.
 
You must log in or register to reply here.
Back
Top