Curved sharpening stones

[eKretz]

I'm sorry for my irritation to spill.

You can take over this thread with your own special interest. I'm not interested in boutique knife steel circle jerk. I've read everything you said, like you're repeating it straight from this circlejerk.

Apologies.  I think I'm done. I'm way better with people before I open my mouth.

You seem to have a social issue that I don't understand. As far as I can tell I was only answering the questions that you asked. I guess I will refrain from participating in your threads from here on out. For anyone else reading, I'm not repeating anything from anyone, only relating practical personal experience. Attached are several of my own micrographs of a blade that has had carbides yanked out of the surface, both at the coarse level and fine. In more than one, you can see the carbides jutting out that are not being efficiently cut. At the coarser end the tiny black dots in the image are cavities that used to contain carbides. Judge for yourselves. Images show approximately 1mm width.

[KL27x]

Yes I do and I'm aware of it. And I apologize again. More sincerely.

So let's just be clear.
The video I made and the thread I started about convexing an arkansas stone is impractical in your opinion to the point of immediate dismissal because of
1. "modern knife steels"
2. Some blades have to be flat

1. These modern knife steels are so useful they are only in collector knives. A guy who needs a knife for a task doesn't like a knife that grows legs everytime he set is down in a working environment. He wants the tool that does the job, not a walking billboard that says "resale value for crack." Where's the S30V box cutter? M390 exacto? No? Apparently these steels are super for making feathersticks and stabbing trees. I'm hesistant to even call this a knife steel when it's only available in a general purpose tactical folder kinda deal. It it's what can be considered "modern knife steel" it should be in working knives for industrial and professional use. Where the super steel carpet knife, exacto knife, carving knife? Let alone a simple chisel? Why they only come in tactical chest piercers/box cutters? Tools which require a very keen edge are not going to benefit from these.  This is where the ark stone can be most practical usage of. To maintain keen edges. Sharpening is part of the usage of these tools.

I'm not disparaging your choice and use of your own knives. I'm sure you get a lot of value, along with the other percentage of guys buying these for other than collector item. But lets stick with the majority. 99% of people who occasional need to use sharp edges.

2. Some blades have to be flat: So far in my life and this thread I have identified 2 of these. Jointer hand plane. I wonder how many people own use one of those, today. And the other? Jointer planar knives. These are the blades in a jointer and are can be 12+" long. I suppose these must be sharpenable only on a flat stone that is wider than a foot? When I saw Matthias do exactly this, I cringed inside. To dig up and drag around a 200 lb block of stone to sharpen a 40 gram planar knife. I imagine I would just sharpen it with Tautech's granddaddy's scythe stone and a straight edge.

So I'm going to ignore these for now.

 

Before you get worked up. Consider the history of man and think what you know about this "cutting aggression" and surface area thing. Do you think man has and will always use ark stones flat, as polisher/finisher/microbevelling stones? What would they have used to sharpen their knives in the first place, then?

If they used rounded river rocks that were faster and better at sharpening than a rounded novaculite stone, then these magic river rocks would have been the valuable item.

You say you've tried this stone burnished smooth. Freshly lapped with 36 grit carbide. Try using it so it works the way it is, indefinitely, through use. This is where shines. My stones don't have a finish I refresh. The finish is in a steady state of continual use. Only if you try to use it like this can you experience the practicality of the entire system. What is advocated by the largest voices today, makes it impractical to the point of some esoteric hobby slash achievement badge.

When I say this is practical, it's because I have done it for 2 years, now.  There's pretty much no way to maintain a razor edge on knives and tools faster or more conveniently, when you consider the entire process, IMO, footprint, cleanup, maintenance. I think this might have been why these stones were valuable. Not for what we use them, today. Because this stone is unlike all other synthetic stones made today, but we try to use it the same way as all these others.

Even the sellers of these stone demonstrate this nonsense. Why would they do that? Well, smiths might get half their gross from these stones, but I bet it's 1/10th their net. That ensures people buy it, throw in in the bottom of a drawer never to be seen again, then buy some other crap. Repeat ad infinitum.

This stone might be more than it appears, if you are interested in a practical tool that is exceptional for what it is REALLY good at. You can glaze any hard wearing stone and make it play dead. Jade, granite, w/e stone you pull out of the river, probably.

A 2x4" isn't harder than aluminum oxide. But if you hold a 6" length of this flat against your belt sander, it will stop cutting once the high spots are removed, and it will start rubbing. You can stall your beltsander. Or you can continue to turn electricity into heat as long as you like. If you understand that even a tiny looking bevel on a hard steel is like a 2x4" against a belt sander, then you might start to get the picture I'm drawing. OTOH, if you take that flatened hunk of 2x4" and draw it over the round part of the belts sander, you're cutting again.

As I said once to Coppercone2 in an aluminum cube flattening project, if you wanna do it efficiently, you make it flat enough first using direct abrasion. Then you polish. You don't try to keep polishing/lapping until the cube is flat.

[eKretz]

Yes I do and I'm aware of it. And I apologize again. More sincerely.

So let's just be clear.
The video I made and the thread I started about convexing an arkansas stone is impractical in your opinion to the point of immediate dismissal because of
1. "modern knife steels"
2. Some blades have to be flat

1. These modern knife steels are so useful they are only in collector knives. A guy who needs a knife for a task doesn't like a knife that grows legs everytime he set is down in a working environment. He wants the tool that does the job, not a walking billboard that says "resale value for crack." Where's the S30V box cutter? M390 exacto? No? Apparently these steels are super for making feathersticks and stabbing trees. I'm hesistant to even call this a knife steel when it's only available in a general purpose tactical folder kinda deal. It it's what can be considered "modern knife steel" it should be in working knives for industrial and professional use. Where the super steel carpet knife, exacto knife, carving knife? Let alone a simple chisel? Why they only come in tactical chest piercers/box cutters? Tools which require a very keen edge are not going to benefit from these.  This is where the ark stone can be most practical usage of. To maintain keen edges. Sharpening is part of the usage of these tools.

I'm not disparaging your choice and use of your own knives. I'm sure you get a lot of value, along with the other percentage of guys buying these for other than collector item. But lets stick with the majority. 99% of people who occasional need to use sharp edges.

2. Some blades have to be flat: So far in my life and this thread I have identified 2 of these. Jointer hand plane. I wonder how many people own use one of those, today. And the other? Jointer planar knives. These are the blades in a jointer and are can be 12+" long. I suppose these must be sharpenable only on a flat stone that is wider than a foot? When I saw Matthias do exactly this, I cringed inside. To dig up and drag around a 200 lb block of stone to sharpen a 40 gram planar knife. I imagine I would just sharpen it with Tautech's granddaddy's scythe stone and a straight edge.

So I'm going to ignore these for now.

 

Before you get worked up. Consider the history of man and think what you know about this "cutting aggression" and surface area thing. Do you think man has and will always use ark stones flat, as polisher/finisher/microbevelling stones? What would they have used to sharpen their knives in the first place, then?

If they used rounded river rocks that were faster and better at sharpening than a rounded novaculite stone, then these magic river rocks would have been the valuable item.

You say you've tried this stone burnished smooth. Freshly lapped with 36 grit carbide. Try using it so it works the way it is, indefinitely, through use. This is where shines. My stones don't have a finish I refresh. The finish is in a steady state of continual use. Only if you learn to use it like this can you experience the practicality of the entire system. What is advocated by the largest voices today, makes it impractical to the point of some esoteric hobby slash achievement badge.

When I say this is practical, it's because I have done it for 2 years, now.  There's pretty much no way to maintain a razor edge on knives and tools faster or more conveniently, when you consider the entire process, IMO, footprint, cleanup, maintenance. I think this might have been why these stones were valuable. Not for what we use them, today. Because this stone is unlike all other synthetic stones made today, but we try to use it the same way as all these others.

Even the sellers of these stone demonstrate this nonsense. Why would they do that? Well, smiths might get half their gross from these stones, but I bet it's 1/10th their net. That ensures people buy it, throw in in the bottom of a drawer never to be seen again, then buy some other crap. Repeat ad infinitum.

This stone might be more than it appears, if you are interested in a practical tool that is exceptional for what it is REALLY good at. You can glaze any hard wearing stone and make it play dead.

Well, I appreciate the apology, so let's maybe just try to keep the tone more civil and we can continue the discussion. I am not being intentionally dismissive of convexed hones, just don't find much application for them personally except in certain cases.

Now, I've already mentioned that stones need to be used (prepped or not) differently for different purposes multiple times... You seem to want to gloss right over this. If you want to use your stone the way you're using it and it's working well for your purposes, more power to you. There's nothing wrong with that and I never said there was. That is how it should be.

Ages ago, sandstone would have been the stone of choice for coarse sharpening. Arkansas stones and their ilk (coticule, Thuringian etc.) were highly valued for their finish sharpening ability. Coarse stones like Washita and Turkish emery stones were very highly valued for quick sharpening. Until synthetics came along. Now natural stones are mostly a specialty item for people like me or you.

Next. I am not a proponent of the "super" steels and have not once said anything to that effect. My sole commentary about them has been that they're a bear to sharpen effectively with anything short of superabrasives. Again you are reading things into what I've typed that just don't exist.

Regarding your final paragraph: I can not shave my face comfortably with an edge that has been finished with a Soft Ark. If you can do that, you are doing something that pretty much no one else I know has been able to accomplish. Good for you.

Your "idea" of using the stone in its natural state is not new or revolutionary. You've been doing this for two years - I've got some I haven't resurfaced in 30. I too am a proponent of doing that... Once the stone is flat and has settled into a state where it is smooth enough for the task at hand. Surfacing the stone to a high (enough) level is exactly the same thing as long as it isn't taken to too high a level. It's just accelerating the wear so the stone gets there faster and is uniform across the entire surface... Not sure why you seem to have a problem with that.

Will I be in a great hurry to convex all my stones? No. I prefer to have a curved blade and a flat stone for razor hones. This keeps things repeatable as I progress through the grit levels from one stone to the next - this is important when the blade is guided by two point contact at spine and edge so that contact is made all the way to the apex right away in every step of the process. For the final finishing stone a convexed stone might be fine but I don't see the need, and getting a repeatable convex surface would be a total pain. It's very easy to check for flat repeatably...I am a machinist. Repeatable is sort of our thing.

For knives I really don't much care what the hone shape is, as I sharpen freehand and stone shape is mostly inconsequential if the knife blade isn't dead flat or recurved. In those cases I would find a convexed stone quite useful.

As far as flat knives or blades go - they may not be plentiful in your daily life but they are very plentiful in industries that shear paper, cloth and plenty of other materials. I'd also challenge you to find a curved sear in a pistol or rifle trigger - good luck. You aren't considering all the other things that other people might use a stone or hone to do, only your own application.

Ah, and almost forgot about the foot long blade you mentioned. Very simple, these types of blade are most efficiently sharpened on a machine tool. A surface grinder that has a table which travels in as near as possible a perfectly straight line. As fine a wheel as desired can be used, and final touch up can be done by hand if necessary.

[KL27x]

Thanks for putting up with me. Truly I appreciate everybody on the forum, esp the guys I argue with the most. 

It's way better for me to be an idiot here and to butt heads with people that know I'm slightly off, than to go try to find new people to upset. And I'm sorry when I get abusive. I have huge personality problem, and I'm aware of it. That doesn't mean I can always control it.


 

I can not shave my face comfortably with an edge that has been finished with a Soft Ark. If you can do that, you are doing something that pretty much no one else I know has been able to accomplish. Good for you.

I can't either. I can do it a couple times, but by day 3 or 4 or so, my face will call in sick. The hairs will still be jumping off, but skin is getting overexfoliated in the process. The way I look at it and do it:
1.  I grind a new apex with the soft ark, which makes a sharp and hard edge. This takes less than a minute from the time I first put the blade on the stone. This is what makes the good edge, period.
2. Polish the high spots off the bevel with the finish stone. Which I like the ruby. Just me. The sharpening stone will be plowing or furoughing the bevel. This leaves fluff on the bevel. Just like you might take your flat machine shop india and run it over a flat honed surface just to shave off burrs and high spots. That's all I want to do, here. To smooth any high spots down on the bevel. This makes the bevel feel smooth. And it improves the corrosion resistance, so water doesn't stick into these grooves. I am not trying to completely remove the scratches, at all, personally. So this polish stage is even shorter than the sharpening. The way I do it, this isn't really affecting the edge, hardly at all. But that said, ruby is a good cutter and esp when slightly rounded, of course. So this removes visible metal. I still think it will overburnish and weaken the edge if you do this too much. I'm not trying to improve the edge, here. This can make it smoother. But it can only make the edge worse, in terms of durability.

3. Strop. 3-4 swipes on the leather. The strop is what smooths my razor's edge. Way more efficient IMO then trying to polish the bevel all the way to the edge. (I don't see how the edge can stay hard that way on a hard stone like these, unless you add some lapping paste or grit. This is like holding that 2x4" against your belt sander and waiting until you take off some actual material. That doesn't make sense unless you add some lapping compound/paste.)

This is about once a month, maybe. And from watching how other people put an ark, even a soft, into their razor sharpening routine... what I just described is completely alien. If I had to do what they do, I would be back to Bic/Gillette in a heartbeat. 

I'm sorry if you feel less of my knowledge about sharpening after reading this. But it works.

My brother asks, so when start to get dull, I take the razor back to the ruby? My answer was NOO! When you don't get a good shave, start back with material removal, not polish/burnish. You might get it to cut ok with just the ruby, but it won't last very long. Waste of time.

So it's not that the soft ark is lightning faster than anything else. The reason it's efficient in my applications is because it's fast enough, and it leaves very little else left to do to the edge. The way it removes the material leaves the razor edge right there. It removes material accurately without overburnishing. Or vs a lapping stone, without that bit of roundover or whatchacallit. There's a bit of snipe when you lap, dependent on the particle size. Lapping stones won't overburnish.

You have to pay attention to how much area you have on there with the hard stones that don't slurry. If that area is too big, you will take down the high spots, then start to burnish (and to dull stone). The soft ark (when convexed) is your sanding belt that can just get all the way through this entire 2x4 (common bevel size and hardness for my tools) and keep chugging. So it will leave about the best edge while being able to actually sharpen effectively. The finer/finish hard stones like the ceramics and translucent ark are gonna stall and burnish. Just get the high spots off and quit before you get diminishing returns. Burnishing will fill in scratches with burnished metal and refine the surface, but it is changing the structure of the underlying metal, weakening it. This doesn't matter for a mirror, but it has an effect at the apex of your edge.

[KL27x]

For the final finishing stone a convexed stone might be fine ]

What people won't or refuse to understand is that this ark is sharpening fully the entire bevel, not finishing. What I'm doing is not following the bevel that was set on another stone, and occasionally hitting the apex and the back or what. This is cutting the entire bevel back. The edge (V or flat) bevel on these knives is completely formed by this stone and these movements. AND leaving the razor edge. This is the right belt to use for this, more or less. Other than for major chip out or something, this is the only stone needed to sharpen until you need a major regrind/reprofile because the edge bevel is getting too wide.

You cannot "finish" on this. Because you're removing the surface and putting a new one on as you use this. This is a sharpening stone. People who use flat ark stones might not be able to get that. Because that's not what they know about the stone.

And I can do major work the same way with the coarser india. Major like making knives from nothing.

These are the most consistent bevels on knives and the first time I consistently have symmetrical tips on my knives. The repeatability is unexplainably consistent, despite looking like all human talent or control. The motion goes on autopilot and you just ride it like a bike, you're aware of your spot, and you're holding it. Did a sharpening on one other new knife, from a coworker, a cheap winchester knife. Anyhow, used the coarse india, whip whip whip whip, and could easily stay on the factory bevel. On my knives I wouldn't care, so that was a cool test to get to have.

I'm not bragging. I'm agreeing these are legit concerns that ordinary people have. I just didn't let that stop me from trying.

If you listen to the sound in the video, you might put it together. To hear the sound that coarse and to get the shaving edge, you have to stay on the entire bevel.

Your "idea" of using the stone in its natural state is not new or revolutionary.

It seems against the norm of the ideas how to use soft arkansas stones. But this might just be the last few decades of internet. Seems like most people "recondition" to keep their stones cutting, because they are glazing them through use. I don't think this is new, either. I believe this is the way they were used for most of history. This flattening craze is perhaps spilled over from the synthetic industry and misapplied. If you believe the American internet between 2000 and 2017, there was no such thing as a convexed stone. Stones were either dished or flat. I was there and I looked. This is what our gen knows. I remember in the 90's a text webpage describing this way to use the soft arkansas. I never did it until 30 years later, though.

This is one thing you conceeded me that you admit is impressive. That I can shave right off this stone. This isn't a parlor finishing trick to massage the apex or anything. This edge is just a byproduct of the sharpening.

[coppercone2]

do you have any microscope pictures?

[eKretz]

Same for me. I can shave with the edge from a Soft Ark or even a Washita one time, but not repeatedly. I like the edge from a Spyderco Ultra Fine pretty well, which is similar to your ruby hone. Your sharpening process is pretty much the same thing I do... Coarse stone sets the edge, finer stones just smooth the remaining high spots away. Plain leather strop for the finish.

I've tried all the alternatives and every one can produce a good shaving edge but they all have their own little intricacies. I like the edges from Japanese natural stones a lot, but they are awfully expensive. As I enjoy the process and just sharpening in general I have probably spent a lot of money that to most would seem excessive and totally unnecessary. That can be said for any hobby though.

[KL27x]

Copper, for you, anything. I will try tonight. Right now I have to put some orders in with Mouser and get some adhesive added to a PCB order.

[coppercone2]

i managed to spark a 50$ knife (SOG trident) and this might fix it (battery)

[tautech]

Great discussion guys, enjoying every word !

As it progresses I'm understanding where KL27x is coming from better and better but that's not to say I agree with it 100%. It's his style of sharpening, that I fully understand but not mine......but I'm not sharpening face scrapers ! 
A single combo wet stone does 99% of what I do and another 4 or 5 stones just sit on the shelf unused.

A circular motion using the entire face of the stone has kept mine quite flat (but not perfect) over several decades.

[eKretz]

Yeah for most general knife sharpening most everything I've got is overkill. I could easily make do with a stone or three but then I wouldn't have quite as much fun!

[KL27x]

Chef's knife. Used only lightly since the last video.


My straight razor. Best I can guess, my last sharpening was around a month ago, and it has essentially been used every day since. I have done nothing to it, since. Not a single swipe on a strop other than immediately following the last sharpening.

Curiously similar to the unfinished chef knife to the eye. I finish for the feel, and my skin can't tell the difference between this and a bevel that is shiny. This ruby will make a really shiny mirror, if you want that.

This is the first time I have looked at an edge under the microscope. Not my bag. I'm impressed with myself that this looks exactly like what I described. Just knocking off the high spots. You can even see the difference, really. You can feel it.


This is a knife I ground myself, pretty close enough. It was a mora lainated blade, with a scandi grind. I chopped about an inch off the tip and obviously descandied it. eKtretz, I originally left the tip really fat, because at the time I couldn't form a good tip. I figured I would get back to it when I got better at that. After some time using these convex stones, i took this knife and finished it with the curved Norton. This is when I realized the amount of force and resistance when reprofiling on the Norton is too high to use like my razor stone; hence, i added that additional block to give it a more positive grip, and to keep the blade farther from myself when using this higher force. But otherwise, this is the best tip I ever made, anyway. And unlike trying to do it on a flat stone, where you constantly adjust your angles and squirm this way and that to get what you want? This is almost completely autopilot. The stone is the compliment of natural biomechanics, making it an ideal and infinitely adjustable tool for making various lengths and curvatures of clam-shell shapes; e.g. knife and edge shapes. Just there's no instruction manual that would make sense for it. If you wanted to learn it, you are just as well to watch someone else do it, then get on the bike and start pedaling.


Some hard evidence that perhaps I'm not prone to blowing smoke or having flights of fancy. I made two of them; this one is still unused. The other is on the saw, and has been my do-all for the last couple three years. I also increased the set of the teeth using only smooth jaw needle nose pliers. She's right as rain.

edit1: Fudge. I am gonna edit this to make the pics smaller. I forgot how to do this.
edit2: Ok, everything I do seems to just make it worse. So this is it.
edit3: I already knew this before looking under the microscope. That the bevel on the chef knife is going to be more-or-less flat but actually slightly convexed. And fairly consistently so. Everything you do on this convex stone, when using the motions I use, produces varying degrees of this slight convexity. This is not necessarily a bad thing for these tools. It is generally advantageous for sharpening. This is one of the other ways to increase the cutting and reducing the burnishing by reducing the amount of surface area on the stone while cutting in the edge. And it produces the tip very easily. You adjust your motions and the spot on the stone you are using, and this adjusts the amount of convexity you get. This is what makes it so easy to blend in the tip. I did not use a slush/lapping stone to blend things in at the end, on that tip; just a quick rub with wet/dry; you're looking at the grind right off the norton.

It's like flying a helicopter. It's hard at first, because there are so many variables you are learning, but then things settle down. Unlike a helicopter, you get to crash as many times as you want without any significant repercussions. Once you can keep in the air without thinking about it, now you can make your flight plan and stick to it. And when sharpening, you have built in GPS. You know when you're on the bevel, proper, because you can feel the tool is doing the work. I'd go so far as to say, as long as the file is chooching rather than choking, and your angle isn't higher than you like, you will end up with a razor sharp hard edge where bur falls off with mean look.

Even the edge will tend towards a slight smile/curve. You can adjust this to a lot (the gouge chisel) or a little, in order to approach flat. Flat is relative, somewhat. Just a matter of increasing the radius until it's flat enough. And a matter of controlling this motion, now that you learned to fly this helicopter. OF course on longer blades, you adjust the shape of your edge by where you spend more time. It's short blades (chisels, I guess) where perfectly straight is not going to be convenient to maintain.


eKretz, btw. When you mentioned the "high pressure" thing, I sense you watched a Stefan Wolf video. Yes, that works. But it's not overcoming the surface area and getting the stone to cut like a file. The file is still choking. This force causes the stone to crumble and release particles. Then you use this flat ark like a lapping stone. And notice how long this takes on a reported soft knife. And then there's that "microbevel" to get the schmoo off. It's a perfectly good way to use the stone, if that's your preferred paradigm. I have tried it, and... meh. Sub par. Also, the particles are of dubious efficacy, IMO. I've tried using ark dust as a stropping compound, and my conclusion is it simply doesn't cut effectively, even carbon steel. So this method just might be more of a rough/live file action as much as lapping. 

You can get the stone to chooch without curving it, too, just by tilting the blade just slightly towards the edge and drawing the blade. But this is going to quickly turn the stone into a saddle if it becomes your norm. This reverse curve hugs your bevel and increases the surface area. Then you have to fix it. Reflatten it? Or... just take the corners off and keep on chugging? Maybe your decision is different, now that you read this and will have tried it by then.



So thanks to all participants in the thread. This forum is a unique place where new ideas sometimes get to see a glimpse of daylight. When it come to these file-stones, keep your barracuda in the water. Shape first, shine little. Burr is a four letter word. Burnishing should be. Shiny != sharp. And also, don't believe for a second that all of our ancestors were nearly as stupid as we are today. And if you think knowledge can't be lost now that we have the internet? It's the exact opposite. History can be rewritten easier than ever.

In case anyone would like to know as much about machining as I pretend to, it's free and easy. Just watch ToT videos for an hour a day until you're caught up. Don't overdo it though. If you watch watch more than 2 hours in a row, you might have an existential crisis. Behind that carefree veneer and the dad jokes, Tony is a deeply troubled man. 

[eKretz]

Sorry, not familiar with Steven Wolf? Was it? I don't watch too many sharpening videos... Usually only a few of the ones someone posts in a thread and calls attention to. I don't watch a whole lot of YouTube at all really. I do like OxTools? I think it is - for machining videos though. Most of the stuff he does is done the way I'd do it.

[KL27x]

Nice. I think I'm going to like OxTools.

Not Steven. Stefan. It's kinda catchy name because it rhymes with Steppenwolf.

There's not a lot to see there. I have watched it because... I have searched every bit of knowledge about using oil stones and arkansas stones on the internet for a long time, now, trying to figure out where this curved/convexed concept went. Stefans videos are mostly just demonstrating sharpening kitchen knives on mostly synthetic stones which he likes to keep super flat by lapping on plate glass. So yeah, that's a niche thing for sure.

I remember maybe 5 or 6 years ago, when I came across a Paul Seller's blog post where he complained about the modern schools of thought on this. "In the old days, no one flattened their stones." I thought here was the master. He was there. He knows the score. Then he goes on to describe DISHED stones working fine. I have to admit the norton india (what he was describing) is such a good cutter, it probably doesn't matter how you use it, as long as you end up with the angle you want. But man, that was a disappointment. I thought I found the holy grail after 20+ years since reading that text description on the web in the 90's which described many of the benefits and reasonings behind this curve, although at the time I didn't understand all the lingo and had some internal conflicts. 

And I just don't think our ancestors didn't know how to use a file. Yet, today, check our expert knowledge. That link Gregg put in the second post of the thread. "We really have no clue what the burr is when it comes to grinding." What? It's pretty darn crystal to me.

Ah, and almost forgot about the foot long blade you mentioned. Very simple, these types of blade are most efficiently sharpened on a machine tool. A surface grinder that has a table which travels in as near as possible a perfectly straight line. As fine a wheel as desired can be used, and final touch up can be done by hand if necessary

This is fine, but it was of no use to the worker sharpening his froe, between say 500-1800's. Do you suppose he used a flat natural rock or a convexed one? (Or a dished one?) I think through a lot of this time span, they actually probably used hardened steel files for sharpening more than anything else. And we can make a new analogy. Do you suppose anyone tried making a foot wide sharpening file for this job? Perhaps. But eventually this guy figured out how files work.

Today, we know only what the advertisers/marketing dollars want us to know. Our internet knowledge is a regression to a mean in many ways. The louder voice is the truth. Our knowledge is fluid; you could say our knowledge is cultural. And today, our cultural knowledge base is highly influenced by marketing.

All of the imagined downsides of convexing this natural stone... this I will say you might be mistaken, until you have tried it. But take the crock sticks in a wood block method of sharpening. This is highly recommended and lots of folks like it. How do they sharpen their chisels and their perfectly straight jointer plane blade using crock sticks? What objections real or imagined about the what I have shown does not ACTUALLY apply to this crock stick thing? But if you suggest this crockstick, you'd get patted on the back. Good boy. If you suggest something way better and more versatile, you will be shot down in the face.

According to Jarrod, this method of using these stones was at one time a highly guarded secret. Today, you could shout it from a mountain, and it wouldn't matter. Heck, I read about it, and I still used this stone flat, only. Eventually when I dug it back out of the darkness and decided to make it work, I did it by favoring pressure by the edge to make them sharpen. After some trial, I liked the feel and the edges.  Then they dished, then I flattened them out and started over, for I dunno... a year or 2 before I just got tired of it and decided I'm going to go full vex. That's when I googled and found Jarrod's video. First time I saw anything about this since the 90's. Two years of using them like this and now I feel... there's almost no downside and huge, huge upside. I don't want to oversell it, but it's very practical.

I keep a couple of flat stones for deburring flat surfaces and as flatness-checkers, to find the high spots on a piece of steel. I would never sharpen anything on these, anyway. So I dunno what the flat arkansas as sharpening stone is even good for.  I haven't missed it. Yet. Small bits can be useful for filing and as laps used with paste. But a large flat area of novaculite is not on my top 10 ten useful tools list.

[eKretz]

Well, to put it simply the surface grinder would be of no use at all to the guys using hoes and what have you. It's totally inconsequential whether they had a perfectly straight edge or not.

Regarding the use of a flat stone, it's really no different than the use of the convexed stone when you're working on a blade with a convex curve. The blade still only makes point contact with the blade whether the stone is flat or convexed. If the blade is perfectly straight then the convex stone would offer some benefits, but also drawbacks - keeping the blade straight over time being the most significant. If that doesn't matter then there are no major drawbacks that aren't also present on the flat stone.

Convexed stones have never been any kind of secret, they've been used by tradesmen for centuries. People using scythes especially. They just may not be common knowledge to the common man - but that could be said about ALL sorts of things.

[KL27x]

Regarding the use of a flat stone, it's really no different than the use of the convexed stone when you're working on a blade with a convex curve. The blade still only makes point contact with the blade whether the stone is flat or convexed.

If you are looking just as how it cuts the steel, you are probably right.

If the blade is perfectly straight then the convex stone would offer some benefits, but also drawbacks - keeping the blade straight over time being the most significant. If that doesn't matter then there are no major drawbacks that aren't also present on the flat stone.

Yes, you recognize one major disadvantage of the flat stone in on this outwardly curved knife. There are more.

Wear pattern is the most significant other problem, IMO. When you sharpen this curved knife on the flat surface, what is going to happen to the surface of the stone, and how is it going to wear? You think you can keep the entire surface relatively flat and even? This is all the while you have to negotiate the curve of the knife, manually, while drawing it over this vast featureless area while playing keep-away-from-edge/corners? When sharpening knives, the only place you can reach the part of the edge by the handle on some knives/tools is at the edge of the stone. Are you going to compensate for that, too?

In a convexed stone, it's left to you to use and wear down the 10% extra-curved high spots (which cut better and wear faster) which develop, to keep the stone in a useful, uniform shape devoid of weird spots. In the flat stone, you are trying to wear down the 90% of the stone that is flat, in order to reach the same level as the 10% that is dished. That's a fool's errand. By the time you get close, you accidentally made a new lower low spot. You're chasing your tail the whole time and losing that battle.

Now the ones who can "actually" sharpen on this flat stone, they (nearly universally) do this by favoring pressure over just the edge of the stone, whether consciously or not, and drawing the blade over this line/area of the stone; and thus they keep the file cutting rather than gliding/burnishing. The wear pattern is just as bad, saddling the stone on the edge(s), end-to-end, because you can't practically use the whole edge all the way to the corners. I notice people on YT who use this method; at least when they are actually sharpening, not just polishing/finishing with this stone. Jef Jewell, for instance, he took the video down, but he had one where he flattened his Spyderco fine bench stone. He dished his spyderco, just like what I described, like a saddle. A superfine, sintered aluminum oxide stone. (And no, he never got that thing flat, again. At least not by the end of his video and what IIRC was over 4 hours of slave labor by his description). Imagine how much faster than happens on a piece of soft arkansas when it's actually filing, not skating/burnishing! These guys who sharpen on this soft ark like this, they frequently re-flatten these stones as part of maintenance. The stone stops working, and they might think it's because it's not flat. It's because it IS dished. And there's nothing they do (in their videos) which requires that stone to be flat in the first place, IMO.

Convexed stones have never been any kind of secret, they've been used by tradesmen for centuries. People using scythes especially. They just may not be common knowledge to the common man - but that could be said about ALL sorts of things.

The folks that used these "scythe" stones sharpened all kinds of things on them. "Scythe stone" was just a name, but we take it literally. I am guessing it is probably only in the last 100ish years we have relegated this convexed stone into this niche box for recurved edges, specifically. In fact, many a time I see people complaining about curved stones. The idea is so repulsive to them, they will argue that a narrow width stone, kept and maintained flat to be sure, will do "exactly the same thing" for these recurved blades and scythes.

Curiously, even when you buy a scythe stone, say from Baronyx Co, it comes with two flats, say the top and bottom. And the sides have some curve but only in one axis. The way you hold and use this stone, whenever you put a recurved edge on it, out-the-box, it will contact only on either/both edge(s) of that surface of the stone, until the edges of that stone wear down and the surface starts to convex.

We like flat stones. We like curved stones for recurves. We like rods for either, though? It's nothing more than cultural. We like perfection, and a flat ark stone is perfect. At being a rectangle. OTOH, if you learn and appreciate the difference between direct abrasion/filing and lapping, you might see how pointless that really is, in practice, to have a flat soft ark stone. Or maybe not.  Personally, I have as much use for a flat soft ark as I do a flat file with the same tooth geometry as my mill file but the size of a football field.

Additional shower thought #1:
I can imagine 1 good sharpening use of a flat ark. It would be good for a straight but interrupted edge. Teeth. You could, say, "sharpen" a saw blade by abrading the sides of the teeth to an edge, again, albeit with zero clearance. That kind of situation. Or for sharpening the flat side of the tips on a serrated blade. The convexed ark might round these things over just that little hair, reducing the clearance in the case of the saw. But maybe my imagination is lacking on other sharpening uses.

Shower thought #2:
The mill file the size of a landing strip would be useful for the same things as the flat ark is, just bigger. Adding straight and planar chamfers/bevels to long pieces of steel. Just breaking the edge super accurately. It would be better at keeping this "microbevel" in a straight line, in case your straightness matters to that degree. You ought to be handling this 99% in the bevel stage, though. And it would be good for making larger areas of steel shiny, by burnishing. And it would be useful for filing interrupted surfaces with adequate swarf clearance.

Even in diamond files at the fine high grits, I use a tiny file 30x for every time I use a large plate. And diamond is the only good way to cut tungsten carbide. And diamond files are way more open-pore (way larger gullets... more like a rasp) than ark stone. Thus they will cut a much larger area, relative to novaculite. There's also the bit where burnishing an apex into mashed potatoes isn't really a thing for tungsten carbide, to my knowledge.

[KL27x]

http://journals.ed.ac.uk/lithicstudies/article/view/1672/2316

Roman Quarries found in northern Germania.

In general, workshops yielded two main shapes of whetstones (with different cross-sections): parallelepiped with rectangular or square cross-sections and elliptic or circular cylinders named respectively “bar-shaped and rod-shaped”

Note "elliptic," not just rod-shapes.


A Dictionary of Greek and Roman Antiquities. Edited by William Smith and Charles Anthon.

(I'm writing it almost directly verbatim from my phone... dunno how to get the entire url to my computer, I guess I could email it, but that would be a lot of annoying tippy-tapping with my fat finger).

AC'ONE: the whetstone or Novaculite (Kirman), the same as the whet slate of Jameson, and consisting principally of silex and alum. Theophrastus informs us that the Armenian whetstones were in the most repute in his time. The Cyprian were also much sought after. Pliny confounds these with diamonds.

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This doesn't prove the Romans (or are these guys the Greeks? I think Pliny was a Greek) used elliptically cross-sectioned and/or rod-shaped novaculite for sharpening their blades. But if you tried it, you might be convinced for yourself. 

And if you have ever tried to convex the surface of a mud/lap synthetic stone, you would also be darn sure for yourself that these romans weren't making elliptical and rod-shaped pieces of softer-bonded sandstone for sharpening.

They probably also made some flat sharpening stones out of the novaculite, too. They were probably used for very small instruments. E.g., a flat piece of soft arkansas works fine for sharpening very small chisels and exactos knives, in my experience.
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Now, if you can believe modern accounts, these Armenian and Cyprian stones would have been a distant second to the Arkansas stone. And these ancients would have probably loved and been right at home with the Norton India, having had documented experience and perhaps an established preference ("confounded as diamonds") for these denser kinds of stones for their whetstones.

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This cultural preference also affects our knife profiles. Today, if our knives come from the factory with an accidental teeny bit of recurve near the guard (sometimes this is due to human input on the grinding wheel), most of us have to "fix it." And many of our knives comes with "sharpening notches" ground out of the blade next to the guard; and/or many people add them. Or we use the Japanese style kitchen knives with no guard at the base... just razor all the way. If you look at older western knives, they hardly ever had these kinds of features. Even the ones without a full bolster/guard often had an area of unsharpened blade at the base, though the name of this eludes me, ATM. And the well-used examples, sharpened many times, they developed a bit of a "boning knife" recurve next to the handle/guard. These old guys had no problem sharpening these knives. There was no special attention to this recurved area. No need to whip out a special stone or technique. It was not an issue; no extra effort or time; no string or tendons or fibers getting caught in a useless notch. My modern Case pocket knife came from the factory with a little bit of this "boning knife" grind at the guard, out the box. Case is still keeping it old school.

Perhaps one day, 100 years in the future, our descendants will find these sharpening notches to be a dead ringer that the knife dates to those years when humans became so advanced, and we became so connected and efficient in our ability to share and spread cultural knowledge, that we actually forgot how to sharpen a knife.