Does Sharpening with a Grinder Ruin Your Edge?

Nathan the Machinist said:
SpyderPhreak has a good point. "Does Sharpening with a Grinder Ruin Your Edge? " the answer is no, of course not. Only most of the time.

Some folks might read this thread as indicating that makers who sharpen on belts are doing it wrong (this harkens back to the old quench oil wars) when the reality is almost the only way to sharpen knives in production is using a belt powered grinder and it can be done on a powered belt grinder without overheating the edge, except the vast majority of folks sharpening on a powered grinder are, in fact, damaging their edge.

You can do it really slow. Or better, slow and wet. But most folks don't. So, yes, powered grinding can wreck an edge. Most of the time. But it is not universally a bad approach and in reality it is the only approach for folks doing it in production. So the answer to the thread "Does Sharpening with a Grinder Ruin Your Edge", the answer is no. Despite that fact that most of the time it is "yes".
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To confirm Nathan's statement that both methods can work I'd like to offer some evidence to the discussion. Years ago a good friend of mine who writes articles for various sporting magazines asked me to help him in a test. This was when those friction forged blades were just coming out, the ones that were changing the knife world forever (didn't much happen). He'd been invited to a large hog hunt put on by the maker where he took a good hog and was presented with a set of three of these knives as were all the other writers there. He wanted to try and quantify how much better these knives were then what was on the market. So the test he devised was for me to cut rope, I was the muscle and he did the tabulating. 5/8" sisal rope was cut and cut and cut. It was cut so much that we wrapped leather around the knife handles. Then we ended up using the leather wrapped handles and padded gloves. At the end of the two days we had two 55 gallon drums with 1/2" cut off pieces of sisal rope. We tested 12 knives total all from his personal collection, including one of my Rodeos (at that time from 440C at 58Rc, nowadays from AEB-L @62-63Rc), which was his personal edc. My friend, in a former life, was a well known and very well paid actor and he had a very significant and very drool worthy collection of custom knives as well as some factory knives to choose from. As a very avid hunter none of these were art knives but had been carried and used for the most part. We tested knives in FFG, hollow ground and convex ground. Each knife cut rope until it wouldn't cut rope. The backing was onto a fresh piece of fir 2x4 for each test. I then hand sharpened each knife (I was into water stones long before they were cool) and cut again until the knife would not cut. Each knife was cut with 4 times and how many cuts it made each time before it stopped cutting was recorded, with the average taken from the 3 highest for the final results. Part way through this very hand abusive couple of days I was running out of hand, I mean down right achy and the sharpening seemed to be causing more aching than the cutting. So in order to save my hands I would hand sharpen a blade 2 times and belt sharpen it the third time. It was always mixed up which of the three sharpening times was done on the belt. My method was and is done wet on a 220 silicone carbide belt and the burr wiped off on a buffer with green scratch remover basically just polishing the apex of the apex. Never more than two passes on the buffer. The results, for this discussion, were interesting in that no perceived difference presented itself. Sometime the belt sharpening out cut the hand sharpening, sometimes it didn't but in the 4 reps of cutting there was never enough difference, to make a difference, or to tell a difference if ya didn't know, which was which. In fact the results were so similar that we'd switched just to the belt sharpening by about halfway through the second day cause I was about done. Interestingly, for the point of the test, the regular knives of D2 made by the same outfit that made the friction forged blades out performed consistently, the friction forged blades which is probably why we don't hear some much about them anymore these days. He called and told them, but they didn't want to hear it and said that was impossible but the results were in. Anyhoo.

Can belt sharpening screw up an edge ABSOLUTELY, can it be done well, yep. I realize this isn't as scientific as the info presented by Larrin but I can personally testify to the blood sweat and tears involved. Not bad for a couple ol cowboys. Worst part I don't think he ever even wrote an article about it. He did buy the beer.
 
Nathan the Machinist said:
SpyderPhreak has a good point. "Does Sharpening with a Grinder Ruin Your Edge? " the answer is no, of course not. Only most of the time.

Some folks might read this thread as indicating that makers who sharpen on belts are doing it wrong (this harkens back to the old quench oil wars) when the reality is almost the only way to sharpen knives in production is using a belt powered grinder and it can be done on a powered belt grinder without overheating the edge, except the vast majority of folks sharpening on a powered grinder are, in fact, damaging their edge.

You can do it really slow. Or better, slow and wet. But most folks don't. So, yes, powered grinding can wreck an edge. Most of the time. But it is not universally a bad approach and in reality it is the only approach for folks doing it in production. So the answer to the thread "Does Sharpening with a Grinder Ruin Your Edge", the answer is no. Despite that fact that most of the time it is "yes".
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I don't know if "most of the time" is the wording to use either. After reading this thread I think "When it is done wrong" fits better.

Funny thing for me here is that I figured a lot of knife makers would know how to do it right on their grinder and would be going slow with coolant. Considering how meticulous and detail oriented knife making is it didn't dawn on me that the "majority" as Nathan says would be doing it wrong on their grinder after all the work they put into the knife.
 
Randydb said:
I don't know if "most of the time" is the wording to use either. After reading this thread I think "When it is done wrong" fits better.

Funny thing for me here is that I figured a lot of knife makers would know how to do it right on their grinder and would be going slow with coolant. Considering how meticulous and detail oriented knife making is it didn't dawn on me that the "majority" as Nathan says would be doing it wrong on their grinder after all the work they put into the knife.
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You're right, I probably misspoke. I doubt most custom makers are wrecking their edges. But I do think most production knives have this problem and many (perhaps most) custom knives are effected by it to some extent.​

I did do the controlled testing, years ago, and proved to myself that grinding the edge dry was not, from a process capability point of view, capable of sharpening a knife without edge damage. Identical test pieces with identical material, HT and blade and edge geometry. People not controlling their edge geometry and cutting random things in daily use may have too much noise in the data to see the trend. Worse, from a manufacturing point of view, you might have 100 "good" knives in a row and one bad one with a couple inches significantly softened and never notice it. If you're doing this in production, and edge performance is important to you, you need to do it wet. <--- or at least that's the conclusion I came to when I tested it. And I did real controlled testing.
 
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I think this topic comes down to experience, knowledge, and equipment. If you don’t have vfd, a cooling system, and a way to reliable set the edge geometry, do it by hand. If you use the grinder, do some testing to make sure it’s not causing problems.

This is much like the scrap steel issue. People with a lot of experience, and testing, can make a great knife from scrap steel. However, it’s mostly new makers that are attracted to scrap steel, and lack the knowledge and experience to nail the process.
 
Horsewright said:
To confirm Nathan's statement that both methods can work I'd like to offer some evidence to the discussion. Years ago a good friend of mine who writes articles for various sporting magazines asked me to help him in a test. This was when those friction forged blades were just coming out, the ones that were changing the knife world forever (didn't much happen). He'd been invited to a large hog hunt put on by the maker where he took a good hog and was presented with a set of three of these knives as were all the other writers there. He wanted to try and quantify how much better these knives were then what was on the market. So the test he devised was for me to cut rope, I was the muscle and he did the tabulating. 5/8" sisal rope was cut and cut and cut. It was cut so much that we wrapped leather around the knife handles. Then we ended up using the leather wrapped handles and padded gloves. At the end of the two days we had two 55 gallon drums with 1/2" cut off pieces of sisal rope. We tested 12 knives total all from his personal collection, including one of my Rodeos (at that time from 440C at 58Rc, nowadays from AEB-L @62-63Rc), which was his personal edc. My friend, in a former life, was a well known and very well paid actor and he had a very significant and very drool worthy collection of custom knives as well as some factory knives to choose from. As a very avid hunter none of these were art knives but had been carried and used for the most part. We tested knives in FFG, hollow ground and convex ground. Each knife cut rope until it wouldn't cut rope. The backing was onto a fresh piece of fir 2x4 for each test. I then hand sharpened each knife (I was into water stones long before they were cool) and cut again until the knife would not cut. Each knife was cut with 4 times and how many cuts it made each time before it stopped cutting was recorded, with the average taken from the 3 highest for the final results. Part way through this very hand abusive couple of days I was running out of hand, I mean down right achy and the sharpening seemed to be causing more aching than the cutting. So in order to save my hands I would hand sharpen a blade 2 times and belt sharpen it the third time. It was always mixed up which of the three sharpening times was done on the belt. My method was and is done wet on a 220 silicone carbide belt and the burr wiped off on a buffer with green scratch remover basically just polishing the apex of the apex. Never more than two passes on the buffer. The results, for this discussion, were interesting in that no perceived difference presented itself. Sometime the belt sharpening out cut the hand sharpening, sometimes it didn't but in the 4 reps of cutting there was never enough difference, to make a difference, or to tell a difference if ya didn't know, which was which. In fact the results were so similar that we'd switched just to the belt sharpening by about halfway through the second day cause I was about done. Interestingly, for the point of the test, the regular knives of D2 made by the same outfit that made the friction forged blades out performed consistently, the friction forged blades which is probably why we don't hear some much about them anymore these days. He called and told them, but they didn't want to hear it and said that was impossible but the results were in. Anyhoo.

Can belt sharpening screw up an edge ABSOLUTELY, can it be done well, yep. I realize this isn't as scientific as the info presented by Larrin but I can personally testify to the blood sweat and tears involved. Not bad for a couple ol cowboys. Worst part I don't think he ever even wrote an article about it. He did buy the beer.
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That may confirm that sharpening with wet belts doesn’t lead to overheating then, which would be nice to know for certain.
 
Just as important as these temper/sharpening issues are the ones that involve altering the temper during the final stages of putting the bevels on the blade during the manufacturing process. I wonder how many of our homemade blades have sub-optimal edge conditions because of this. I do all grinding wet, but just with a frequent misting with a spraybottle, and I slow things way down as I get closer. I don't believe that finger/temperature tests are a good metric, as I think that an over-tempered fine edge will have dissipated the excess thermal energy long before you could register it with your fingers farther back up the bevel. Consider an over-the-top fast/dry grinding with sparks for a thought experiment - you can imagine the the particle sparks themselves, if they are not totally oxidized, to certainly be past a good temper. Generally these sparks don't even hurt when they hit your bare forearms.

I just go as slow and wet as I figure is reasonable to avoid going insane, and then just hope for the best. I think my blades perform well but I've never done any well-controlled experiments. The microhardness tests are insightful but would be better if you could get closer to the edge, and I do understand the issues with doing this.

If one could set a standard geometry, a stress-strain type test, say using a micro anvil, might be a good test. Sort of hybrid uniaxial/dogbone stress/strain and microhardness test very near or basically at the edge. Anyone know of any tests of this sort?
 
Natlek said:
What about carbides , nobody mention them ? What's happening to them during sharpening edge with belts ? Vanadium carbides are harder then ceramic as I think ? So they are tear off out of the matrix ? That would be bad for edge holding , right ?
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In the name of science I will quote my self :) I don t know if everyone who participate in this thread avoid my question or perhaps you have not read it.....
Tittle of this thread is Does Sharpening with a Grinder Ruin Your Edge?
Overheating edge is one of the problem when sharpening knife on grinder .....
So this is legit question and close corellate with edge retention and affect final score on test...........What about carbides on edge ? Grain on 220 grit belt are many, many times bigger then say vanadium carbides and I can imagine what will happen when that big grain hit vanadium carbide..No way that 220 grit belt can cut and abrade/shape carbide .. . .Of course this is only my opinion :thumbsup:
In 'Maintance , Tinkerring & Embellissment part here on this forum exist many topic about that ...like this one for example
https://www.bladeforums.com/threads/high-vanadium-carbide-tear-out-questions.1626135/
 
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Is there a question you're trying to ask? I don't see the correlation between "carbide tear out" and the topic at hand, which is the possible overheating of an edge with powered sharpening. Perhaps I am missing something?
 
knowing the speed and type of abrasive used for the belt sharpening is important

There is a big difference not only due to the speed but as to the abrasive as well.

I use the Norax engineered ceramic and it is far better for sharpening due to it running perfectly flat as well as runs much cooler then the AO belts.

I currently put the initial angle on the belt grinder with a norax belt 220 grit, until it almost forms a burr at a slow speed.

Then I move to my edge pro with AO water stones and set the edge.

Setting the edge with stones and at an exact know angle .

One problem we see all the time is makers leave their edges far to thick before sharpening and result in to much time on the grinder or stones.

Run those edges thin before you go to sharpen.
 
samuraistuart said:
Is there a question you're trying to ask? I don't see the correlation between "carbide tear out" and the topic at hand, which is the possible overheating of an edge with powered sharpening. Perhaps I am missing something?
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Question is ...what is point to use CPM 15V steel if we have no carbides on edge ? IF powered sharpening tear them from edge ?
 
There is a pretty robust community of sharpening testers out there. It would probably be possible to do a blind test with a few knives.
 
Natlek said:
Question is ...what is point to use CPM 15V steel if we have no carbides on edge ? IF powered sharpening tear them from edge ?
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Does power sharpening tear them from the edge? What percentage of the edge is going to be vanadium carbides?
 
I for one simply don’t understand the question posed Natlek. The PM process gives the best carbide distribution. Along the edge and everywhere else. What is it you’re asking? Whether there are vanadium carbides at the edge, or chromium carbides at the edge, or cementite at the edge, or just plain martensite at the edge (1050 type steels), the point of the post is still valid. We are taking about overheating an apex, and that has little to do with what carbides might or might not be present on that edge.

The fact that a blade might have been tempered in the secondary hardening range might be called into question, vs an identical steel/geometry that was tempered in the lower temperatures.

But to ask about carbide tear out here....I for one don’t understand the correlation. Maybe you could expound upon your inquiry?
 
I think, Natlek asked/implied - ceramic/oa/sic belt can't effectively shape vanadium carbide, therefore most proud/decorated VC will be torn away from apex. A rough visual of this scenario:

belt vs hard carbide.png
 
When sharpening hard carbide(with diameter wider than apex radius) steels with common belt, major loss of carbides on the apex contributes to poor edge performance. This article correlated poor edge performance to ruined tempered (causation/conclusion) = incorrect, because loss of carbide causation wasn't accounted for.
 
bluntcut said:
When sharpening hard carbide(with diameter wider than apex radius) steels with common belt, major loss of carbides on the apex contributes to poor edge performance. This article correlated poor edge performance to ruined tempered (causation/conclusion) = incorrect, because loss of carbide causation wasn't accounted for.
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EDIT: Looking back through at the end of the article I didn't previously notice 4V and Vanadis 4E where mentioned, when speaking about high temperature tempering heats. They're at 3.85% and 3.7% vanadium content respectively.

Perhaps the carbide tear out issue should be mentioned at least specifically to that class of steels with 3%+ vanadium carbide content when not using CBN / diamond abrasives as another factor that could affect edge retention.

Although the carbide tear out issue isn't so much a powered or manual problem, more due to abrasive hardness and size.
 
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bluntcut said:
When sharpening hard carbide(with diameter wider than apex radius) steels with common belt, major loss of carbides on the apex contributes to poor edge performance. This article correlated poor edge performance to ruined tempered (causation/conclusion) = incorrect, because loss of carbide causation wasn't accounted for.
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Thanks for help BluntCut MetalWorks BluntCut MetalWorks , exactly what I was trying to explain ......I didn t know that my english is that bad :( I think that any type of carbide not just vanadium one will have same issue ?
 
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