Coarse stone sharpening

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Gradyw

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Jan 23, 2017
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After watching a few cliff stamp videos and seeing the thread on the 36 grit razor edge I had to try it. I posted ab this the other day because I never seem to be able to get a decent edge off of a coarse stone but since then I have been working on it. I think the burr was my main problem but since then I have gotten better at removing it and resharpeninf back my original angle without creating another burr. Kitchenknoves are so easy to get a razor edge on.. btw I bought a cheap ace stone with the coarse fine side just for practice and can get shaving results on the coarse side with any of the kitchen knives in my kitchen. However on some of my thicker knives it is a much harder task. Cheap throwing knives and pocket knives I have found threw out the years. My question is does a blade ever have such bad geometry or thickness that one simply won't cut? Pass the paper test or shave? Or is it just that much harder to receive the same results due to the thickness? I know geometry is a big factor in how a knife cuts but shouldn't they all be able to atleast shave and cut paper when sharpened right?
 
To my knowledge if the geometry on the edge is super thick, to get it shaving sharp you'd really need to thin it down right at the edge. I'm sure 50 degrees inclusive could shave, but it wouldn't be as easy as getting a 30 degrees inclusive angle to. At least for me most of my fixed blades won't pop hair off my arm like my Spyderco's will.

You can definitely get a thicker edge to cut paper pretty easily, but trying to shave hair requires a more acute edge than some knives come with. You could always reprofile said edge, to bring it to a smaller, sharper angle though.
 
We'll I miss mainly talking about the secondary edge and up to the spin thickness. I probably sharpen around 15-20 degrees when I'm just practicing. Old knives with god knows what kind of steel.. they do sharpen but kitchen knives are so much easier to get sharp then anything else seems like unless it's a good blade like spyderco or something I've bought since I caught the sickness everyone else has been talking about
 
Gradyw said:
After watching a few cliff stamp videos and seeing the thread on the 36 grit razor edge I had to try it. I posted ab this the other day because I never seem to be able to get a decent edge off of a coarse stone but since then I have been working on it. I think the burr was my main problem but since then I have gotten better at removing it and resharpeninf back my original angle without creating another burr. Kitchenknoves are so easy to get a razor edge on.. btw I bought a cheap ace stone with the coarse fine side just for practice and can get shaving results on the coarse side with any of the kitchen knives in my kitchen. However on some of my thicker knives it is a much harder task. Cheap throwing knives and pocket knives I have found threw out the years. My question is does a blade ever have such bad geometry or thickness that one simply won't cut? Pass the paper test or shave? Or is it just that much harder to receive the same results due to the thickness? I know geometry is a big factor in how a knife cuts but shouldn't they all be able to atleast shave and cut paper when sharpened right?
Click to expand...

I'm more and more convinced, all the time, that blade and edge geometry are the single largest detractor or contributor to sharpness in general. Thinning and/or rebevelling a poorly-cutting blade has fixed cutting performance for me, likely 99% of the time. Sometimes, it takes multiple thinning efforts over a long period of time, to finally get it to that sweet spot where it cuts well, at least. Depending on the steel, it's another issue whether it holds a good edge or not. But for me, even with 'cheap' knives, most can be made to cut/shave/slice well, or even beautifully, for at least a little while, after they've been adequately thinned at and behind the edge. And EVERY TIME, that means going down to 30° inclusive or lower, at least. All of my knives that I actually carry and use have been trimmed down to somewhere between 25-30° inclusive, with a few lower than that, before I'm even willing to put them in my pocket every day.


David
 
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The way I understand it, and my experience mirrors it, by FAR the biggest variable in how well a blade cuts is geometry. The second variable is a good solid heat treat. The third variable (a distant third) is the actual steel alloy. For example....the edge of a "tin" can lid will slice you pronto.
 
Geometry cuts, steel and heat treatment determine for how long and how thin of a geometry the blade can support. Broad steel classification is much more important than specific designation--e.g. it's a steel from the right general class for the intended context of use.
 
samuraistuart said:
The way I understand it, and my experience mirrors it, by FAR the biggest variable in how well a blade cuts is geometry. The second variable is a good solid heat treat. The third variable (a distant third) is the actual steel alloy. For example....the edge of a "tin" can lid will slice you pronto.
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I say, yes to this. DM
 
Ok well let's say we have a half inch think spine with a flat grind that's an inch and a half to the edge.(sounds horrible I know) right after sharpening on a coarse stone could it shave or slice paper or anything. 20 dps. Or is this knife just have too bad a geometry it will never be able to pass those kind of test?
 
I have been using like the worst kind of sharpening stone too. One of the five dollar six inch double side stones u can pick up from the hardware stores.. it amazes me how sharp I can get a kitchen knife with them but disappointing on a couple others
 
John Jurranich, the grand daddy of sharpening, could sharpen a double bitted axe to shaving sharpness and proved it by shaving off his thick beard with the axe when he was done. I'm not certain of the geometry of that blade (axe head), but I think it's probably as thick or thicker (primary blade face angles) than a modern tactical knife. Though I do remember Martin (HeavyHanded) saying that axes are surprisingly thin in terms of the primary blade face angles.

I've also seen big thick tactical knives shave arm hair. I don't own many thick blades, but I've sharpened a handful of them. They are certainly more difficult to make "paper cutting sharp" than thin blades. MUCH harder. Many of these blades come relatively dull from the factory, which should tell you something.

What my experience has taught me over the years is that "tactical knives" are a huge waste of time and money for me. Thin is where it's at. As the old man once told me "thin is sharp". Why do you think box cutters keep on cutting waaaaaaaay past the point that they can shave arm hair? They are thin.

I have these moments sometimes in my various hobbies and interests where I just slap my forehead and wonder how I could not see the obvious for so long. Thin blades are that kind of thing. Ever wonder why all of those old knives with 2 or 3 or 4 blades all have such thin blades? I looked down on them for many years wondering why anybody would carry such a useless knife that wasn't even a lock back! Poor, poor me. I'm such a slow student. Thin is where it's at in cutting. The makers of these traditional knives knew that lesson long before poor slow me learned it. Thin is sharp.

So can you make a big honking think blade's edge shave hair? With effort, you certainly can. But wouldn't you rather have a blade that can actually cut something well?

Check out this video from Ben Dale, the inventor of the Edge Pro, demonstrating sharpness versus cutting ability. It's pretty neat:

[video=youtube;vQKKwojVd28]https://www.youtube.com/watch?v=vQKKwojVd28[/video]

This is why I own so many Spyderco knives now. Many of them have really nice full flat grinds that really cut.

Brian.
 
I'd love to start reprofiling some of my knives but I feel like that would put too much tear on my stones. Atoma 140 and shapton glass 220. They're made for that sort of thing I think but repfoling would be like a thousand sharens seems like
 
I used a rapid metal removing file on one and it wouldn't cut for shit.. Idk ifit wore it out that bad that quick or what but I couldn't get the file to do anything
 
Shaving sharpness is fun, but doesn't reveal a lot (or anything, necessarily) about the thickness of the blade as a whole. A human hair might be up to ~100 microns thick; some are much thinner than that. In order to be 'shaving sharp', the blade only need cut to a depth equal to that hair's thickness. So the thickness of the blade, behind the edge, never comes into play at all, for shaving. For all intents and purposes, something like a sharp & thin burr on an otherwise thick edge can produce the same results, and often does. As far as angle at the very apex goes, I've noticed much better shaving performance when the edge angle stays at or below ~30° inclusive. So, even with an uber-thick blade, if the edge itself is profiled down to ~30° inclusive or lower, it can shave just as effortlessly as a scalpel with the same edge angle. Going above maybe ~35° in angle, shaving gets sort of intermittent and fleeting, relying essentially on a perfectly crisp apex or often the remnants of a sharp burr to emulate shaving sharpness, until the perfectly crisp apex isn't so crisp anymore, or until the burr folds over.

Blade thickness behind the edge makes a much bigger difference in materials cut to a greater depth, like chopping fruits/veggies, cutting cardboard, etc., as the 'thick' geometry of some blades will effectively get wedged into the material being cut, and binding against the shoulders of the bevels and upper portions of the primary grind starts to impact ease of cutting. Paper is relatively easy to cut, so long as the apex is crisp and free of burrs; but it's still pretty easy to see, feel and hear the differences in cutting ease through paper, using varying thicknesses of blades to cut it.

The obvious caveat is, if one is trying to make a big, thick blade shave hair, a lot more steel may have to be removed from the edge, over a very long effort, to arrive at exactly the same edge angle as a razor-thin blade, which only needs removing a little bit of steel, and takes only minutes to do it.


David
 
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Gradyw said:
I'd love to start reprofiling some of my knives but I feel like that would put too much tear on my stones. Atoma 140 and shapton glass 220. They're made for that sort of thing I think but repfoling would be like a thousand sharens seems like
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I currently have the first model in our upcoming Manticore series of stones slated for production, and they'll be geared quite specifically towards aggressive shaping/forming work. They'll be a whopping 60 grit in an 80/20 blend of black and green silicon carbide in a bond strength between medium-hard and hard, e.g. 3/4 of the way from medium towards hard. They should be very economical as well.
 
U may have me sold on one..forty two thanks for all the info.. that's kindve what I was thinking but being that I've only been sharpening for a couple of months or more I wasn't sure if it was my technique or what..
 
The Manticore series won't even really classify properly as sharpening stones so much as shaping stones. They're geared towards heavy stock removal work that you'd usually use a power grinder or file for.
 
bgentry said:
John Jurranich, the grand daddy of sharpening, could sharpen a double bitted axe to shaving sharpness and proved it by shaving off his thick beard with the axe when he was done. I'm not certain of the geometry of that blade (axe head), but I think it's probably as thick or thicker (primary blade face angles) than a modern tactical knife. Though I do remember Martin (HeavyHanded) saying that axes are surprisingly thin in terms of the primary blade face angles.

I've also seen big thick tactical knives shave arm hair. I don't own many thick blades, but I've sharpened a handful of them. They are certainly more difficult to make "paper cutting sharp" than thin blades. MUCH harder. Many of these blades come relatively dull from the factory, which should tell you something.

What my experience has taught me over the years is that "tactical knives" are a huge waste of time and money for me. Thin is where it's at. As the old man once told me "thin is sharp". Why do you think box cutters keep on cutting waaaaaaaay past the point that they can shave arm hair? They are thin.

I have these moments sometimes in my various hobbies and interests where I just slap my forehead and wonder how I could not see the obvious for so long. Thin blades are that kind of thing. Ever wonder why all of those old knives with 2 or 3 or 4 blades all have such thin blades? I looked down on them for many years wondering why anybody would carry such a useless knife that wasn't even a lock back! Poor, poor me. I'm such a slow student. Thin is where it's at in cutting. The makers of these traditional knives knew that lesson long before poor slow me learned it. Thin is sharp.

So can you make a big honking think blade's edge shave hair? With effort, you certainly can. But wouldn't you rather have a blade that can actually cut something well?

Check out this video from Ben Dale, the inventor of the Edge Pro, demonstrating sharpness versus cutting ability. It's pretty neat:

[video=youtube;vQKKwojVd28]https://www.youtube.com/watch?v=vQKKwojVd28[/video]

This is why I own so many Spyderco knives now. Many of them have really nice full flat grinds that really cut.

Brian.
Click to expand...

One of my favorite knives is my TOPS C.A.T. small FB. When it came from the factory it was so thick it couldn't slice an apple without exploding it the first few cuts. I believe this was done so it could be used to open oil drums, ammo cans etc. Looking at the specs for many of their offerings, most have similar dimensions. As a utility knife almost 100% useless.

I have thinned this thing out several times and I almost have trouble keeping the shoulders clean as the transition from primary to cutting bevel is only a few degrees at most. It now continues to cut cardboard etc for long stretches even as the blade dulls. And, the edge itself stays sharper longer.

Thin them out at the primary. The cutting edge ought to be 24-30° inclusive. Most budget steels will begin to lose a lot of lateral stability at <24°, especially if the primary is thin. A nice upgrade for any knifenut is a HF 1x30 and a few Norton Blaze belts 40 or 60 grit.

Thin is sharp.
 
My favorite carry knife is a cheap, but solidly built, little $4.00 Italian slipjoint that started its life as a fully serrated recurve with a really thick grind and edge. I removed the serrations and reground it to a full height hollow grind so thin that at the belly of the tip it will elastically deform under the pressure of your thumbnail and make a visible distortion on the opposite side of the blade. It's only plain old 420 stainless (not even 420HC) but it takes and holds a great edge now.
 
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