To burr or not to burr?

M

MichaelMyers

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Dec 10, 2015
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The common sharpening method of grinding to form a full length burr then repeating with the other side before removing the burr vs grinding until the apex (no light reflecting off the edge) and stop there. I have read from somewhere that creating a burr weakens the edge and result in poor edge retention from fatigue metal and recommends the latter method. How true is this? Edge retention aside, which method produces a sharper edge easily?
 
Raising a burr on one side of a blade is only an indicator, a flag, that is telling the sharpener the edge has reached the point where continuing to remove metal from the present side is fruitless. When the blade is turned over and the same thing is done, the same flag is waving. If the burr is thin enough to be removed easily and the edge is stropped properly the result will be a sound edge without any weaknesses.

The second method only indicates the sharpener has stopped abrading on one side of the blade "before" a burr could be created. The blade is then flipped and the process is repeated. If the edge is then stropped properly, the result will be a sound edge without weaknesses.

To burr or not to burr is just a matter of degree for there is always at least a minute burr produced. If you sharpen under a microscope and can watch the edge being created it might be possible to sharpen an edge without creating a burr.

If both sides of an edge are being abraded at the same time, no burr is created; I can think of no other exception.

Fred
 
MichaelMyers said:
The common sharpening method of grinding to form a full length burr then repeating with the other side before removing the burr vs grinding until the apex (no light reflecting off the edge) and stop there. I have read from somewhere that creating a burr weakens the edge and result in poor edge retention from fatigue metal and recommends the latter method. How true is this? Edge retention aside, which method produces a sharper edge easily?
Click to expand...

An edge which appears to be 'weakened' by forming a burr is simply an edge upon which the refining job (after sharpening) isn't finished yet.

Forming an edge by deliberately avoiding burr formation is a sharpening job that isn't quite finished yet.

It's easy to deal with burrs, so I don't really get why some are afraid to create them to guarantee a fully apexed edge. Burrs are weakened steel; but, if one takes care to properly clean them up, the steel left behind will still be durable and strong. It's easy to prove this, BTW; a cutting test into some wood or heavy cardboard will quickly reveal if the burr (weakened steel) has been adequately removed. If the edge becomes immediately dull after the first cut or two, it's a strong sign a burr was still there, and it folded in the cutting, dulling the edge. On the other hand, if an edge has been properly deburred, it should still easily slice paper or perhaps even shave some hair after a couple or three cuts into wood or cardboard, or more if the steel and heat treat is good and the work done on the edge is first-rate.

I'd bet, 99% of the time, those who attempt to 'just get to' the apex without forming a burr will find their edges are never quite as sharp as they could or should be. It's the source of a lot of posted questions on the forum of 'why isn't my edge getting sharp?' Almost always, it's because they haven't produced and verified the presence of a full-length burr on the edge, and therefore haven't reached a crisp apex yet.

Just make the burr, and then learn and practice how to reduce it and remove it cleanly. I can almost guarantee it'll make a big improvement in your edges. In time, it becomes easier to more quickly notice when the burr is forming, and therefore easier to reduce that smaller burr and refine the edge.

For some cutting uses, an edge which hasn't been burred in sharpening, and therefore hasn't likely been fully apexed, can still work up to the user's needs. A lot of people will go through their entire life using knives that've never been fully apexed when sharpened, and be perfectly happy with that. I used knives that way for most of my life, until I finally figured out my edges could be better.


David
 
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I don't think any human alive could sharpen so precisely that a burr would not form. You would need to be watching the edge with an Electron microscope and controlling the grinding pressure with electronic pressure gauges and CNC mills for accuracy.

Burrs are the result of an abrasive that has passed over the "edge" of a grind plane. All of the debris being pushed in front of the abrasive does not get cut cleanly off of the steel because the steel, though seemingly Hard by our standards, will act more like modeling clay as it's interacting with the abrasive. This Plastic flow of metal results in the burr you find at the edge of two intersecting planes.

So... if you have created a sharp edge then you have at some point created a burr. If not then you have not reached the Apex of two intersecting planes.
 
Lots of thought on this topic.

My opinion it is virtually impossible to properly sharpen an edge without forming at least a tiny burr. If alternating sides every pass you might not even be aware of the burr as it could be mostly ground away with every pass. If running an abrasive across a bevel and grinding to the apex a burr is going to form, or more accurately, the factors working on the steel that lead to burr formation will still be present, even if the burr is not obvious.

I've heard one should avoid working the apex with anything but very fine abrasives, so use the rougher grit to get close to the edge and then finish off on single digit micron abrasives. This leaves the very edge to be worked just as it has been used (in direct contrast to the practice of "destressing" the edge prior to sharpening).

There may be some merit to this fine abrasive edge work strategy, as all grinding does induce subsurface damage to the steel, the larger the abrasive the deeper this damage will go (to some extent). It is unlikely any use aside from the extreme will cause matrix damage in excess of what coarse or medium grit grinding will cause, so leaving it be might very well be the best means of preserving the steels integrity.

Whether it has any measurable effect on edge life is debatable though. The act of smooth 'steeling' an edge certainly is causing the steel matrix to shift through plastic deformation, but the resulting work hardening actually improves edge longevity on lower RC steel. Even on higher RC steel is debatable if there is any negative effect provided the steel does not have large carbides.

Sharpening to a burr is the fastest and only way to guarantee a new edge has been formed. If the burr is properly removed there is no weakness in the edge that will be notable. If there is a lot of force applied to the edge you could end up with a pressure burr where the edge has swayed out of alignment - this could result in edge weakness if it is straightened out and not removed, and could even become a wire edge. Done properly there will be no issues.

For myself I sharpen to a burr and cleanly remove it.
 
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I've done a lot of sharpening by raising a burr on both sides. I've done a very small number of experiments of "no burr" sharpening, ala Cliff Stamp. I was surprisingly successful with no burr sharpening. My test blade was a very easy shape though (wharncliffe).

I think burr sharpening is just fine *if* you know how to remove the burr completely and cleanly. This is what just about every knife manufacturer does at the factory: Sharpen to a burr on a belt sander, then remove the burr with a buffing wheel. Good manufacturers deliver very sharp rather durable blades sharpened with this method.

For the home sharpener, burr sharpening is "a problem" because removing the burr can be tricky without something simple and guaranteed like a powered cotton buffing wheel. Once you learn to properly remove the burr, I think it's less of a problem. Though I must admit that I still occasionally have a problem with the burr on some blades. I'm a slow learner sometimes. :)

Non burr sharpening can be great. But I think it's best on blades that are already in good shape. I think it's much harder on very dull or abused blades. Then there is that final question: When do I stop sharpening? When the reflection disappears, the blade is thin, but is it sharp? I've read estimates that the blade is between 30 and 100 microns thick when the reflection is gone. That's still not "all the way" sharp. The answer I got from Cliff about this was that you learn to judge it based on experience. I suppose you could also do cut tests after every 10, 20, or 30 alternate passes. This is why I like the burr: It's a positive indicator that one side is "done" and doesn't need to be made thinner. <shrug>

I think both methods are valid when done with care and understanding.

Brian.
 
Before the internet, I had never heard of intentionally forming a burr. We had a butcher shop, in our front yard, so we sharpened a LOT. Several professional butchers. All that I ever saw was alternating, edge leading strokes on soft then hard arkies. Got shaving edges or didn't stop. Steels kept the edges in tune until they wouldn't. Then we went back to the fine arkie unless there was a chip.

Now I understand that we probably wasted a lot of time and strokes.
 
Thank you for the comments guys. Great info as always. In my limited testing I seem to get the sharpest edge by grinding to an obvious full length burr then removing it. Which seem to agree with the recommendations by Obsessed and Heavyhanded. I don't have problems with edge retention this way as well. Lately I have been experimenting with no burr ("cliffstamp") method but I can't tell if there's any difference in edge retention yet. Besides its quite hard to tell if I am fully apexed or not without painstaking examination of the edge.
Here's my next question. What's the most effective way to remove the burr leaving behind a clean and crisp edge without stropping? Alternating passes with progressively lighter pressure enough to do the job or high angle passes needed? What about changing the scratch angle?
 
I've tried both and both work. Some steels and knives are infamous for having a particularly tenacious burr. For those steels I avoid forming a burr. These steels are noticeably sharper than when using the but method, though I have much more practice with burr sharpening and can do it faster.
 
MichaelMyers,

There are a few points worth noting here, speaking as someone who is very familiar with both burr based and non burr based (aka three step) sharpening methods:

1) Three step sharpening (Cutting off the previous apex, shaping the edge bevel, setting the apex with a micro-bevel) does not mean not forming any sort of burr at all, but rather not setting out to deliberately form a large, easily noticeable burr along the whole edge. Instead, removing any light reflecting from the apex from a directed light source and the ability to cleanly slice newsprint are used to judge that the edge-bevel has been shaped sufficiently to proceed to the next step. it is entirely possible to unintentionally form a small burr in the process of shaping the edge bevel, and should that occur, it needs to be cut off just as a large burr would need to be.

2) It is important to note that the three step method emphasizes the separation of shaping the edge bevel and the setting of the apex by creating a small micro-bevel at a higher angle than the edge-bevel was shaped at. The higher angle used when creating the micro-bevel removes enough apex height that it not important that the edge was perfectly apexed at the shaping stage.

3) There is no necessity that a burr based method leaves a weaker apex as long as all of the fatigued metal from the burr is cut off cleanly using burr removal techniques (such as alternating elevated passes) prior to setting the apex. Depending on the steel, heat treatment, and size of the burr, it can be surprisingly annoying to remove the burr cleanly. Mind you, some people find this easier than identifying the correct stopping point when shaping an edge-bevel using a three step method. Your mileage may vary.

Personally, I mostly use a three step method because it is faster both in spending less time grinding and in not having to spend time removing a sizeable burr prior to setting the apex with a micro-bevel, but either approach can produce equally effective results in skilled hands.
 
I always burr but that brought up a question I hadn't thought about :

When using the Spyderco Sharpmaker (which I have never used) do you get a burr . I assume not, since you are slicing down edge first. I have watched the video by Sal but it has been long enough I don't recall.

Or are we considering that more of a honing method and so not so much a major sharpening method so it does not apply here. I assume it is enough of a sharpener and not just a hone that it does apply.
 
I don't normally sharpen to where I have a noticeable burr. At least not visible and obvious. But it is almost always there. One way to tell, is to drag it both directions on my nail, or trying to shave both directions. It it jumps a hair one direction, but not the other, there is likely a small burr folded one way.
 
In the past few days I've had a ongoing conversation about this very subject with a friend of mine. He asked about the Cliff Stamp method of creating a bevel and not quite reaching the apex. Then do the micro bevel thing as the final edge. Spread into the conversation was another technique which I refer to as sneaking up on the edge where one carefully reaches the apex and the edge really isn't created until you get to the higher or highest grit. Both can be done with good results and have their merits depending on goals. I've never condoned the micro bevel in general but under certain circumstances it can be very effective. If you have the time sneaking up on the edge has worked quite well for me. Although its rare that I use the technique. As far as burr formation if keeping things to a minimum is the goal both techniques work. The things is the geometry of the item really needs to be close to perfect so you get that perfect edge when you get there. Which is close to impossible without creating a burr of some sort. Not so much with the micro bevel technique as there is room to correct any imperfections during the creation of the final edge. I guess the question is the why of it. For me its a good exercise in sharpening. Just to see how well the technique is working. Easy? No. Less burr formation? Maybe. Worth the effort? Up to you.
 
MichaelMyers said:
Thank you for the comments guys. Great info as always. In my limited testing I seem to get the sharpest edge by grinding to an obvious full length burr then removing it. Which seem to agree with the recommendations by Obsessed and Heavyhanded. I don't have problems with edge retention this way as well. Lately I have been experimenting with no burr ("cliffstamp") method but I can't tell if there's any difference in edge retention yet. Besides its quite hard to tell if I am fully apexed or not without painstaking examination of the edge.
Here's my next question. What's the most effective way to remove the burr leaving behind a clean and crisp edge without stropping? Alternating passes with progressively lighter pressure enough to do the job or high angle passes needed? What about changing the scratch angle?
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The way I remove them:

- Raise and chase with the fewest possible number of flips. The burr attachment point will become progressively weaker the more times it flips, so important to nip it early on.

- Slightly elevate the angle till the burr becomes nearly imperceptible, then remove completely at the original angle.

- If necessary, fold the burr by lightly backdragging across hard plastic or hardwood at 90°, causing the burr to present at a more aggressive angle, and remove as above.

- Strop on plain paper wrapped around a hard surface as a final or semi-final step. This will shine up any residual burrs and can even remove smaller ones.

- A quick and dirty method is to drag the edge through some plastic or hardwood every alternating pass as you get to the final strokes. It works, but sometimes can make parallel scratches that make burr detection harder, not easier. Quick and dirty and not completely effective, but I have gotten very good results with it.

In my experience, changing scratch pattern angles does not improve burr removal as it doesn't do anything for presenting the burr at a better angle to the abrasive, but it will reduce scratch depth allowing a slightly more refined cutting action from a given stone. Is also possible for the resulting scratch pattern confusion to hide residual burrs.

Alternating passes can work, but one also needs to makes sure the contact is equal on both sides of the bevel. It only takes a few passes with poor contact on the opposite side to undo a bunch or work. I prefer to alternate sides every few seconds of initial grinding till I'm just starting to make a burr, then work one side till its 100%, flip, eliminate.

If I have to chase it side to side a few flips is OK, as long as it is becoming notably smaller every flip. If I have to chase too many times I'll cut it off and start over, but that does not happen often.

I do 80-90% of my sharpening by feel. Feel the edge contact on the stone, feel for the burr as it forms, feel it disappear. Generally I only look at the stone enough to see that I'm working the entire surface or working my waterstones evenly. Often the final visual inspection turns up nothing or only what I expected to see based on what I could already feel, maybe I missed a warp or didn't completely flip the burr on the second side etc.

My gold standard (tho I seldom do this anymore) is to very very lightly backdrag the edge on the plastic or hardwood at 90° and look to see if anything has turned up. If nothing turns up, the edge is certifiable burr free. Paper stropping works very well and seldom passes an edge that won't pass the drag test anyway.

Another thought, in many cases the presence of a small incomplete burr will not even be noticeable to most people when cutting or in terms of longevity. While I always intend to eliminate the burr completely and am pretty good at doing so, I have gone 180° on this topic since I started taking my sharpening more seriously. It is better to leave some sporadic micro burring than to eliminate it 100% if doing so means overworking the edge or making the terminal angle overly broad - the former leaves the edge in better cutting shape than the latter. Keeping in mind I'm talking about burrs that cannot be readily detected by touch or naked eye.

Lastly, different abrasive surfaces will make different burring levels. Most waterstones, SiC stones, and wet/dry create less burring than hard fixed abrasives. Having a preference for one type of abrasive surface over another will lead to preferences in finishing technique, and these techniques are not going to work equally well across the board.


From the manual:
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Wowbagger said:
I always burr but that brought up a question I hadn't thought about :

When using the Spyderco Sharpmaker (which I have never used) do you get a burr . I assume not, since you are slicing down edge first. I have watched the video by Sal but it has been long enough I don't recall.

Or are we considering that more of a honing method and so not so much a major sharpening method so it does not apply here. I assume it is enough of a sharpener and not just a hone that it does apply.
Click to expand...

Used with a very light touch, the Sharpmaker's rods will behave like any other sharpening media, in the sense that it's capable of burring an edge, but no more or less than any other tool. It's up to the user's touch, in that sense.

On the other hand, if used with even a slightly too-heavy touch, I've found the ceramics like the Spyderco rods can produce absolutely huge burrs. They don't handle heavy grinding well, in that regard. I think a lot of that has to do with how fast ceramics can load up with swarf (very fast under heavy pressure). Once that happens, the abrasive can no longer function well, i.e., cut the steel cleanly, and the abrasive then does essentially nothing but create burrs and/or stop cutting altogether; the pressure used will quickly fold or bend the fine edge away from the hone (effectively becomes a burr or wire edge), instead of cleanly cutting or stripping the weak metal from the edge.

The pics below are of a Victorinox paring knife's edge with a lengthy and partly dislocated wire edge (burr), after I'd done some fairly heavy scrubbing on a Spyderco medium bench stone. By naked eye, it first looked like a fine fiber stuck on the edge from a microfiber towel I used to wipe down the blade (I had assumed a fiber hung up on a small burr); but looking under magnification revealed quite the surprise. :eek:
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David
 
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Wowbagger said:
When using the Spyderco Sharpmaker (which I have never used) do you get a burr . I assume not, since you are slicing down edge first.
Click to expand...

I go to a burr on both sides about 95% of the time I use the sharpmaker. Like using any other sharpener, the burr if the affirmative indicator that you've finished grinding one side.

I did this just 2 days ago on my main Gyoto that I use in the kitchen. The resulting edge (from medium rods only) was very satisfying and REALLY bit into the chicken I was butterflying right afterwards.

Brian.
 
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