Burrs and Steel

knifenut1013 said:
It was not in any way ment as an insult, I just don't see the advantages in making a knife duller before sharpening or how it would help the burr that is created by the sharpening process.
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Sorry for the misunderstanding, but I find that dulling out the edge actually prevents me from creating the sharpening burr in the first place, espescially on edges that had seen very heavy use that can be tough on a knife.

Mike
 
Here we see 2 different approaches to the same problem. Knifenut prefers to form a burr, and doesnt really appear to worry about how big it is, then removes it by whatever method has proven successful. Depending on how big a burr Knifenut forms before removal, he may very well get past the damaged metal at the end and not have to worry about damaged/fatigued metal making a burr more difficult to remove. Also, diamond, which Knifenut uses in later steps, removes difficult burrs very well, as it cuts with less pressure and that allows burrs to be removed without bending the edge over to form another.

Gunmike prefers to minimize the burr and thus have to use less effort to remove it later. Part of minimizing burr formation is removing any metal that has rolled or dented, however microscopically, as this metal appears to flop back and forth and require more effort to remove later. I know I saw this in play on the old kitchen knives mentioned above. Another part is making sure that the entire edge has the same starting point, so the same amount of removal effort works the same along the entire edge. These last 2 goals are accomplished by cutting lightly into the stone. I use this step on soft steels that are prone to forming a burr that is difficult to remove, even without the edge being fatigued or deformed. Knifenut doesnt need this step because his burr removal technique is different.

The goal in all of this is a sharp burr free edge, we just see 2 different ways to get there. For what its worth, knives can be sharpened without forming a burr in the first place, and this seems to be what gunmike is leaning toward.
 
matt321 said:
Some burrs are crumbly and wire-like. They can be cleaned off by using very light, cleaning strokes on the stones for the last few rounds. Also, increasing the angle and using light strokes works. Another method is to run the edge lightly through soft wood. I once saw a burr like this get raked off by making a gentle stroke on the corner of a SharpMaker rod. You could see the thing peel off.

Other burrs are more deeply rooted and tenacious. Instead of a nearly detached, wire like burr, these are more like the edge is just curled at the microscopic level. This type is more problematic and is what I usually get on the SharpMaker. I think the back-and-forth action of the SharpMaker tends to limit burr formation except for this type. Using heavy strokes encourages these to form. Once they form, they won't go away. They just flop back and forth when you try and remove them. You either just align the thing straight with the edge and live with it, or you cut it away by making direct perpendicular cuts into the stone (light pressure) to square off the edge in preparation for your next attempt at forming a clean edge. 420HC behaves this way on the SharpMaker for me. I can't make it go away once it forms. I use very light pressure to avoid these. Another strategy is to start by using diamond stones to form a clean bevel intersection and then use the ceramic rods to refine and polish. The diamond abrasives cut more cleanly whereas the ceramics tend to push metal around more blunt like.
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Just for the record: I agree with pretty much everything in this post and while I don't really disagree with post #7, I think it is pretty incomplete. Some people have shown many times how sharp a coarse finish can be. If I had to name a person I would be Sodak, who recently has posted a shaving edge from a bastard file. The reason why most people don't achieve this level of sharpness from a coarse medium is the burr. But as these practices show, a fine abrasive is not necessarily needed to deal with that burr and very few people rarely optimize sharpness at a given grit level. The first picture in post #7 simply shows an incompletely honed edge. It also goes against what Verhoeven has shown in several of his works, were you can clearly see the deformed and rolled burr, even at a fine grit finish. While it is certainly easier to reduce burr formation at a high grit finish it is absolutely no guarantee that you completely remove the burr.

There is also no doubt that the steel has an influence on the way it sharpens. There are steels that feel rubbery that form large and floppy burrs and other steels that tend to form much smaller burrs. In my experience, the tendency of burr formation is strongly dependent on the amount of free Cr. This refers of course to steels at the commonly available hardnesses. Larrin has pointed out that the tendency of burr formation of steels like 420HC is probably due to a suboptimal hardness. Considering the reports of the performance of Phil Wilsons knives in 420HC this seems likely, but I have no personal experience with them.

Finally cutting efficiency is also clearly a factor in burr formation. Abrasives such as SiC and Diamond are much cleaner cutting, leaving a smaller burr than other abrasives, in particular ceramic. In the sintering process the particles are rounded and don't cut as aggressively anymore. Cutting efficiency is especially noticeable with steels that have a large carbide fraction, were abrasive hardness plays a role as well.
 
My ears are burning! Thanks for the compliment HoB, but that wasn't me! I wouldn't want to steal any of hardheart's thunder! ;)

I have gone both ways on burr formation, for the really soft steels, I prefer Gunmike's technique. For whatever reason, the softer steels are hard for me to sharpen, and when cutting, I seem to weaken the edge (I'm heavy handed sometimes). By cutting directly into the stone lightly, I get rid of all the weak stuff. I've quit steeling my knives for that very reason, it seems like it just weakens the metal too much for edge retention. No matter which steel and hardness you are using, once you bend and rebend steel, you've weakened it. Period.

Ironically, for me, the "hard to sharpen" steels, are the easiest. M2 at 66 HRC, ZDP, etc. They tend to form little or no burrs when I sharpen.

But most of you already know this - I have to say, it's fun reading this thread, most of the serious sharpening folks have been contributing here!
 
me2, I do pay attention to the burr but I don't worrie about it until my last few strokes on the stone. The burr is just something that happens when your two bevels meet, if your not forming a burr then your not bringing your two bevels together or your superhuman and can hold perfect angles and pressure. As you sharpen the bevel contacting the abrasive becomes more acute in angle and the other side becomes more obtuse. Now if you think about this you have just removed the edge at the point the angles meet and must sharpen the other side to equal the angles and bring the edge back to center. Remember this is all happening on a microscopic level. When your two angles are almost perfect the burr will be reduced to almost nothing at this point you can either stop or move on to your next finer abrasive.


HoB, The picture I posted shows the burr reduced as much as possiable with my ceramic stone. I can get less of a burr by using my XX-fine DMT but its also not as sharp as with the ceramic. I also don't try and remove all of the burr with my last stone, not on purpose but because I am using more abrasives after that. I reduce it as much as possiable then move on to my strops with several different diamond abrasives. I also don't think of my finishing steps as stropping, I think of all the steps as sharpening.

The ability to sharpen a knife with a coarse stone or file to shaving sharpness is all in the ability of the one doing the sharpening. I can get a shaving edge from my DMT X-coarse and have almost no visible burr but this does not mean that it can't get sharper or that I am happy with it.

Sharpening is sharpening no matter how you look at it, its just bringing two angles together at their finest point.
 
hardheart said:
really?:)
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Ouch....:(. Well really, when it comes to XXXXX course shaving edges it's a 50/50 chance one of you two is responsible :).

But....damn,....my memory is fading if I can't keep you two apart. I am truly embarrassed :(
 
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LOL! I'm honored to be mentioned in the same sentence as hardheart - no worries! :D
 
It doesn't take superhuman powers to get good sharpness without forming burrs, just lots of practice sharpening and seeing with your microscope what is happening with the edge. For instance, I know my Krein CPM M4 Ultimate Caper should be tree topping nicely and starting to whittle hair at DMT fine before a burr starts to form. My CPM D2 Millie and other crisp steeled knives will easily do that at Spyderco medium or Shapton 1000. As you progress grits just look for it to hit certain milestones of sharpness at each grit and you can see the scratches from each grit approach the very edge. When I do form a tiny burr I basically have to go backwards in sharpness by raising the angle to remove the burr. As others have noted there are steels like CRKT's AUS-6 and S&W's 440C that are underhardened and they form burrs so bad that I have to cut straight into a stone to remove the burr and start over. The strop can be the great equalizer, because it can remove the last hints of a burr if you did a good job sharpening. However if you have a big floppy burr and rely on the strop you may be in for a ragged edge after the burr rips off. After my sharpening experience, especially before I got into stropping I hated forming a burr to begin with because all I could do to get rid of even a tiny burr was to raise the angle to remove it. I guess it was then that my no burr philosophy started. Either way works as long as at the end you have a sharp edge with no burr.

Also, Hardheart's bastard file work shows that burr free edges are easily attainable with skill at coarse grits. My DMT XX Coarse edges shave and push cut newsprint, and I think setting that sharp baseline with the coarsest stones sets the foundation for the sharpest possible polished edges.

Mike
 
for Edge Pro owners, Ben Dale mentioned getting a perfect edge, one formed without creating a burr, in the literature that came with the sharpener. At first I thought it was crazy, but now I just use a light touch.
 
sodak said:
Ironically, for me, the "hard to sharpen" steels, are the easiest. M2 at 66 HRC, ZDP, etc. They tend to form little or no burrs when I sharpen.
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Kind of a corollary to that ... the one good thing I'll say about steels that tend to form large and/or stubborn burrs is that at least it's a good indication that edge retention won't be very good, even if you go through all the machinations needed to get a clean edge; ergo, you're probably wasting your time. Perhaps this makes me something of a steel snob, but I just don't see any point anymore in screwing around with blades that don't sharpen cleanly, like you point out.
 
New idea (for me anyway); when you have an edge that is newly honed and sharp, lightly run the blade edge across the edge of a credit card. It's giving me a sharper edge, I guess by cleaning off micro-burring. (I don't have a microscope to look and see)
 
matt321 said:
New idea (for me anyway); when you have an edge that is newly honed and sharp, lightly run the blade edge across the edge of a credit card. It's giving me a sharper edge, I guess by cleaning off micro-burring. (I don't have a microscope to look and see)
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Perpendicular, or an edge trailing stroke? Interesting idea!
 
Perpendicular.
I just started testing this, but it seems to add a few percent under the right circumstances. I think it is just another version of the strategy of removing some burrs by cutting lightly into wood.
 
My DMT XX Coarse edges shave and push cut newsprint, and I think setting that sharp baseline with the coarsest stones sets the foundation for the sharpest possible polished edges.
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Shave maybe but push cut newsprint is a little far fetched. The edge left by a diamond stone of that coarseness is not even a edge but more like chipped metal. The final stone used is the one that really determines the sharpness of your final edge along with the micron gap between your final stone and the polish compound and type of compound.

http://mse.iastate.edu/fileadmin/www.mse.iastate.edu/static/files/verhoeven/KnifeShExps.pdf
 
knifenut1013 said:
Shave maybe but push cut newsprint is a little far fetched. The edge left by a diamond stone of that coarseness is not even a edge but more like chipped metal. The final stone used is the one that really determines the sharpness of your final edge along with the micron gap between your final stone and the polish compound and type of compound.

http://mse.iastate.edu/fileadmin/www.mse.iastate.edu/static/files/verhoeven/KnifeShExps.pdf
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OK you are right and I'm full of crap. Take your links and keep on reading them (I'm on my iPhone and can't read it now but guessing I've already read it). I haven't tested push cutting newsprint on a DMT XX Coarse edge in ages, but I remember pushcutting it right at the point of hold. Did I use a tiny bit of draw to get it started, maybe, but I don't think so. Either way, I don't need the internet to boost my ego, I am just trying to exchange ideas and experiences on sharpening. At this point I don't really care about your opinion of what I say. I guess I can't pushcut newsprint well over 4" from the point of hold because you say it's farfetched. I am done with this thread. And yes, I know how rough a DMT XX Coarse edge is. I formed them all the time when rebeveling knives before my back surgery, and will do so more after my back surgery.

Mike

Mike
 
Sorry you are taking everything I say to heart but everything you are saying goes aginst what is known about the formation of a edge. I am just trying to help here sence it seems that the facts of sharpening have been lost a little with all this bickering.
 
knifenut1013 said:
Sorry you are taking everything I say to heart but everything you are saying goes aginst what is known about the formation of a edge. I am just trying to help here sence it seems that the facts of sharpening have been lost a little with all this bickering.
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Well, sometimes your "facts" are not borne out by real world results. If you feel I am an Internet blow hard fine, but as I have said several times I am just sharing my experiences with everyone, as factually as I can. If my techniques and results don't agree with your facts I don't know what to say to you. Apparently you think only your way works, where I know for a fact there are many different ways to achieve a very sharp edge. Go tell Tom Krein that his 120 grit edges that tree top arm hairs and push cut newsprint well away from the point of hold aren't possible because of an Internet link. The reason I take you posts personally is because of your choice of words when quoting and disagreeing with me. Oh yeah, as Hardheart said, go tell Ben Dale of Edge Pro fame that he is full of it by calling the perfect edge a burr free edge. Anyway, if you obviously are an excellent sharpener, I just think you are being closed minded by being so dismissive of the sharpening techniques of others. This forum is a good place to share sharpening ideas and techniques so we can learn from each other, but you just seem to dismiss any technique that doesn't agree with your's in rude terms ("pointless" and "far fetched" are terms I consider rude). You seem to have your head stuck in the theoretical world where I am just telling my real life experiences from using many different techniques to find what works for me. If it disagrees with your ideas of how an edge forms then I guess either I'm full of crap or the sharpening world isn't as cut and dried as you think it is.

Mike
 
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