To Burr, or Not to Burr....That is the Question

AFAustin

AFAustin

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Jun 8, 2004
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Well, my question at least. Here's what I mean....

Standard sharpening technique is to get a burr along the entire edge with the first stone, or belt, or sandpaper, before moving to the next somewhat finer stone, belt, or paper. Is this always necessary?

I confess that I'm not the best at detecting a burr in the first place. But I can tell pretty closely when I've apexed the edge, mainly by constantly testing by cutting paper (copy and phone book) as I'm sharpening.

When initially setting an edge, I typically try to get pretty close to the apex with the first medium (typically a 65 micron belt on my Work Sharp KO), but I don't insist on a complete apex. My thinking is that if I am fanatical about that, I may keep on and keep on and in the process remove too much metal (this is the first and coarsest belt, after all). So instead, I stop on "close" with the first belt, and then go to my second, slightly finer belt. I may achieve my apex with it, or I might even settle for getting a little closer and then move on to #3. I'll get my apex on this one, and then I'll progress through the remaining belts to refine and polish the edge. (To set an initial edge, I'll usually do a 6 or 7 belt progression.)

So, am I wrong to "sneak up" on the apex and try to keep a bit more metal on my blade? Is there an inherent advantage to always getting a complete burr/full apex on the very first (and coarsest) stone/belt/paper?

Thanks for any wisdom.

Andrew
 
Sneak-up is fine as long as the apex is free of undulation (dip/dent/chip). In event of undulation apex, flatten the apex first before proceed with sharpening.

Depend on knife condition and blade attributes, I always raise burr between abrasive size 100um (120grit) and 15um (1K). at 15um raise burr around 2-8um in size, which smallest I can realistically feel with my fingers. Note that - total burr size/length is usually always longer than blade width loss. e.g total 1mm burr is at most translate to 1mm blade width loss, for most blade below 61rc blade width loss will be less than 0.5mm (just a quick guess, but not that hard to prove anyway). Pick smallest abrasive appropriate for the initial grind is a best way to save metal. Sneak-up could sometime lead to regress to lower grit, ah heck - why not burr right the first time :)
 
Different steels will be more or less likely to form burrs easily, so I've sometimes stopped short of deliberately looking for them. However, with some that I assumed at some point wouldn't form much of a burr, I sometimes discovered later that a different sharpening method or abrasive would force them more easily, and sometimes show me a little more about how fine the edge on the steel could get. In other words, I figured out I was sometimes short-changing myself out of some sharpness by not progressing all the way to an obvious, verifiable burr. This is why I'd much rather take it all the way to the burr, to be absolutely & positively sure the edge is as fine as it can be. I don't worry about the extra little bit of steel that might be sacrificed in chasing the burr, so long as I know I can get it there.

Some combinations of steel vs. abrasive type can make it tricky, in seeing the burr when it forms. I've noticed this at times, in sharpening 'softer-than-usual' 1095 with a diamond hone. Took me a while to figure it out, but the diamond was working so aggressively on the steel that the burr could literally form and be immediately scrubbed off in a single pass. I really had to slow down, lighten pressure and inspect the edge after each stroke, to catch the burr as it formed. Otherwise, I would've just continued to scrub off a whole lot more steel than was necessary.

(BTW, I can see the value in 'sneaking up' on the apex with the coarsest abrasive, then forming a verifiable burr with the next or subsequent finer grits. I've often done this with diamond hones, as I found it much easier to form an obvious burr with a 'Fine' diamond, after roughing out a passable new bevel with the 'Coarse'. Important point being, I'm still looking to form the burr, just to make sure the edge is fully apexed.)


David
 
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Recently there was a thread on the CKTG forums about "destressing the edge" before sharpening, by cutting lightly into a stone to remove metal from the apex. The guy that coined that term is really controversial and it generated a bit of non-productive discussion. Once that died off, I learned something. He advocates doing this edge removal technique and then sharpening and looking at the reflection from the apex of the edge, while looking straight down at it. After cutting into the stone, you will see a full length reflection and it's rather obvious.

As you sharpen, the reflection will get smaller and smaller until you can't see it with the naked eye. At this point, he says the edge is 20 um wide or smaller. Now here's where the burr comes into play. He says you then should do finishing strokes, back and forth, going lighter just as you would at the end of any sharpening session and *never* form a burr at all. You will probably form a small one at some point and perhaps scrub it right off, as that's the nature of sharpening. But (according to his method), you shouldn't be trying for a burr at all.

As an experiment I did this with my Spyderco Yojimbo 2. Admittedly, this blade is very easy to sharpen because of the wharncliffe shape. Even after just the coarse stone, this blade was quite sharp and cut phonebook paper cleanly. After the fine stone it cross cut phonebook paper and popped hair off of my leg. This method works for sure. For me, the unknown is when to stop, since there's no affirmative indication as a burr gives me. Shame on me; I should have done more experiments with more blade shapes, but I have yet to do any other blades this way, so I'm not sure how well it works overall. It certainly works for the man who advocates this technique, as evidenced by his videos.

I think "non-burr sharpening" definitely has merit.

Brian.
 
If your taking the time to progress thru 6 or 7 grits a sneak attack could work. However, I use stones and only take the time to do 2 grits as I'm not OCD. So, I look to feel a burr on the first stone. Before moving to the finer grit. You might can save some steel by not arriving at a burr on the coarse grit but you then negate this by eating on the steel for 6 more grits. DM
 
Gentlemen, thanks for your comments.

I should add that there's actually another reason why I often "stop short" on the first grit besides the desire to save metal. With that first coarse grit I am also forming and shaping my initial bevel, and when I get a nice shape and symmetry on it, I am inclined to stop even if I haven't fully apexed the edge (as long as I'm close). I have found that if I keep going past that point, I might get a full apex but at the expense of my "pretty" bevel (yes, I confess I like pretty :o).

Andrew
 
I agree with keeping the burr as small as possible, but I do not believe its possible to have 'no burr sharpening', at least not without spending a great deal of time finessing the last little bit. I also do not believe there will be any real difference in steel loss, but will be some uncertainty as to how complete the job has been. All grinding produces a burr, no abrasive is 100% efficient. The difference between no burr at a given point and a very small one could be as narrow as a couple of light passes beyond what is needed to apex. IMHO it is a lot faster and easier to raise an even burr and use my finesse effort to remove it cleanly - is a known quantity at that point. Approaching the apex at various points along the edge, all is an estimate. I cannot imagine working a machete, hatchet or larger kitchen knife in this manner and am unwilling to use multiple strategies for different tools based only on size or shape.

Hey, As long as it works, use it. In theory there's no reason why it shouldn't give good end results.
 
I raise a burr with the coarse stones, i.e. 1,000 and below. I try to not raise a burr at 2K and above. I use a magnifing glass to insure that it's apexed.
 
N(not burr) method will merge into B(urr) method if/when burr taken place in N at a finer grit in the progression. I prefer method B because it is more deterministic. Below are reasons why I prefer B.

In N - beside possibility of minor metal saving, here are possible downsides:

a) prematurely progress to finer grit

b) uneven apex width due to skills (sharpening movement & blade flex) - lead to (a)

c) false visual when burr/wire cover up the apex (e.g. per CliffStamp 20um flat top apex approach - thus two 90* edge top, burr/swarf will flow over the 90* edge top)

d) at higher/fine grit, choice of abrasive will depend on type/ht of steels. Would be bad to burnish bevel metal to form a false/weak apex, right ;)

my deficit 2cents
 
If you don't bur a dull knife, you will not be sharpening the knife.
 
I go for a burr when sharpening but majority of the time when I polish I don't go for burr.
 
There is no need to raise a burr, though it does let you know you have overshot the apex all along the edge. I sharpened without raising a burr for many years and could get face shaving edges that way. Then switched to burr based sharpening and could get the same results. Some small burr is probably unavoidable once the apex is reached, but forming one that is detectable with your fingers or unaided eye isn't necessary.

Avoiding a burr also makes sharpening those stubborn steels easier. Some steels (I'm looking at you 420J2) will hold onto a burr like grim death and it takes a lot of knowledge to get rid of it. In these cases, it's best to avoid them altogether.
 
me2 said:
There is no need to raise a burr, though it does let you know you have overshot the apex all along the edge. I sharpened without raising a burr for many years and could get face shaving edges that way. Then switched to burr based sharpening and could get the same results. Some small burr is probably unavoidable once the apex is reached, but forming one that is detectable with your fingers or unaided eye isn't necessary.

Avoiding a burr also makes sharpening those stubborn steels easier. Some steels (I'm looking at you 420J2) will hold onto a burr like grim death and it takes a lot of knowledge to get rid of it. In these cases, it's best to avoid them altogether.
Click to expand...

:thumbup:
I learned this lesson with softer 420HC (Case) and VG-10 (Spyderco) as well. I go to great lengths to minimize the burrs that do form on those, for the same reasons. :)


David
 
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