Does Sharpening with a Grinder Ruin Your Edge?

Natlek said:
... I think that any type of carbide not just vanadium one will have same issue ?
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Correct. Shaping carbide and matrix at very thin cross section (the edge) is prone to poor result due to impact, which includes manual sharpening as well. Abrasive cutting points cause apex to deflect away (amt depend on sharpening angle), so end up with more burnishing/impacting than shaping, which could (most likely be 'would') weakened or dislodge carbides and produce wire-edge.

I annotated (2+ years ago) ToddS SEM image of s30v manual sharpened with SiC (iirc) stone. The apex is sub-optimal.

vSeHxg7.jpg


Even using fine diamond plate or stone, such as DMT EE or DMD 12K, where the abrasive penetrating cutting tip is est (or my wag based on experiences) about 0.3um would impact/burnish(due to edge deflection) carbide lead to weakened or tear away from edge. However this type of abrasive would work very well for large carbide and especially huge CrC (in non PM steel). Obviously need to mention: use sharp abrasive = high psi cut point = low burnish/impact.

There is additional complexity of edge trailing or leading mechanic in powered or manual sharpening. Done OTing..
 
bluntcut said:
Correct. Shaping carbide and matrix at very thin cross section (the edge) is prone to poor result due to impact, which includes manual sharpening as well. Abrasive cutting points cause apex to deflect away (amt depend on sharpening angle), so end up with more burnishing/impacting than shaping, which could (most likely be 'would') weakened or dislodge carbides and produce wire-edge.

I annotated (2+ years ago) ToddS SEM image of s30v manual sharpened with SiC (iirc) stone. The apex is sub-optimal.

vSeHxg7.jpg


Even using fine diamond plate or stone, such as DMT EE or DMD 12K, where the abrasive penetrating cutting tip is est (or my wag based on experiences) about 0.3um would impact/burnish(due to edge deflection) carbide lead to weakened or tear away from edge. However this type of abrasive would work very well for large carbide and especially huge CrC (in non PM steel). Obviously need to mention: use sharp abrasive = high psi cut point = low burnish/impact.

There is additional complexity of edge trailing or leading mechanic in powered or manual sharpening. Done OTing..
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Since it is a different subject it would probably be best to start a new thread but is there any research out there about carbide tear out? I find the idea interesting but have suspicions that there are other mechanisms at hand besides tear out. I think you probably have some of that built into your explanation as well since I saw you talked about a burnishing effect. Most of the post I have seen using machine sharpening stop at around 220 grit. Is carbide tear out a major factor at this level of coarseness ?
 
Larrin Larrin , I'm not a knife maker but I am a knife salesman and the company I am a factory sales rep for, Friedr. Dick, also makes sharpening machines for cutlery knives and machine knives & discs, your paper and this thread have been very helpful to me for my career, thank you, I've read through all the pages and every posted link and have learned a great deal, it's the best technical thread I've read so far on the BladeForums.

wootzblade said:
W B Rowe “Temperature case studies in grinding including an inclined heat source model.” School of Engineering, Liverpool John Moores University UK
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.895.1681&rep=rep1&type=pdf
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@wootzblade, your link above was a great read, way over my head but I muddled through it and gained some knowledge, thank you.

A few of my takeaways after coming to page 7:
1) Water cooled belts and wheels, but also water injection/misting at the grind point for belts.
2) I need to do more research on sanding belts and the different abrasives used on them.
3) Belt speed is also an important factor.

Machine knife sharpening is just a fact I deal with and actually sell, especially in processing. Out of the dozens of knife shops I call on that sharpen only two hand sharpen exclusively and out of the ones that machine sharpen w/a belt for the first stage very few of them are using anything to cool the belt and the ones that are their belt is going through a bath, there's no injection of water at the grind point.
 
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samuraistuart said:
So this is a thread about carbide tear out now? Ok...guess I missed the change. I thought it was about possibly overheating an edge with a grinder, which can happen with low carbide % steels or high carbide % steels.
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I think both are important considerations if you're planning on sharpening with a belt vs. a stone, though I agree, it does stray from the original topic a touch. I would certainly love to see an article with a little more about the possibilities of carbide tear out.
 
People always want all or nothing answers and want simple answers when there are actually numerous factors at play that stack.

If the steel is plus 65rc and plus 4% Vanadium with sufficient carbon to also be left as primary Carbides after HT than it will be problematic to sharpen and shape a thin radius apex on higher grit ceramic belts because it is physically not being cut properly but more rubbing and burnishing with material being moved into shape rather then cut which makes a low quality fatigued edge.
It can still be sharp but not as crisp or as much longevity that perhaps only a more discerning user can appreciate.

I don't like to talk about this subject because it leads to endless questions and arguments of folks looking for absolutes when there are many factors at play and people take a piece of the puzzle and use it out of context which doesn't help anyone.



Storm W said:
Since it is a different subject it would probably be best to start a new thread but is there any research out there about carbide tear out? I find the idea interesting but have suspicions that there are other mechanisms at hand besides tear out. I think you probably have some of that built into your explanation as well since I saw you talked about a burnishing effect. Most of the post I have seen using machine sharpening stop at around 220 grit. Is carbide tear out a major factor at this level of coarseness ?
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I remember reading knife evaluation articles in the days before BFC. One in particular reported better edge holding on a 15n20 blade when sharpened on a coarser belt vs a fine one. Now I wonder if it was just a function of coarser belts generate less heat rather than a coarse edge cuts longer.
 
Ken H> said:
First, Thank you Larrin for the article.

A question here about belt sharpening on a 2X72 which is how I normally sharpen blades. While running belt in reverse with edge up, belt speed around 300 to 400 SFPM the first grit will be perhaps 400 grit to thin edge and create a burr. This is done with finger/thumb on blade where it never even feels warm and no sparks are ever seen. Might hit with 600 to 800 grit lightly. Then a belt turned inside out with green compound to take the burr away. The knife will usually shave, slice phonebook pages, etc nicely at this point. With the edge never getting a warm feel and no sparks ever thrown - is there still danger of heat damaging the HT? Perhaps there are things happening at the microscopic level I'm not aware of?

As usual, I'm here to learn with an open mind.
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Ken, I sharpen with the edge up because I want to remove fatigued metal from the edge and i can see the angle easier since I’m looking at the top of the edge..it looks like you are starting with a bit to fine of grit. Keep in mind that I’m sharpening a lot of kitchen knives that may not of seen the best of care, along with my own custom knives...———————I start with a 120 grit Cubation II 3M belt to establish, the bevel, then 600 grit super flex Hermès to refine the edge for German/American Knives and for my own & Japanese I use a 3M Silicon Carbide 30 Micron belt, Be careful , these belts on the Mylar backing can slice into you fingers big time:eek:... Through that whole process I dip the blade in water before each pass and I only use the belts until I’ve used some 50-60 percent of the grit because they build up to much heat after that. I finish my customs & Japanese blades I sharpen with one of those yellow belts loaded with Green chrome to debut & polish....To answer your question, the belt reversed sounds like the hottest part of your technique, ??? Try dipping in water to help keep things cool!
 
Laurence, thank you for the comments. You mention:
Rhinoknives1 said:
I sharpen with the edge up because I want to remove fatigued metal from the edge
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By those words I assume you're running the grinder in forward? How fast is belt speed?

While I dip in water every pass during bevel grinding I've not done this while sharpening because of 300 SFPM belt speed, no sparks are ever thrown, and edge never feels even a bit warm to finger that rides close to edge. Based on this procedure I'd never considered any damage to the edge during sharpening, but it's hard to tell on the microscopic edge at the molecule level as some of the tests seem to indicate. That raises the question, if damage does actually occur on molecule level, how much would that show up in real work use of knife?

Thanks again for your comments.

Ken H>
 
Ken H> said:
Laurence, thank you for the comments. You mention:

By those words I assume you're running the grinder in forward? How fast is belt speed?

While I dip in water every pass during bevel grinding I've not done this while sharpening because of 300 SFPM belt speed, no sparks are ever thrown, and edge never feels even a bit warm to finger that rides close to edge. Based on this procedure I'd never considered any damage to the edge during sharpening, but it's hard to tell on the microscopic edge at the molecule level as some of the tests seem to indicate. That raises the question, if damage does actually occur on molecule level, how much would that show up in real work use of knife?

Thanks again for your comments.

Ken H>
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Ken, yes the belt is moving towards me at about 300 SFPM. It doesn’t sound like you are near hot enough to cause any damage, on a Atomic level. It’s my understanding that steel doesn’t have Molecules...I doubt you are doing any damage that would be notable.. these belt sharpening Vs Stone sharpening charts usually don’t mean a thing to me. There is the issue of time spent per knife as well as what precautions are the belt sharpeners taking to avoid overheating ??
 
Even if you keep the belts cooled with water, the high speed can still cause carbide tearouts along the edge. This is only conjecture and needs to be evaluated, but it makes sense so I'll be sticking to my waterstones.
 
Laurence, you are correct (as usual:)) there doesn't seem to be an molecules in a knife blade. Even the carbides are not actual molecules. When I said "molecule" I was just thinking of something "tiny" {g}

At 300 SFPM we're not exactly talking "high speed" - I'm with Laurance on lack of heat buildup at that low speed.
 
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cotdt said:
Even if you keep the belts cooled with water, the high speed can still cause carbide tearouts along the edge. This is only conjecture and needs to be evaluated, but it makes sense so I'll be sticking to my waterstones.
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We aren’t talking using high speed here. One thing I did a couple of times when I started analyzing belt sharpening some 20 years ago was use one of those 1 x30” 3600 rpm machines. I’m sure there is Carbide tear out and a very high chance of overheating...
 
The experience I've had is edges sharpened like that will actually cut soft material for a while. However, even the impact needed to cut a bamboo skewer will dent or damage the edge. Its deceptive damage that will show under certain circumstances but is hard to really know for sure if you're just cutting normal stuff like tape or cardboard. I have a chef's knife that will cut food quite well, but will dent on the first skewer. It would take exceptional care to see a difference if just cutting vegetables and boneless meat.
 
Storm W said:
I'm going to hazzard a guess that the cutting board is a major player in dulling kitchen knives.
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Depends on what your cutting and how. Some vegetables are inherently dirty, so they dull a lot of knives. If it's a cutting board used only for boneless meat, then the cutting board probably plays the biggest role.
 
Storm W said:
I'm going to hazzard a guess that the cutting board is a major player in dulling kitchen knives.
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The Poly Plastic boards are brutal on Culinary Knives, As Deadboxhero said, End grain natural wood is the best, but even rip cut wood boards are far more forgiving than that plastic crap.. Look at anyone’s Plastic boards and you’ll see grooves cut into the plastic, that means we’re eating the plastic:oops::eek:.. ——————-I’m 60 y/o so I don’t think the amount will harm me from eating at restaurants on occasion ..—————-———If any of you have small children , Grandchildren, Throw that plastic out and use a wooden board just like grandma used! There is a bunch of BS here in California from bought & payed for Scientists by the Plastics Council.. That plastic is cleaner & safer.. it isn’t! ————————————————————Did you ever get sick from eating at grandma’s? She had a wooden board & washed it with dish soap.. OK! Rant over! It just pisses me off! ————-Follow the money on anything and then you’ll know why!:)
 
Larrin said:
I think the title introduces this one well enough.

https://knifesteelnerds.com/2019/04/08/does-sharpening-with-a-grinder-ruin-your-edge/
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Hi Larrin. I pretty much agree with your article. But we are talking about such a small amount of steel when we talk about the apex of a blade's edge that I am not sure if the water mist isn't just cooling down the apex after it has already been heated up enough by the belt sharpening to ruin the temper.
Also, you just include hand sharpening, and not sharpening systems such as the Edge Pro types of sharpeners. When I was researching and deciding which sharpening system that I wanted to buy, I was thinking that the systems where you move the stones back and forth across the edge apex of the blade may generate enough frictional heat to ruin the edge temper themselves. Plus I wanted a system that didn't require electricity.
So after considering everything, I decided on the WE. I figured that stoning one side of the blade edge at a time may help keep the heat down on the edge apex especially if I was not sharpening too fast. Perhaps I am overthinking things but I felt like it was better to be safe than sorry.
It would be nice if someone had the equipment and resources to test the heating of the edge apex being sharpened with a thermal imaging microscope or something with the necessary resolution to handle the job.
Anyway, thanks for the article and the thread.
 
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