Does Sharpening with a Grinder Ruin Your Edge?

Like most discussions that involve human hands, this is a matter of acquired skills, along with an understanding of what you are doing and what it is you are trying to accomplish. That is supported with a wide choice of tools and ovens.
Edges; there are as many different edge geometries as there are blade smiths. They come in many shapes and sizes. Not every one has a wet set up to grind with. I do. Makes belt work much easier. I like cork. Diamond is wonderful to sharpen on, if you know what you are doing, same goes for all techniques. Stay away from those pull thru sharpeners, the one's with the wheels on them. Gassly
 
Rick Marchand said:
I get my bevels pretty close with my 2x72 and set the final edge with a 600 CBN plate. The next step is where I'll probably get some head scratches. I do my final polish/strop on a slotted paper wheel. The slots blow air onto the blade. You can put your bare finger on it and it won't burn. Very light pressure.

I get consistently sharper and longer lasting edges, than when I strop by hand. Unless I'm using my high grit water stones and finish on a newspaper strop.... which is nice for showing off but impractical for most situations.
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Hi Rick, how do you like the CBN plate vs diamond plate? Is it longer lasting on steel?
 
john april said:
interesting article. i would be too scared to run a belt fast enough to make sparks while sharpening in the first place. i run mine really slow and just enough pressure w/120 grit to make a burr on each side, then finish with a lansky by hand. hopefully my blades edges are unscathed.
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This is the same method I've ended up with. Initially set an edge on slow belt, then work through the Lansky. It's slow, almost therapeutic, to hand sharpen. But I am only doing one at a time spread out by weeks/months.
 
Any recommendations on stones, and hand sharpening technique videos? Like knife making, there are many out there, but don't have enough knowledge base to filter out the peanut gallery.
 
stezann said:
Hi Rick, how do you like the CBN plate vs diamond plate? Is it longer lasting on steel?
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I like CBN in finer grits and DMT in rougher. The rougher CBN seems to break down quickly and the blade just skates on the surface.... or maybe I'm to aggressive
 
Thanks Larrin for another enlightening article.
Hand sharpening is a journey in and of itself. Done right, with experience, it is relaxing. Learning to do it "right", takes time, imo.
 
Thanks Larrin I really appreciate your sharing your knowledge with us. We all want to make the best knife we can and your articles really help.
I think this question has already been asked, but if sharpening on a grinder harms the temper then shouldn't we expect to see some I think the term is "oxidation color" on the edge. When steel gets hot it goes through colors. For example I have ground blades too aggressively and they have turned blue. So if the cutting edge has gotten too hot shouldn't there be some sort of color on the cutting edge that indicates the temper has been harmed?
 
I wouldn't necessarily expect color. It's highly dependent on alloy for one thing. Also it's a very small volume of material. And I don't know how the formation of the oxides changes based on a short time at high temperature rather than extended time.

Edit: Forgot to mention you are grinding away the surface as you go also.
 
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ashwinearl said:
Any recommendations on stones, and hand sharpening technique videos? Like knife making, there are many out there, but don't have enough knowledge base to filter out the peanut gallery.
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On YouTube look up Jon Broida of Japanese Knife Imports. He trained in the traditional Japanese way in Japan but the concepts he explains are the same regardless of whether you follow his exact techniques or not.

You're basically rubbing away metal from the side of the knife to form an apex at the edge. You don't know that you've removed enough until you've actually went a little too far and formed a burr that you feel. Then you abrade metal from the other side to meet at the edge in a clean apex. Usually that forms another burr. The issue is to form as small a burr as you progress and remove it because it will otherwise be a wire edge that can collapse or tear out giving a rough or damaged apex.

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ashwinearl said:
Any recommendations on stones, and hand sharpening technique videos? Like knife making, there are many out there, but don't have enough knowledge base to filter out the peanut gallery.
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Whatever your choice in stones or plates, make or purchase a set of degree wedges, which helps in reproducing accurate passes across the surface. Sharpening in this way will cut sharpening in half with better results.
 
FWIW I use all oil stones because I have to keep them in an unheated shop up here in Wisconsin. I do have some Norton water stones but like I say I can’t use them in an unheated shop in the winter.
 
Scott Hanson said:
FWIW I use all oil stones because I have to keep them in an unheated shop up here in Wisconsin. I do have some Norton water stones but like I say I can’t use them in an unheated shop in the winter.
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You sharpen by hand in an unheated shop? Man, just store em in the house, and sharpen in the house for that matter. i built a sharpening table top for my coffee table. anytime its sharpening time i just get it out, slap it on the table. my Shapton's go right on top, built in water tray and spot for the bottle mister. plop on the couch, put in a movie, and i'll sharpen for hours on end in nice climate controlled environment with full surround sound :)
 
Not so fast! The OP is a pretty sweeping generalization!!!

Personally, I do not think this article, and its contents, should be taken as complete gospel. Much of the data presented reflects what is likely the worst case scenario for a grinder. Why is this? Was it to try and prove one method is superior to the other? I don't know, but I'd love to see a similar article, where the grinders were run slower, cooler, with the proper abrasives, by an experienced professional, etc. I think the data would then prove to be much, much closer than presented here.

I hand sharpened, exclusively, for a LOT of years before I tried a grinder. Once I started with a grinder maybe 5 or 6 years ago, using good, structured abrasive belts, I haven't looked back. Though I do still hand sharpen occasionally, I generally prefer the speed, ease, and results I get using the powered method. In the course of normal use, I do not see an appreciable reduction in usable edge life from using a grinder versus a completely hand-sharpened edge, on the same knife, and at the same edge angle. I've tried that a few times, just to see. Could there be a very slight difference, if one were to be truly scientific about it? Yeah, sure there could. The disparity between the two methods may not be so high though! I value my time, and when the sharpening job at hand is a chore, I want it done quickly. Sure, there are times when it is cathartic and I enjoy it, but I am a busy guy, and more often than not, I just need the job done right, and done quickly, so I choose the grinder.

Is it possible to burn an edge with a grinder? Sure, of course it is! It can be easy to burn an edge with a grinder when working at a much higher speed than hand sharpening, especially by an amateur or with the meager 1/2" wide belts of the WorkSharp. It can happen quickly too. But this doesn't mean that every grinder will do this either, and I think a little more consideration should be given to the method in order to make this a more fair, balanced article. I personally almost never see sparks getting thrown when I'm sharpening an edge, even down to 240 grit, so sparks and extreme heat are not a given when using a grinder while dry. Too many variables at play to make such broad generalizations.

TL;DR: Now wait a minute Larrin...
 
The crux of the issue, as I see it, is that the material in question is the extreme apex of the edge. We’re talking about on a microscopic level. This may be a very small section of steel, but it’s that little part that gives extreme sharpness and maintains the geometry(sharpness) of the edge. With this section of the edge being very small, it can heat up EXTREMELY fast. As another poster said, the section can even overheat by hand sharpening(I imagine you’d need to be applying significant pressure and going somewhat quick).

So, with this microscopic section overheating, the temper is ruined there, and is compromised. Even though it’s just a small section of the edge that may be compromised, once the geometry changes, drag increases, and further degrades the edge/geometry further. Leading to a dull edge.

The steps I’ve taken to remedy the issue is to grind(grind my edges in and sharpen) on the slowest setting of my VFD/grinder and have the blade and belt wet. I just use a spray bottle on the belt and keep the blade wet contstantly. The belt is running almost comically slow and could be comparable to slow hand sharpening. I also have a Grizzly Wet grinder(Tormek clone) that pretty much operates the same. It’s nice because it takes minimal effort and I know, from my own testing, that my edges hold up.

My only complaint is the rust issue with my grinder(KMG). Does anyone use a water additive to prevent rusting? I’m thinking I might just spray paint my grinder with rustoleum and be don’t with it. Any advice on this issue would be appreciated.

To everyone else who still uses motorized sharpening/edge grinding. Do you grind wet? What kind of setup do you have. Do your findings coincide with mine?
 
Good article Larrin.

I only use a belt grinder when working on a badly chipped edge or when a edge bevel needs an aggressive re-profiling, after that I move to my Tormek T-7 or my Edge Pro for final sharpening depending on the persons preferences or intended use.

I would like to get @wootzblade commentary and insight into this article, considering their expertise and research into the subject.
 
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I used to sharpen with a grinder exclusively, now every knife that leaves my hands has a hand sharpened edge.
Very slow speed with medium worn 120 and 220 grit belts before finishing on a well worn 400 and then power power stropping on a loaded felt belt.
I did this for years and never had a single edge holding complaint from customers, actually many praises for how sharp I could get the knife.

Then I started to do a lot of heat treat experimenting, edge retention testing, and experimenting with different sharpening methods.
I started to notice that after two or three sharpenings my edge retention would actually increase.

My current process is to break the edges on the grinder and finish on DMT stones.

I had great edge holding before, but now it was even better.
I tested the edges on clean and dirty cardboard and manilla rope.

When I stopped fully sharpening on a grinder I was no longer getting increased edge retention after a couple of sharpening sessions.

Most all this testing was with 10V, 3V, and M4 with 1000 degree tempering temps.

Just because something has been done one way for a long time and is known to work does not mean it it the BEST way.

The other key is to TEST, TEST, and TEST some more.
Never be satisfied that you have a sharp edge able to cut notebook or printer paper.

Also just because someone posts a lot, be it on forums or social media pages, this does not make them an expert.
Be very wary who you take advice from and take all advice with a grain of salt.
If it makes you stop and think, test it out before claiming it as TRUTH or starting to bash someone.
 
SpyderPhreak said:
In the course of normal use, I do not see an appreciable reduction in usable edge life from using a grinder versus a completely hand-sharpened edge...
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"I couldn't tell the difference" is not very useful information. We have many decades of anecdotes pointing in every possible direction on the performance of steel, edge geometries, forging processes, heat treatment, etc. Without controlled, quantitative testing we will be stuck in the same cycle of mystery and misinformation.
 
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