Luftmensch
Senior Member
- Joined
- Dec 13, 2017
- Messages
- 2,316
- Reaction score
- 3,186
Good Scientific Resource?
- Thread starter Tea_Hills
- Start date
Help Support Kitchen Knife Forums:
I think the fact that the scratches on the bevel don’t end in teeth, but rather irregular hills and valleys, points to this.
Luftmensch
Senior Member
- Joined
- Dec 13, 2017
- Messages
- 2,316
- Reaction score
- 3,186
In the context of what I understand the machine definition of 'break out'... or negative burr to be. I would prefer to use the term tear-burr or tear out if you are talking about chips on the edge... I know it is nitpicking...
In the context of what I understand the machine definition of 'break out'... or negative burr to be. I would prefer to use the term tear-burr or tear out if you are talking about chips on the edge... I know it is nitpicking...
Can you explain the difference better?
I would prefer to use the term tear-burr or tear out if you are talking about chips on the edge... I know it is nitpicking...
I agree. Tear-out, chip-out, or break-out all make more sense to me. Separate from this is the question of how to identify and deal with it.
I think he’s making a distinction between break out and tear out. I’m just not sure what the difference is to him.
I tend to agree with @Luftmensch, I am not convinced what happens in machining is what happens when hand sharpening. The cutter usually moves in one direction, is this correct? When hand sharpening most alternate between edge leading to edge following. With edge leading what happens to the apex seems different. The ridges and valleys on the apex might be results of weakend burr breaking off unevenly or even collision with hard abrasive particles.
I've got the answer, just not sure if OP is referring to a horizontal negative burr or a vertical one?
There are some things to consider. First, he does a lot of machine sharpening, but I'm gonna skip that, even if I know some things about it. I will address more the jig and unidirectional sharpening that some guys do (so even with freehand). I know people that with jigs move only one way and never against the edge. Is their experience that this would simply tear the apex of some alloys, never getting a burr. It's not a tear with/of a burr that would pull the entire thing uneven. Note that they use only diamond and/or cbn and also note that in the above mentioned machine sharpening, cbn is common. This being said, it was shown that with enough force, similar behaviour is possible with other abrasives. He does say at some point that there is a difference between how diamond/cbn vs. regular stone abrasives interact with the structures and even when a burr happens, it's of different nature. This is a point where our experience is similar. Again, this is not a given, as force and consistency can change what's happening. And most people here get at least cleaner edges faster with various diamond surfaces (if not better altogether and most say they do) - cbn is less common in usage, as far as I could tell, because it's less available.
As a side note, the break can happen even if it's not against the edge, but seems to be less frequent.
BoSharpens
Well-Known Member
Funny stuff. I've sharpened for decades, get good results, have a microscope to check edges at times to see what I'm getting in. I manage to get rid of burrs with diamond laps and a leather strop. The edges are then very sharp and cut very nicely. That's what I want.
Will discussions of positive and negative burrs make a difference in anyone's technique?
Will discussions of positive and negative burrs make a difference in anyone's technique?
We discuss stuff that makes no difference all the time. That said can't beat practice when sharpening for sure. Even with jigs and equipment still need practice to build the skills.
The whole negative burr stuff though
The whole negative burr stuff though
KilgoreTrout
Banned
Do you have links to the videos?
You could use the same logic to dismiss any innovation in sharpening, though. It’s great if you’re happy with your technique, but it’s also fine if people want to probe some other avenue, informed by some sort of new understanding of the mechanics of abrasion. That’s what this discussion aspires to be, at least. I’m still not sure if it is that or not. The positive/negative business confuses me. It also seems like the practical recommendations that the people promoting this viewpoint make are essentially what many of us do anyway: raise the angle for stubborn burrs.
Didn't know they were tournedos, just grilled and ate them steaks.
Luftmensch
Senior Member
- Joined
- Dec 13, 2017
- Messages
- 2,316
- Reaction score
- 3,186
Caveat emptor... "Vell, Luftmensch's just zis guy, you know?"
I barely know what the difference is to me!
So just to recap. The conversation went down this path and I seem to have backed myself into a corner
'Negative burrs' are a new concept to me. When I asked for an explanation, an example from machining was presented. I have no problems with this definition... I am just uncomfortable applying that example to whetstone sharpening.
As far as I can tell from the figure and some reading, negative burrs occur during break out. In a brittle material, as a cutter approaches the end of the workpiece, less and less material is available to support the cutting forces. Eventually the cutter will reach a distance from the end of the workpiece where deformation between the cutter and the unsupported material will occur. The cutter is pushing material diagonally upwards... away from the stock material and towards the unsupported end. This creates a 'pivot' point in the material. The unsupported end of the pivot is in compression and the interface at the cutter is in tension. The cutter is also spinning and appling a shear force to the material at the interface between the blades and the material. The stress in this region may cause a crack - perhaps around some flaw in the material or an extreme concentration point (maybe chips/swarf that aren't properly cleared away). Once the crack forms it propagates quickly along deformed region which is already under strain. The crack reaches the end of the workpiece before the cutter is able to finish the pass. This causes 'break out' - the chip is broken off rather than being cleanly cut.
Feed speeds, spindle RPM, depth of cut, number of teeth on the cutting tool... rake angle... etc... these will affect how much break out occurs.
I do not believe it makes sense to apply machining break out to honing. I am not sure what the analogy would look like? I created a figure to try and illustrate break out (top row):
Tear out is very similar (bottom row). Rather than being cut cleanly... unsupported material fails in the direction of the cut. Once abrasion reaches the very edge, there is very little supporting material. A tiny amount of edge material will be placed under tension (as a simplification) from the abrasion. The material is brittle (hard) and resists deformation, so it does not bend out of the way. Eventually stresses in the remaining supporting material exceed the fracture strength... since the material is brittle, this is likely close to the ultimate tensile strength. Brittle fracture occurs. To me this is a more compelling explanation.
In both scenarios, the cut is not finished cleanly. The material fails before the cut can exit the material cleanly. The difference is in how they fail:
I don't believe there is a need for the term 'negative burr'... but if there had to be... explaining it with tear out burrs would make more sense to me than break out burrs
Identification?? I don't know... you are talking about the limits of human perception (if you don't have fancy equipment). Assuming you don't have a big, flappy, ductile burr... something will be happening at the edge of the steel. Lets say your eyes can resolve objects at 40 micrometers. Maybe you will be able to see something at JIS 400. Perhaps you can use other tricks (reflected light... fingers) to sense higher grits.
But I dont know that you need to identify anything if you do not have a big, flappy, ducticle burr. The recommendation to 'deburr' at the same apex angle just sounds like polishing to me... Dont get me wrong... this is sensible!!! But is it really any different to saying 'polished edges are more durable'? As you progress through your sharpening, finer stones and lighter pressure will help clean up a ragged edge. Your edge will always be ragged and stressed at some level of magnification... just make those regions smaller and smaller until the macro geometry suits your purposes.
I barely know what the difference is to me!
So just to recap. The conversation went down this path and I seem to have backed myself into a corner
'Negative burrs' are a new concept to me. When I asked for an explanation, an example from machining was presented. I have no problems with this definition... I am just uncomfortable applying that example to whetstone sharpening.As far as I can tell from the figure and some reading, negative burrs occur during break out. In a brittle material, as a cutter approaches the end of the workpiece, less and less material is available to support the cutting forces. Eventually the cutter will reach a distance from the end of the workpiece where deformation between the cutter and the unsupported material will occur. The cutter is pushing material diagonally upwards... away from the stock material and towards the unsupported end. This creates a 'pivot' point in the material. The unsupported end of the pivot is in compression and the interface at the cutter is in tension. The cutter is also spinning and appling a shear force to the material at the interface between the blades and the material. The stress in this region may cause a crack - perhaps around some flaw in the material or an extreme concentration point (maybe chips/swarf that aren't properly cleared away). Once the crack forms it propagates quickly along deformed region which is already under strain. The crack reaches the end of the workpiece before the cutter is able to finish the pass. This causes 'break out' - the chip is broken off rather than being cleanly cut.
Feed speeds, spindle RPM, depth of cut, number of teeth on the cutting tool... rake angle... etc... these will affect how much break out occurs.
I do not believe it makes sense to apply machining break out to honing. I am not sure what the analogy would look like? I created a figure to try and illustrate break out (top row):
Tear out is very similar (bottom row). Rather than being cut cleanly... unsupported material fails in the direction of the cut. Once abrasion reaches the very edge, there is very little supporting material. A tiny amount of edge material will be placed under tension (as a simplification) from the abrasion. The material is brittle (hard) and resists deformation, so it does not bend out of the way. Eventually stresses in the remaining supporting material exceed the fracture strength... since the material is brittle, this is likely close to the ultimate tensile strength. Brittle fracture occurs. To me this is a more compelling explanation.
In both scenarios, the cut is not finished cleanly. The material fails before the cut can exit the material cleanly. The difference is in how they fail:
- Break out: cracks form and propagate (not in the direction of travel) to an unsupported face
- Tear out: material is subjected to high (tensile) forces in the direction of travel, supporting material at the interface experiences brittle fracture
I don't believe there is a need for the term 'negative burr'... but if there had to be... explaining it with tear out burrs would make more sense to me than break out burrs
Identification?? I don't know... you are talking about the limits of human perception (if you don't have fancy equipment). Assuming you don't have a big, flappy, ductile burr... something will be happening at the edge of the steel. Lets say your eyes can resolve objects at 40 micrometers. Maybe you will be able to see something at JIS 400. Perhaps you can use other tricks (reflected light... fingers) to sense higher grits.
But I dont know that you need to identify anything if you do not have a big, flappy, ducticle burr. The recommendation to 'deburr' at the same apex angle just sounds like polishing to me... Dont get me wrong... this is sensible!!! But is it really any different to saying 'polished edges are more durable'? As you progress through your sharpening, finer stones and lighter pressure will help clean up a ragged edge. Your edge will always be ragged and stressed at some level of magnification... just make those regions smaller and smaller until the macro geometry suits your purposes.
Caveat emptor... "Vell, Luftmensch's just zis guy, you know?"
I barely know what the difference is to me!
So just to recap. The conversation went down this path and I seem to have backed myself into a corner
As far as I can tell from the figure and some reading, negative burrs occur during break out. In a brittle material, as a cutter approaches the end of the workpiece, less and less material is available to support the cutting forces. Eventually the cutter will reach a distance from the end of the workpiece where deformation between the cutter and the unsupported material will occur. The cutter is pushing material diagonally upwards... away from the stock material and towards the unsupported end. This creates a 'pivot' point in the material. The unsupported end of the pivot is in compression and the interface at the cutter is in tension. The cutter is also spinning and appling a shear force to the material at the interface between the blades and the material. The stress in this region may cause a crack - perhaps around some flaw in the material or an extreme concentration point (maybe chips/swarf that aren't properly cleared away). Once the crack forms it propagates quickly along deformed region which is already under strain. The crack reaches the end of the workpiece before the cutter is able to finish the pass. This causes 'break out' - the chip is broken off rather than being cleanly cut.
Feed speeds, spindle RPM, depth of cut, number of teeth on the cutting tool... rake angle... etc... these will affect how much break out occurs.
I do not believe it makes sense to apply machining break out to honing. I am not sure what the analogy would look like? I created a figure to try and illustrate break out (top row):
View attachment 160994
Tear out is very similar (bottom row). Rather than being cut cleanly... unsupported material fails in the direction of the cut. Once abrasion reaches the very edge, there is very little supporting material. A tiny amount of edge material will be placed under tension (as a simplification) from the abrasion. The material is brittle (hard) and resists deformation, so it does not bend out of the way. Eventually stresses in the remaining supporting material exceed the fracture strength... since the material is brittle, this is likely close to the ultimate tensile strength. Brittle fracture occurs. To me this is a more compelling explanation.
In both scenarios, the cut is not finished cleanly. The material fails before the cut can exit the material cleanly. The difference is in how they fail:
- Break out: cracks form and propagate (not in the direction of travel) to an unsupported face
- Tear out: material is subjected to high (tensile) forces in the direction of travel, supporting material at the interface experiences brittle fracture
I don't believe there is a need for the term 'negative burr'... but if there had to be... explaining it with tear out burrs would make more sense to me than break out burrs
Identification?? I don't know... you are talking about the limits of human perception (if you don't have fancy equipment). Assuming you don't have a big, flappy, ductile burr... something will be happening at the edge of the steel. Lets say your eyes can resolve objects at 40 micrometers. Maybe you will be able to see something at JIS 400. Perhaps you can use other tricks (reflected light... fingers) to sense higher grits.
But I dont know that you need to identify anything if you do not have a big, flappy, ducticle burr. The recommendation to 'deburr' at the same apex angle just sounds like polishing to me... Dont get me wrong... this is sensible!!! But is it really any different to saying 'polished edges are more durable'? As you progress through your sharpening, finer stones and lighter pressure will help clean up a ragged edge. Your edge will always be ragged and stressed at some level of magnification... just make those regions smaller and smaller until the macro geometry suits your purposes.
Why do you find break out less likely than tear out when stone sharpening?
Luftmensch
Senior Member
- Joined
- Dec 13, 2017
- Messages
- 2,316
- Reaction score
- 3,186
I kind of imagine abrasion is like pulling a rock through sand. The rock will create a groove behind it. It will create berms either side of it as material is pushed aside (its wake if you will). There will also likely be a wave of compressed material accumulating in front of it. If this were on a ledge, once the rock reached the edge, it would push the wave of sand over. If the sand had some cohesion, you would see some tearing effect as the material in berms and beneath the stones attempted to support the wave. As the wave is pushed over the edge it will pull some supporting material with it until the bonds of cohesion fail. You will see raised edges at the berms, a trough from the groove and likely a small amount of drawn out (torn) material... This just seems like a better analogy to me.
Steels are not brittle in the same way that we think of ceramics/glass. Maybe you could cause breakout if you torqued the edge into the stone and applied a lot of force. The edge might just shatter once you reached that point - I doubt it.
But yeah...Tear out... failure in the direction of cutting/abrasion. Break out... failure at an angle to the direction of cutting/abrasion.
I am in the realm of talking out my hoop. It would be easier (for me) if some professor of abrasion came out the woodwork and told me I was wrong and explained why...
Maybe break out and tearout are really the same thing.It is possible with low toughness steel like Aogami Super. I have done it.
If I understand @Luftmensch’s distinction correctly, there’s basically no way you’d be able to tell if you had break out or tear out, though, unless you SEM imaged your blade after or something.
Last edited:
I kind of imagine abrasion is like pulling a rock through sand. The rock will create a groove behind it. It will create berms either side of it as material is pushed aside (its wake if you will). There will also likely be a wave of compressed material accumulating in front of it. If this were on a ledge, once the rock reached the edge, it would push the wave of sand over. If the sand had some cohesion, you would see some tearing effect as the material in berms and beneath the stones attempted to support the wave. As the wave is pushed over the edge it will pull some supporting material with it until the bonds of cohesion fail. You will see raised edges at the berms, a trough from the groove and likely a small amount of drawn out (torn) material... This just seems like a better analogy to me.
Steels are not brittle in the same way that we think of ceramics/glass. Maybe you could cause breakout if you torqued the edge into the stone and applied a lot of force. The edge might just shatter once you reached that point - I doubt it.
But yeah...Tear out... failure in the direction of cutting/abrasion. Break out... failure at an angle to the direction of cutting/abrasion.
I am in the realm of talking out my hoop. It would be easier (for me) if some professor of abrasion came out the woodwork and told me I was wrong and explained why...
The distinction sort of makes sense, although idk why I shouldn’t think of the tear out as a crack happening perpendicular to the cutting direction, which is kinda the same as break out. I’m not sure about the sand analogy though. It’s not so compelling to me when it’s trying to compete against an analogy with milling metal, which I can totally believe is a macro version of sharpening. Maybe macro vs micro makes a difference though.
Luftmensch
Senior Member
- Joined
- Dec 13, 2017
- Messages
- 2,316
- Reaction score
- 3,186
Definitely... we're talking about micrometers... verging on nanometers.
Maybe you should! I am just some guy! After all... fracture in brittle materials under tension will likely start at some weak point and rapidly propagate a crack from there. Both failures will be doing that.
I hadn't actually read this Science of Sharp article. He has some images that look very much the analogy! I had thought of the analogy from other SEM images! Check out this image of a hardened carbon steel coupon. It was polished and then lightly abraded with 600 grit sandpaper:
[Image credit: Science of Sharp]
To what we are discussing... what does the silicon carbide grain do if it reaches the end of the hardened carbon steel coupon? Would it push/pull through the edge and leave a messy exit gouge? Or... if the coupon was thin enough and the steel was hard enough... would it punch through to the opposite face of the coupon before reaching the edge?
If you forced me to guess I would choose messy exit gouge!
Last edited:
Definitely... we're talking about micrometers... verging on nanometers.
Maybe you should! I am just some guy! After all... fracture in brittle materials under tension will likely start at some weak point and rapidly propagate a crack from there. Both failures will be doing that.
I hadn't actually read this Science of Sharp article. He has some images that look very much the analogy! I had thought of the analogy from other SEM images! Check out this image of a hardened carbon steel coupon. It was polished and then lightly abraded with 600 grit sandpaper:
View attachment 161028
[Image credit: Science of Sharp]
To what we are discussing... what does the silicon carbide grain do if it reaches the end of the hardened carbon steel coupon? Would it push/pull through the edge and leave a messy exit gouge? Or... if the coupon was thin enough and the steel was hard enough... would it punch through to the opposite face of the coupon before reaching the edge?
If you forced me to guess I would choose messy exit gouge!
You're right that that picture isn't something you see as much of on the larger cutting scale. Size matters, perhaps.
Mostly true in general. But I imagine people also do a lot of inefficient things, sometimes for scientifically misinformed reasons and sometimes out of habit. It's easy to develop bad habits when you can't actually see what's happening at the edge, and you haven't sharpened the thousands of blades you'd need to in order to notice differences in methods. The things we do work well enough, but the fact that there's constant discussion about various aspects of sharpening, and disagreement among experts, means that perhaps there's something to be gained from further understanding of what's going on.
I totally agree with this.
No, everyone agrees that knives can chip. Luftmensch was trying to theorize about *how* microscopic chips occur in the edge when sharpening on stones; whether they occur via "tear out" or "break out", and whether there's even a difference between those things.
He does. He has different methods for different burr types. For softer steels his method really boils down to:
Creating a burr on a 1000 grit stone at the desired apex angle.
Minimizing the burr size by using a 5 micron or so compound while grinding at the apex angle used on the 1000 grit.
Removing the burr by grinding at a higher angle (about 2 degrees) than what was used to create the apex.
This deburring is done on a felt wheel with .80gm/cm3 hardness.
Cleaning the edge up using the apex angle again and honing on a paper wheel loaded a mix of .25 micron diamond compound and Cr2O3 (Green compound).
For harder steels that would encompass most of the knives we talk about here his process is essentially:
Creating a burr on a 1000 grit stone at the desired apex angle.
Grinding away at the root of the 'negative burr' by using a paper wheel with 5 micron compound at .1 degree lower than the apex angle
Elongating the remaining burr by grinding at apex angle on a .5 micron loaded paper wheel
Removing the final burr by grinding at about a 1 degree higher angle than apex on a paper wheel loaded with 1 micron compound
Cleaning the edge up using the apex angle again and honing on a paper wheel loaded a mix of .25 micron diamond compound and Cr2O3 (Green compound).
When supplies get here I am going to test using a .79gm/cm3 felt strip from durofelt for the felt wheel replacement and a loaded paper strop over the felt block for the paper wheel replacement.
Again, this is entirely for fun. I am well aware it is overkill and unnecessary but I love a good project and in all it was about 100 dollars for the compounds, felt, and "freehand" jig needed to overcome hand sharpening angle variations. My goal is to create and edge that will cut a free hanging hair, which requires and apex thickness of about .1 micron. Will report my findings!
I am in the realm of talking out my hoop. It would be easier (for me) if some professor of abrasion came out the woodwork and told me I was wrong and explained why...
As am I during my research! I'm on the hunt for a abrasion
