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To burr or not to burr?
- Thread starter MichaelMyers
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Thanks. The wire edge was enough of an eye-opener to me, that I felt it deserved a pic or two. In one look, it illustrates what a burr or wire edge looks like, how it can eventually break away from the edge AND how tenaciously some burrs can hang on, and how relatively clean and sharp the remaining edge can be, after the burr breaks away.
After the bigger portion of the burr came off, the edge was pretty sharp, but still warranted some stropping to clean the remnants up. I tested the sharpness by slicing phonebook pages, on which some small remaining bits of the burr were snagging a little bit. I was 'experimenting' with a couple things at once; the Spyderco medium stone was part of that, because it was previously little-used and I wanted to get reacquainted with it, even trying the stone with some mineral oil. The other part was an improvised green compound-on-cork strop I was trying out. In the 2nd pic of the closer view, some of the green-tinted cork bits can be seen clinging to the blade, after I'd given it a couple swipes on the strop. My Victorinox paring knife has frequently been the 'crash test dummy' for such experiments, because it nicely rewards the things that work with a screaming-sharp edge, but won't respond to sub-par ideas of mine. Sort of 'inconclusive' results with the cork strop this time around; most of that wire edge I subsequently stripped off by draw-cutting into some wood, and then did the finishing touches on my good ol' reliable leather belt with some green compound.
David
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HeavyHanded,
Personally, I've gotten the best and most consistent burr removal results by using 1-2 light alternating passes per side at double the angle the edge bevel was being shaped at, followed by ~3-5 very light alternating passes per side at the original angle the edge bevel was being shaped at.
MichaelMyers,
Incidentally, I will also note that burr minimization in the edge bevel shaping stage is also aided by using highly friable sharpening stones (i.e. the muddiest waterstones you can get) as the slurry released by the stone works automatically to minimize burr formation as it impacts the apex on edge-leading strokes. The slight rounding of the apex produced by that slurry is not a problem in a three step method as the apex is set afterwards anyway (ideally with a non-friable abrasive that will not produce any rounding with edge leading strokes).
Personally, I've gotten the best and most consistent burr removal results by using 1-2 light alternating passes per side at double the angle the edge bevel was being shaped at, followed by ~3-5 very light alternating passes per side at the original angle the edge bevel was being shaped at.
MichaelMyers,
Incidentally, I will also note that burr minimization in the edge bevel shaping stage is also aided by using highly friable sharpening stones (i.e. the muddiest waterstones you can get) as the slurry released by the stone works automatically to minimize burr formation as it impacts the apex on edge-leading strokes. The slight rounding of the apex produced by that slurry is not a problem in a three step method as the apex is set afterwards anyway (ideally with a non-friable abrasive that will not produce any rounding with edge leading strokes).
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Is there evidence of this? I find burrs on knives sharpened on stones with slurry... I'm not sure how effective loose grit would be at preventing a burr from forming. My understanding is slurry is typically created simply to help the stone cut better, and/or for a better polishing effect in some cases.
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Anecdotally,
the lose grit acts like a lapping mechanism. In effect it reduces burr formation (all else being equal) but also limits how fine the edge might get - with a leading pass anyway.
Part of burr formation is related to how firmly fixed the abrasive is. The more rigidly fixed it is, the more likely it is to hook into the steel and draw it out a bit or deform it out of position depending if trailing or leading. Abrasives with some mobility will shift if they embed too deeply or impact too directly into the steel, limiting the size and frequency of the burr formation.
Stones with very weak binders might not barely even form a burr, but that type of stone wouldn't be used for hand sharpening.
It is my understanding that with the buckyball shape of garnets, a Coticule will cut more rapidly/deeply with a slurry. In practice I find some stones cut faster with a slurry and some cut more slowly, haven't noticed a consistent effect.
This is also a good strategy IMHO for finishing off with a smooth steel or smooth glass. Bigger margin of error than if finished to a fine edge, and allows for more touchups before the edge becomes drawn out.
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Guess I'm not seeing how the loose grit can 'lap' the top of the blade where the burr is forming. I can (in theory) see it affecting the very edge, where loose grit gets 'trapped' and in effect leaves a more coarse finish than desired. (Thought maybe there was some actual microscope pics or something).
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Guess I'm not seeing how the loose grit can 'lap' the top of the blade where the burr is forming. I can (in theory) see it affecting the very edge, where loose grit gets 'trapped' and in effect leaves a more coarse finish than desired. (Thought maybe there was some actual microscope pics or something).
Man, you'd need a sled on an abrasive and a real good camera....
The burr starts out as steel at the contact area along the edge - neither up nor down. It is the last bits of steel on the upside bevel as the abrasive underneath has been ground off. Some of it is steel that has been yanked on (trailing pass) and some has been pushed up as it deflects away from the abrasive colliding with the edge (leading pass). Heavy pressure will actually push the edge over and it will begin to look like the tip of an elf's shoe.
Pressure is what pushes it up. Less plowing depth or weaker anchor on the plow when trailing, or less anchor on the leading pass allow the abrasive to shift out of position = smaller burr. Some of the loose grit will just roll around under the bevel. You can see evidence of this happening as the steel will have a frosted finish, especially at the shoulder border where the trapping pressure lets off.
The lapping action reduces it from forming, doesn't really help with the push up component. Also makes it real easy to eliminate the burr with a leading pass, but the challenge of making a crisp edge comes in.
I don't think I can get pics of this effect in a progression - not sure how I'd isolate the variables, maybe Todd (Science of Sharp) can or already has.
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"A sled"?? Hahaha... I mean pics of an edge after sharpened on a stone with and without slurry (but still has a burr)... to see if there's a difference. I looked at SoS... didn't see anything along this line... but will check again. I know there's a difference in the burr created edge leading vs. edge trailing... just not sure about the 'slurry affect'.
I'll play around with this one of these days... see if I can tell a difference.
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Cbwx,
The apex of the edge directly ploughs into the slurry--which contains loose abrasive particles released from the stone--on each edge leading pass. This is expected to have the effect of slightly rounding over the apex as you sharpen, but at the same time to reduce burr formation by abrading any burr that begins to form at the apex.
Plus, if you use very muddy waterstones and flatten them immediately prior to use, it is easy to develop such a thick layer of mud on the surface of the stone that it visibly comes up and over the top side of the edge as you make edge leading passes. Creating a thick slurry on the stone is actually why I always flatten my waterstones immediately prior to use and never after.
OP I believe I know who wrote that about the burr . I'll say this I used to read pretty much everything that guy put out and I believed it too.
Thing is I started having very different results from him on some stones and some of the things he said I just couldn't agree with just remember charts and graphs and microscopes and 3 pages with big words doesn't make you the be all end all when it comes to sharp edges .
The guy knows what he's talking about for the most part but some things I just can't get on board with about him.
If it's the same guy he questioned Heavy_Handed and debated him and heavy_handed held his own and supplied evidence of his opinion which contradicted the other guys but in the end I believe heavy_handed knew what he was talking about .
As far as the burr goes even if your sharpening with a western strole your still going to get a small amount of a burr .
I firmly believe if you don't sharpen to a burr you aren't really sharpening but more less honing . Not to say you need a gigantic burr but you do need to know that that edge has rolled over . Just my opinion based on my results and sorry but I have no fancy graphs to back it up.
Thing is I started having very different results from him on some stones and some of the things he said I just couldn't agree with just remember charts and graphs and microscopes and 3 pages with big words doesn't make you the be all end all when it comes to sharp edges .
The guy knows what he's talking about for the most part but some things I just can't get on board with about him.
If it's the same guy he questioned Heavy_Handed and debated him and heavy_handed held his own and supplied evidence of his opinion which contradicted the other guys but in the end I believe heavy_handed knew what he was talking about .
As far as the burr goes even if your sharpening with a western strole your still going to get a small amount of a burr .
I firmly believe if you don't sharpen to a burr you aren't really sharpening but more less honing . Not to say you need a gigantic burr but you do need to know that that edge has rolled over . Just my opinion based on my results and sorry but I have no fancy graphs to back it up.
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Hey thanks for the reply. Here's why I don't get it... maybe you (or someone) could explain the difference. What seems to be the theory is the edge is "plowing" into this slurry, which abrades the edge and keeps the burr from forming. But if I sharpened on a really coarse stone, with no slurry... I'd still have the edge "plowing" into these coarse abrasives sticking up, and yet a burr readily forms. So, what difference am I missing?
pjwoolw
Sharpening guy
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This subject of burrs is more often than not over thought. Regardless of the technique and media used a burr of some sort is going to form. The real trick is to create the burr so its easy to remove at the appropriate moment. That comes with experience and what works for the individual using the tools at hand. If your using anything harder than cork to remove a burr your technique needs to be adjusted. If your using a piece of wood the steel is really crappy or your technique is lacking. Now I've been there done that as I sharpen allot of knives on a weekly basis. I don't get to pick what I sharpen so I have to adapt to the items I'm given. No one method works for everything. There are to many variables to account for. No magic bullet. Well sometimes there is.
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What are the things that you don't agree with? He tend to regard any bending of the steel as bad for edge retention and meticulously seek to minimize it. What are your thoughts on his method of "de-stressing" the edge by grinding away the apex (weakened steel according to him) on a stone before each sharpening. Will it make a noticeable difference in edge retention for a knife that's just normally dulled in use? Does normal grinding not remove enough steel at the apex compared to this method?
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Making a burr produces a sharper edge consistently.
People just have a hard time with burr removing
Sometimes it takes multiple techniques
Fatigued metal? Idk sounds like poor burr removing.
You have to make a burr if you want the sharpest edge.
Honing will only do so much.
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That's a vendor image (via Amazon) of the type of USB microscope I have. Rated up to 200X magnification, 2 megapixels (1600 x 1200) resolution. The end-result pics are pretty decent, but it's kind of tedious to set up and get the lighting where I want it (the scope has coaxial LED lighting, adjustable brightness, projects from the 'tube' body of the camera). I often rely more on an external light source, like a lamp, to better manipulate the lighting. The adjustable base seen in the pic is handy, but has a little too much play/wobble when making adjustments for focus or lighting or whatever; keeps moving off-position when adjusting it, so it's slow to get it just right. I haven't used it very often, due to the tedious nature of setting it up. Depending on what software is used to interface it with your computer, it may or may not be easier to deal with. But, once in a while, the subject of the pics makes all that hassle a little more tolerable.
( Sorry for the oversized vendor pic; it was the only one I found in looking for a quick pic of it on the web. )
David
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I think the more important point is the looseness of the abrasive which prevents fixed particles to roll the steel at the edge when hitting as in a very hard stone, besides the slurry abrades the little bits that actually got rolled over.
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The difference is the mobility of the abrasive particles. The burr is a result of the abrasive catching onto the steel and pushing some out of whack as it scrapes material away. Grinding action is basically scraping material away (aside from CbN if properly aligned is more of a tooling action). When it scrapes, it forms a wake at the lead edge and the sides of the abrasive, whether it is leading or trailing - though trailing will make a more pronounced burr faster. This wake is what forms the burr.
As the abrasive becomes more and more loose, it catches and digs less. Some of the abrasives will slide between the workpiece and the stone, some will tumble. The burr that forms as the steel is pushed past its ability to resist, becomes smaller - with a hard fixed abrasive the abrasive wins out and the wake is going to be determined by the properties of the steel and how much pressure the abrasive has behind it. With a more mobile abrasive the furrow might generate enough resistance the abrasive shifts before the burr reaches the same size - now the wake is influenced in some part by the properties of the binder the abrasive sits in, or the texture of the surface the abrasive is resting on.
When the abrasives are more free to roll, slide and tumble the conditions that lead to burring are greatly reduced. As you get closer to lapping you might have no burr form. I also noticed on some stones intended for different industrial sharpening applications, the binder was so soft the edge would barely form a burr even with a fair amount of force on a trailing pass. Many softer waterstones fall into this category and almost have to be used with a trailing pass to get good results. Loose grit on a hardwood knifeboard is the same principle - you can grind with a scrub or a leading pass, but to clean up the edge it had to be finished with a trailing pass.
Same steel, same stone, first pic with slurry, second is no slurry. You can see in the slurry image almost no trace of the track marks stopping in mid grind, the average depth is less.
This is a micrograph of an edge done with a muddy 1K and finished with a few passes at slightly higher angle on an 8k polishing stone. You can see the pitted frosty appearance of the 1k. To the naked eye it just looks like a frosted scratch pattern with microbevel.
Silicon Carbide stone with oil/mud:
India stone:
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I'll add to this, I personally do not see any point in the act of "destressing" an edge unless one knows the thing is low RC steel that has been burnished many times or worked hard to a burr (usage so aggressive the edge was turned instead of being dulled). Most edges are dull - the steel that used to form the edge has been abraded away far more gently than any abrasive will manage. So unless the edge is drawn out or beaten to what appears to be an existing burr, why bother?
Otherwise the steel isn't going to be fatigued by use anymore than it would be by the initial face grinding resulting from the act of destressing in the first place.
As for sharpening without creating a burr - technically possible or one wouldn't be able to cleanly remove the burr either. Question is whether it is easier, more reliable etc - in short, is there is a good reason to do so and I don't believe this to be the case.
Sharpening to a burr is fast and thorough. One can use tactile aids throughout - three finger sticky, lateral rub etc - no need to rely so much on visual cues. The forces that caused the steel to burr are going to be present in burrless methods as well - a percentage of the subsurface steel being dislocated by the abrasive where it hasn't been cleanly sheared away. In the case of destressing with coarse or medium grit I'd expect a greater depth of this to be happening as well. And the likelihood of creating a small burr anyway at least in some spots along the edge will always be present, might as well just get on with it and get as efficient at deburring as possible.
Brent Beach has an interesting read on this topic - his take makes far more sense to me but I've never noticed a difference in longevity all else being equal.
His stuff is well researched and he qualifies his conclusions without making many blanket statements. The whole site is a good read, this is the page I'm referring to:
http://www3.telus.net/BrentBeach/Sharpen/jig faq 02.html#thebest
Otherwise the steel isn't going to be fatigued by use anymore than it would be by the initial face grinding resulting from the act of destressing in the first place.
As for sharpening without creating a burr - technically possible or one wouldn't be able to cleanly remove the burr either. Question is whether it is easier, more reliable etc - in short, is there is a good reason to do so and I don't believe this to be the case.
Sharpening to a burr is fast and thorough. One can use tactile aids throughout - three finger sticky, lateral rub etc - no need to rely so much on visual cues. The forces that caused the steel to burr are going to be present in burrless methods as well - a percentage of the subsurface steel being dislocated by the abrasive where it hasn't been cleanly sheared away. In the case of destressing with coarse or medium grit I'd expect a greater depth of this to be happening as well. And the likelihood of creating a small burr anyway at least in some spots along the edge will always be present, might as well just get on with it and get as efficient at deburring as possible.
Brent Beach has an interesting read on this topic - his take makes far more sense to me but I've never noticed a difference in longevity all else being equal.
His stuff is well researched and he qualifies his conclusions without making many blanket statements. The whole site is a good read, this is the page I'm referring to:
http://www3.telus.net/BrentBeach/Sharpen/jig faq 02.html#thebest
My main disagreements with the guy are his results with waterstones . Certain stones don't cut your higher end steels as well as others and my experience is basically the complete opposite of his .
He says it's OK to put oil on water stones .
I'm a member of his forum . I used to try his process of sharpening and it worked . I used to "destress" and all that and the only difference I found is time sharpening .
Destress vs grinding to a burr is basically the same thing . He cuts the cutting edge off by what the straight razor community calls bread knifing .
Most other people get down to fresh steel by doing passes on a stone .
Main disagreement is about stones and the biggest is his views on the naniwa aotoshi (green brick of joy 2k) I find the stone likes carbon or lower end stainless steels and it will polish up to about 4k if you let it load etc. It's a weird stone and you can get a great polish off the stone if you play with it .
The other guys swears you can't get a good edge off the stone because it's so muddy . I disagree and I've seen pics of how muddy his stone gets and my stone doesn't produce near as much mud , I think he's using way too much pressure on that stone because I've never seen anyone use the green brick and have THAT much mud . He also claims the green brick cuts 10v the same as a 400 grit superstone. Again my results with the stone are more less what the stone is rated at 2k . Then if you let the stone load or play with the mud you can get around a 4k polish but 400 grit ? No way . I've had the stone for years even recommended it to the guy to try and I dunno just completely different results .
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