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sharpening?
- Thread starter MarkJeffrey
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Er... Yeah, the m4 is sharpened on the Edge Pro with stones, mostly dry.
I disagree entirely that sharpening systems are for the lazy, but I'll agree to disagree.
I disagree entirely that sharpening systems are for the lazy, but I'll agree to disagree.
I guess the million dollar question is, and there are too many variables for there to be any one answer, how deep is the de-tempering?
If it's shallow enough that a quick half dozen swipes on a ceramic hone, strop with compound, or perhaps a high grit waterstone would get you back to sound steel, then that's one thing- if the entire secondary bevel is compromised, then that's another.
I see a fairly dramatic increase in apparent sharpness in going from a 5m belt, around 4500 grit equiv, to an edge lightly honed on a high quality ceramic rod, which is likely to be something like 1800 grit equivalent, and I'm beginning to wonder if removing that tiny amount of compromised steel might account for that.
If it's shallow enough that a quick half dozen swipes on a ceramic hone, strop with compound, or perhaps a high grit waterstone would get you back to sound steel, then that's one thing- if the entire secondary bevel is compromised, then that's another.
I see a fairly dramatic increase in apparent sharpness in going from a 5m belt, around 4500 grit equiv, to an edge lightly honed on a high quality ceramic rod, which is likely to be something like 1800 grit equivalent, and I'm beginning to wonder if removing that tiny amount of compromised steel might account for that.
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Not really. What I'm saying is that you can't assume light pressure and hand speeds are not generating temperatures higher than you'd like. I do not know if the block was scrubbed or just passed one time. There are a couple makers that switched to water cooled diamond stones after hearing Roman's lecture, and noticed a difference.
Now, I sharpen my inexpensive kitchen knives on a Norton Economy stone, and don't make any distinction between using it wet or dry. However, if it were a Murry Carter Gyuto that you expected to do very fine work in a professional setting, it's probably worth thinking about. In the end, a sharp knife is better than a dull one, even if the edge is softened a little in the process.
I have seen some microhardness measurements on power sharpened blades, and they show a definite loss of hardness, dropping as much as 5 points in a very short distance. I'd have to find it again to see the steel used and sharpening method used.
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Wouldn't a manufacturer create a blade/steel in a way that normal sharpening gives the best holding and (insert other desired properties here) edge and thus indirectly take detempering/softening from normal sharpening approaches into account?
Now tricking that by using a less common and not detempering/softening method might produce an edge harder than the manufacturer intended.
Now tricking that by using a less common and not detempering/softening method might produce an edge harder than the manufacturer intended.
Actually manufacturers do take it into account and their answer is to deliver blades with super wide edge angles.
As wisely me2 pointed out we are likely to more appreciate edge strenght the more acute angle we deal with, and to enjoy such kind of edge you also want it to be very fine grained and not saturated by huge box shaped carbides. To really understand sharpening basics we need to think razors.
Extending the basics to knives we reach the pointless when our angles are so wide that talking about "performance" is quickly going out of place anyway.
Ever heard about D2 taking an edge and keep it forever? That "forever" is not related to a sharp and stable edge, not even close...but many are happy with it.
As wisely me2 pointed out we are likely to more appreciate edge strenght the more acute angle we deal with, and to enjoy such kind of edge you also want it to be very fine grained and not saturated by huge box shaped carbides. To really understand sharpening basics we need to think razors.
Extending the basics to knives we reach the pointless when our angles are so wide that talking about "performance" is quickly going out of place anyway.
Ever heard about D2 taking an edge and keep it forever? That "forever" is not related to a sharp and stable edge, not even close...but many are happy with it.
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People keep talking about the "temperature" but no one is talking about the time.
It is time + temperature that matters not one alone
That is why your grinding belts and fingers are not bursting into flames as you grind or sharpen on your 2x72
So do not leave out the time part of the equation.
How long at a certain temperature does it take to decrease the hardness of a blade?
Until you can answer the "Time" part of the equation you will not have an answer
It is time + temperature that matters not one alone
That is why your grinding belts and fingers are not bursting into flames as you grind or sharpen on your 2x72
So do not leave out the time part of the equation.
How long at a certain temperature does it take to decrease the hardness of a blade?
Until you can answer the "Time" part of the equation you will not have an answer
Adam, i have seen micrographs of untempered martensite layer on the skin of a grinded piece of steel... The little time grinding has been enough to austenitize the surface, which has been "quenched" by the steel mass itself. Go figure.
It is not the case that your edge is going to face 200-400 °F for split seconds....it's going more to burn istantly right at the apex.
I don't want to convince you, just i have hard time to concieve spending hours hand sanding high abrasion resistant steel, and rushing in the end to sharpen the thing on the grinder....when NOBODY, since centuries grinds hardened steel without coolant. It's a brand new attitude in the knifemaking world.
It is not the case that your edge is going to face 200-400 °F for split seconds....it's going more to burn istantly right at the apex.
I don't want to convince you, just i have hard time to concieve spending hours hand sanding high abrasion resistant steel, and rushing in the end to sharpen the thing on the grinder....when NOBODY, since centuries grinds hardened steel without coolant. It's a brand new attitude in the knifemaking world.
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Stezann,
And what was the time and temperature as well as pressure was that piece of steel ground at? Also what abrasive was used and what condition was the abrasive, was it new, moderately worn or extremely worn out?
All of those factors need to be revealed for assessment.
And actually it is not a brand new attitude in the knifemaking world and many respected makers whose knives are known to hold an edge from Rudy Ruana to Chris Reeve sharpen without coolant.
Phil Hartsfield knives lacked cosmetic grace and became well known for their ability to cut and hold an edge and no coolant was used in sharpening.
There is a lot of real world evidence produced that a knife if sharpened correctly will hold and edge and perform as expected without coolant being used.
I am not saying using coolant is not a good thing, I am saying it is not necessarily mandatory to produce a great edge that is long lasting if proper methods and abrasives are utilized.
When I did my testing on 2 chisel ground blades of A2 sharpened with and without coolant as both approached 400 cuts of hemp rope I got bored and stopped and it made a huge mess. Both did equally well. 1 blade of each is not enough to prove anything other then both could cut equally well.
If a knifemaker is not going to use fresh new abrasive belt, extremely light pressure or is going to take a long time while sharpening then by all means please use a coolant and go to stones.
As I mentioned before. If a person is concerned about their technique and method dunk your blade into water and monitor the evaporation of the water near the edge as you sharpen, water evaporates a 212 degrees.
And what was the time and temperature as well as pressure was that piece of steel ground at? Also what abrasive was used and what condition was the abrasive, was it new, moderately worn or extremely worn out?
All of those factors need to be revealed for assessment.
And actually it is not a brand new attitude in the knifemaking world and many respected makers whose knives are known to hold an edge from Rudy Ruana to Chris Reeve sharpen without coolant.
Phil Hartsfield knives lacked cosmetic grace and became well known for their ability to cut and hold an edge and no coolant was used in sharpening.
There is a lot of real world evidence produced that a knife if sharpened correctly will hold and edge and perform as expected without coolant being used.
I am not saying using coolant is not a good thing, I am saying it is not necessarily mandatory to produce a great edge that is long lasting if proper methods and abrasives are utilized.
When I did my testing on 2 chisel ground blades of A2 sharpened with and without coolant as both approached 400 cuts of hemp rope I got bored and stopped and it made a huge mess. Both did equally well. 1 blade of each is not enough to prove anything other then both could cut equally well.
If a knifemaker is not going to use fresh new abrasive belt, extremely light pressure or is going to take a long time while sharpening then by all means please use a coolant and go to stones.
As I mentioned before. If a person is concerned about their technique and method dunk your blade into water and monitor the evaporation of the water near the edge as you sharpen, water evaporates a 212 degrees.
Very interesting discussion.
There's a lot of things going on at the same time that are getting thrown into the same box:
-Pyrophoric heat, which produced the spikes in temp seen when rubbing the block of steel over the granite. It's also seen as "proof" that the edge is burning, since sparks are seen during belt sharpening. Not so- I was just watching a video of sparks coming off a water cooled edge. A very high carbon steel can still throw tiny bits that combust when they hit the oxygen, even though the stone is wet.
-Industrial methods and knifemaker methods... granted, many makers are careless at times, but comparing machine shop or factory production methods with what a custom maker does isn't always accurate, since a factory is trying to turn out the maximum amount of work in the minimum time, and will need coolant, since they want to remove all the material as fast as possible- coolant would be mandatory. Knifemakers aren't usually in a hurry like that.
-Careless sharpening in the same box as patient, careful sharpening.
So, you can reach in that box, find a blade that's been ruined, or some high temps, and conclude that all blades done on dry grinders are junk.
And I'm not saying that coolant is a bad idea, (I'm setting up a cooled grinder this week and very excited about having it) just that bad edges on some blades doesn't translate to "All edges done that way are bad."
There's a lot of things going on at the same time that are getting thrown into the same box:
-Pyrophoric heat, which produced the spikes in temp seen when rubbing the block of steel over the granite. It's also seen as "proof" that the edge is burning, since sparks are seen during belt sharpening. Not so- I was just watching a video of sparks coming off a water cooled edge. A very high carbon steel can still throw tiny bits that combust when they hit the oxygen, even though the stone is wet.
-Industrial methods and knifemaker methods... granted, many makers are careless at times, but comparing machine shop or factory production methods with what a custom maker does isn't always accurate, since a factory is trying to turn out the maximum amount of work in the minimum time, and will need coolant, since they want to remove all the material as fast as possible- coolant would be mandatory. Knifemakers aren't usually in a hurry like that.
-Careless sharpening in the same box as patient, careful sharpening.
So, you can reach in that box, find a blade that's been ruined, or some high temps, and conclude that all blades done on dry grinders are junk.
And I'm not saying that coolant is a bad idea, (I'm setting up a cooled grinder this week and very excited about having it) just that bad edges on some blades doesn't translate to "All edges done that way are bad."
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From Mr Landes.....
"Grinding generates energy (heat) and every step of sharpening is grinding even the strop. This heat can be sucked away by the right coolant such as water. If the grinding action lacks the coolant, the heat goes mostly into the torn out part and the body (blade/edge) it was torn off. It becomes obvious to see the induced energy when you see the sparks fly (Burning steel!!). Depending on how hard you go over the piece the more energy is induced the hotter it gets, thats basic physics.Than the guys come and say but I can do it so sensitive that the edge will not suffer and I'm dipping the blade each run into cold water....Well that is a nice effort, but when it comes down to the very edge this tiny fraction is overheated faster, than the eye can see or the wrinkled fingers can feel. Unfortunately the edge becomes thinner the close you come to the very edge/point means generated heat will get jammed in the tip.
In addition to that tempering colors that would visually proof this are ground away immediately when they appear and Stainless steels need a higher temperature to generate tempering colors and longer time to build them up.
Nevertheless one can do metallurgical examination that can proof the issue testing micro hardness. There are some old german study's that examined this issue in the very detail."
"I had a book dedicated to general grinding methods, in this book i found a test application. A normal steel block apx. 2"x2"x4" that had a large number of highly sensitive thermocouples integrated in the surface. The block was slit dry by hand over a 1000grit grinding paper. The peak temps measured, walked up to 2000°C for split seconds in the very surface (some microns). Of course the block did not melt since the volume fraction of induced heat was to tiny to affect such a large solid piece of steel. But the effect was there and proofen. In a edge we just talk about some microns of material, here the effect is solid an clear. Every manufacturer of razorblades knows this and does excessive cooling whilst grinding and polishing edges, that need to hold an super sharp edge for very long. It seems just some the magic makers out of the custom knife scene think, the physical principles like this, do not apply to them...."
"Grinding generates energy (heat) and every step of sharpening is grinding even the strop. This heat can be sucked away by the right coolant such as water. If the grinding action lacks the coolant, the heat goes mostly into the torn out part and the body (blade/edge) it was torn off. It becomes obvious to see the induced energy when you see the sparks fly (Burning steel!!). Depending on how hard you go over the piece the more energy is induced the hotter it gets, thats basic physics.Than the guys come and say but I can do it so sensitive that the edge will not suffer and I'm dipping the blade each run into cold water....Well that is a nice effort, but when it comes down to the very edge this tiny fraction is overheated faster, than the eye can see or the wrinkled fingers can feel. Unfortunately the edge becomes thinner the close you come to the very edge/point means generated heat will get jammed in the tip.
In addition to that tempering colors that would visually proof this are ground away immediately when they appear and Stainless steels need a higher temperature to generate tempering colors and longer time to build them up.
Nevertheless one can do metallurgical examination that can proof the issue testing micro hardness. There are some old german study's that examined this issue in the very detail."
"I had a book dedicated to general grinding methods, in this book i found a test application. A normal steel block apx. 2"x2"x4" that had a large number of highly sensitive thermocouples integrated in the surface. The block was slit dry by hand over a 1000grit grinding paper. The peak temps measured, walked up to 2000°C for split seconds in the very surface (some microns). Of course the block did not melt since the volume fraction of induced heat was to tiny to affect such a large solid piece of steel. But the effect was there and proofen. In a edge we just talk about some microns of material, here the effect is solid an clear. Every manufacturer of razorblades knows this and does excessive cooling whilst grinding and polishing edges, that need to hold an super sharp edge for very long. It seems just some the magic makers out of the custom knife scene think, the physical principles like this, do not apply to them...."
Fred.Rowe
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I imagine this principle would apply when using a knife to cut especially difficult materials such as when a sawing motion is needed to accomplish the job. Its all friction. As Adam stated steel structure change is about time at temperature. What is the depth of penetration of the heat buildup. If you grind edges on a moving belt and go through a succession of grit sizes, if equal pressure and time is used along the edge, the previous damage is removed as the grit size becomes more refined. Depending on the edge desired, my last belt is a 600 grit cork with green stick on the surface. After the belt I use an ERU to remove the wire edge and strop at a matching angle. This is two or three passes. If the depth of penetration of the heat buildup is minimal, as one progresses through the different grits, I would surmise that there is little possibility of damage to the apex. This is an interesting conversation and an important one as well. If the thread generates interest in a knife maker to the point where he will take this into consideration the next time hes putting the cutting edge on a just completed knife; Mission accomplished.
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Hopefully people do not become so paranoid they stop grinding knives altogether when they realize heat migrates to the thinner edge of the blade with all post heat treat grinding.
No one is disclaiming heat is not being generated at the edge during all of these processes. What we are saying is a good knifemaker knows if the sharpening is done correctly it is rather academic and they do not suffer from paralysis through analysis.
A knife cuts well, it cuts as expect even better then expected and does all the tasks given it and it was sharpened dry. Would one then junk the knife if put under a microscope and saw microscopic evidence they do not approve of?
Knives are tools and we have gotten so good at making them some actually have to stick them under a microscope to try to find something wrong with them.
Information is good, but knowing how to apply it and when it does not apply is equally good.
If a knifemaker finds he is not good at sharpening dry, by all means do it with coolant if that is what it takes to make a knife cut the way it should.
And they should find out for each specific hardened steel what time, pressure and temperature is being generated to determine the amount and type of coolant needed to abate the 2000* Celsius temp they are worried about to solve that problem. Otherwise they would have no clue as to what they are doing to abate the high temps is actually being done.
No one is disclaiming heat is not being generated at the edge during all of these processes. What we are saying is a good knifemaker knows if the sharpening is done correctly it is rather academic and they do not suffer from paralysis through analysis.
A knife cuts well, it cuts as expect even better then expected and does all the tasks given it and it was sharpened dry. Would one then junk the knife if put under a microscope and saw microscopic evidence they do not approve of?
Knives are tools and we have gotten so good at making them some actually have to stick them under a microscope to try to find something wrong with them.
Information is good, but knowing how to apply it and when it does not apply is equally good.
If a knifemaker finds he is not good at sharpening dry, by all means do it with coolant if that is what it takes to make a knife cut the way it should.
And they should find out for each specific hardened steel what time, pressure and temperature is being generated to determine the amount and type of coolant needed to abate the 2000* Celsius temp they are worried about to solve that problem. Otherwise they would have no clue as to what they are doing to abate the high temps is actually being done.
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Roman's work considers the edge of a knife to be the last 30 microns. This is very, very small.
Fred.Rowe
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Thanks Dan, I could not find the depth being discussed.
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If sliding a steel block over 1000 grit dry (btw, what speed?) produces so much heat, then I can only imagine how much heat is generated cutting cardboard.
Should we watercool all knives when cutting stuff?
Should we watercool all knives when cutting stuff?
Nathan the Machinist
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If you can dip a blade that you have been sharpening dry into water and get it to sizzle you are probably burning it.
If you consider the first .002" of the edge as the edge (the part that once it's worn away the knife is dull and needs resharpened), an edge that is 40 deg inclusive has a sectional area of .0000015 square inches. A linear inch of that would weigh .000007 oz
This is a very small mass.
A small knife blade weighs over 2 oz. The difference is 6 orders of magnitude, similar to the difference between a paper clip and a car. You can heat a paper clip up red hot with a torch in a few seconds. A few minutes with that torch on a car will not result in a very warm car.
You can not judge a burnt edge by how hot the blade feels in your hands.
Yes, tempering is time and temperature dependent, but the time required at temperatures significantly above the tempering temperature is extremely short. If you're getting an edge that was tempered at 450 deg to 1,000 deg, even for a few seconds, it's damaged.
Now, if that blade is something like A2 that doesn't drop below HRC 55 until over 1,000 degrees, it's still going to work okay. Not great, but okay. But why go for a nice hard HRC 60 blade if you're going to reduce the actual cutting edge to something softer?
I'm not saying that everyone sharpening dry is doing this. I'm saying it's much easier to do than most people realize.
Not a great argument, IMO. I have a Chris Reeve Mnandi in my "standards" that is one of the knives I use as a control in cut tests. It often has the worst edge retention both in soft abrasive materials and in rough use, even compared to inexpensive knives. Just because someone you respect does something a certain way don't always mean they're doing it the best way. He makes very nice knives, but I'm not sure that his techniques that affect edge retention is his strongest suit.
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Nathan,
A sample of 1 is just that and not a representative sample. The point was many makers over decades and thousands of blades produced knives that have done their job as expected.
We understand the problems with heat on the edge.
But for example. How much heat is generated on the edge of your blade when you are testing them on concrete blocks or cutting through other abrasive materials by cutting and chopping abrasive materials compared to a extremely light touch on a sharpening belt for a few seconds?
Is that heat then degrading your blade to the point you put it up on the shelf because it was over heated from actual use?
Of course not.
The fact remains no one knows the temperature of the specific knife edge is getting to with the specific steel at a certain hardness with the exact pressure and time nor best coolant needed to prevent that temperature from being created. They are just guessing they are decreasing the heat but really have no clue what is going on at the microscopic level. An finer instrument possibly could detect the temperature is instantaneous and the coolant can not react fast enough to actually keep the temperature down.
Nor is there conclusive evidence of proper dry sharpening being inferior.
You could grind underwater and if improper technique were used it still not produce a good edge.
It takes more then just using a coolant to produce a good edge.
It is the skill of an experience craftsman that is required to produce the best edge with our without coolant.
A sample of 1 is just that and not a representative sample. The point was many makers over decades and thousands of blades produced knives that have done their job as expected.
We understand the problems with heat on the edge.
But for example. How much heat is generated on the edge of your blade when you are testing them on concrete blocks or cutting through other abrasive materials by cutting and chopping abrasive materials compared to a extremely light touch on a sharpening belt for a few seconds?
Is that heat then degrading your blade to the point you put it up on the shelf because it was over heated from actual use?
Of course not.
The fact remains no one knows the temperature of the specific knife edge is getting to with the specific steel at a certain hardness with the exact pressure and time nor best coolant needed to prevent that temperature from being created. They are just guessing they are decreasing the heat but really have no clue what is going on at the microscopic level. An finer instrument possibly could detect the temperature is instantaneous and the coolant can not react fast enough to actually keep the temperature down.
Nor is there conclusive evidence of proper dry sharpening being inferior.
You could grind underwater and if improper technique were used it still not produce a good edge.
It takes more then just using a coolant to produce a good edge.
It is the skill of an experience craftsman that is required to produce the best edge with our without coolant.
Adam, i believe you are the kind of guy who is likely to learn a concept and extend it to other similar cases. That's why i recommend to do a simple research about the tons of publications about the untempered white layer of martensite generated above the overtempered layer when dry working hardened steel. It does happen also rolling the steel wires without enough coolant. I don't want to point you on a specific publication, but you will easily find actually industry studies about the best acceptable compromise for cooling using a mist varying the liquid/air pressure ratio vs. resource consuming proper submerged cooling (which resulted of course the optimum).
Mine it is not sarcasm, i find interesting our discussion and consider valuable everybody's contribute to it..... i have yet to stop learning something
We could also discuss about generating heat at the edge just by cutting as intended. It happens, and is one of the many reasons why our edge needs re-sharpening, also why we often select high carbides steels for certain applications...different kind of edges.
I'm pretty happy (i don't cut cardboard mostly) i use thin keen edges pretty much always on moist foods....and i don't dry shave
Mine it is not sarcasm, i find interesting our discussion and consider valuable everybody's contribute to it..... i have yet to stop learning something
We could also discuss about generating heat at the edge just by cutting as intended. It happens, and is one of the many reasons why our edge needs re-sharpening, also why we often select high carbides steels for certain applications...different kind of edges.
I'm pretty happy (i don't cut cardboard mostly) i use thin keen edges pretty much always on moist foods....and i don't dry shave
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