Ken Schwartz

[Ken Schwartz]

Dan and Mark, thank you for the kind words. Much appreciated.

So a diamond plate has a layer of diamonds typically embedded and partially exposed in a metal bond matrix, typically nickel, whereas a diamond ‘stone’ has diamonds dispersed inside the (typically harder) matrix to various depths or the entire ‘stone’. You also can have resin bonds and hybrid bonds, but this goes off topic. These ‘stones’ are typically used in industrial processes and really not suited for hand sharpening operations. These are used for tasks like polishing the insides of engine cylinders and hydraulic pressure lines are used to exert pressures well beyond hand sharpening pressures. Typically if used for hand sharpening they will glaze over because the surface won’t refresh adequately. These are also dimensionally precise ‘stones’ and not using as fine grits as we sometimes use for knife edge production. They are also rather expensive with stones barely the size of WE blanks costing hundreds of dollars.

Naguras is a large topic worth a separate discussion or several. The stones that accompany the Naniwa Chocera stones are often mistakenly referred to as nagura stones. They are not. They are simply waterstones. In this case 600 grit waterstones not too dissimilar in composition to say an 800 grit
King brand stone.. They should be referred to as cleaning stones, used to clean off metal swarf that gets caught in stones, typically from running a stone too dry. They are too small to flatten a stone adequately and can be used as a small 600 grit stone and certainly not as a true nagura stone. I rarely use these if at all. True nagura stones are a completely different topic. If a stone gets too much embedded metal swarf in it simply lapping it with a diamond plate both removes this embedded metal swarf at the same time it flattens the surface.

On to stone flattening technique in the next post. Hope this answers your question adequately.

—
Ken

This is a fascinating read, Ken! Really “everything you ever wanted to know about stones, but were afraid to ask”. And more. If you’re ever going to write a monograph, I’ll be one of the first to read it.

A quick question: what is the difference between a diamond stone and a diamond lapping plate? Two different names for the same thing, or two different things? And my local dealer sells a Naniwa Nagura stone. It this an example of what you call a modern flattening stone?

[Ken Schwartz]

Thank you Clay for putting this topic as a sticky!

—
Ken

[Ken Schwartz]

“Now lets say you do this to 10 knives. By now your stones have dished – not terribly but less than perfect (I promise to return to this more later).”

OK, I did promise. I’ll explore several methods of stone flattening here and later talk about leveling your stones. I’ll present this showing my biases and please take them as that. There’s more than one way to accomplish things. I’ll probably talk about texturizing stone surfaces later on too, a related topic, which then extends into slurry formation techniques and so on …

Ever wonder why the pyramids had stones that fit so well together? Or the Mayans or other cultures? I see some ‘experts’ marvel at this ancient precision. But yet the answer is so simple – knowledge more in the hands of craftsman than academicians. If you rub two stones together they wear the high spots off and eventually they fit closer and closer together. Indeed when using water especially they can stick SO close together that they actually DO stick together. This is termed STICTION. Stiction can be your friend OR your enemy. Now for our ancient bricklayers, even with HUGH bricks, this is good enough. For some sharpeners this too is good enough. But is it really? Well, pardoning the risque analogy, but think of two lovers and not necessarily two thin ones (sorry). Their bodies melded together as one. The bulges of one are met by the depressions of the other into a close union. But are either of them flat? Not necessarily. Or more bluntly, NO. So it is with rubbing two stones together. It is an improvement but not true flatness. For greater flatness, you use three stones, rubbing them in pairs = A+B, B+C A+C averaging out the three surfaces to a pretty precise flat surface. This is how ancient Japanese leveled their stones – and at times some still do. Ideally you would want three identical stones, but often use a coarser stone for leveling. There can be issues of grit contamination here, but that’s another topic. And these days the luxury of having three, let alone one expensive natural stone is not often practical. For a coarse natural stone to use for flattening, stones like an Ohmura or Hirashima are sometimes used, as the Ohmura can take sustained submersion.

We also have modern ‘flattening stones’ These are typically coarser stones of varying grit from as coarse as 24 grit to 120 and even 220 grit. Norton, Naniwa and more recently Nubatama have stones of appropriate coarseness that maintain their shape relatively well. They work well but eventually require flattening themselves. And here we are back to the above three stone technique. Personally I find these stones not too useful for Shaptons, because they just aren’t effective for abrading the surface of these abrasion resistant stones. But for softer badly dished stones this is an alternative.

In some instances, you can sprinkle Silicon Carbide on the surfaces of these stones to make them cut better – available in various coarse grits. You can even use Silicon Carbide on a soft metal flat surface or platen’. You can also use glass as the flat surface. I personally find this technique messy but it can be useful for coarser stones.

Some use a sidewalk for badly dished stones, plus water or not. Personally I HATE this technique because of MASSIVE contamination issues and would never recommend it. Might just be that the sidewalks I’ve used might not be good sidewalks or that people don’t care for masses of colored mud laying around – especially neighbors. Avoid this.

So we get to what I prefer for flattening stones – diamond plates. They ARE flat. How flat? This varies. Good high quality plates – Atoma and DMT are VERY flat in the range of within 0.001 inches over the surface of the plate. IMO this is more than adequate for the most discerning of tastes. You can get even flatter with the Shapton Diamond lapping plates, but I feel this is excessive. Tom might disagree 🙂 Diamond lapping plates are available in various grits. I use plates as coarse as 60 grit but typically for Atoma plates you have 140, 400, 600 and 1200 grits. For DMT (and I prefer the diasharp series) grits are 120 (XXC) 220 (XC) 320(C) and fine and extra fine (1200) and XXF(8k) You also have diamond films as an option here from as coarse as 165 microns and 125 microns up to finer and finer grits that you can use for texturizing (another topic). While the DMT plates work quite nicely and are a continuous surface of diamonds in a nickel matrix, they do develop a great deal of stiction and the more expensive Atomas offer better performance. I’ve used DMT’s for years and they are an excellent product but for stone flattening the Atomas are superb. I have not used the Wicked edge diamond plates for stone flattening yet, but because of size, they might be an alternative but something a bit larger might be better for stone flattening duty. I’d be interested to here other’s experiences here.

So you have your diamond surface. What grit is ideal? Well coarser grits leave a rougher surface texture and get the work done quicker. But they leave deeper scratches and wear the stone faster sometimes unnecessarily so. So, for a badly dished stone, use a very coarse plate (eg, 140 Atoma). For coarser stones – also a coarse plate. A finer plate on a coarse stone wears the diamond plate faster. And a very coarse plate leaves a more aggressive coarse stone surface, which is desirable. For finer stones – 1k and above, I use a 400 Atoma, since this leaves a smoother surface or a DMT coarse, however the DMT coarse has very strong Stiction issues so you need to move fast and use lots of water. This also produces a minimum of wasted stone to create flatness.

Now flattening is something to be done OFTEN. How often? Depends on usage. But even done quite often your finer stones will last for years of use. It is better to flatten as a minor touchup often than to flatten a badly dished stone. This is analogous to keeping a knife sharp with little work or waiting until it gets very dull and doing a lot of work. It is counterintuitive, but you waste LESS stone flattening than working on a dished stone. AND you get far better results and waste less metal on your knives with a flat stone. I should probably expand on this point if someone asks.

It is a matter of technique to minimize stone wear by trying to use a stone evenly concentrating on the high spots when you can. This is an issue of technique that can be discussed later.

Next, having discussed flattening equipment, we will discuss flattening technique. Please ask questions as I write these mini lessons so that I get some feedback if this is addressing issues of interest or is/isn’t hitting the mark or if I’ve explained something poorly.

—
Ken

[Ken Schwartz]

WooHoo Mark!

Looking forward to some great conversations! This should be fun!

—
Ken

[Ken Schwartz]

This is a difficult topic as no one has found a definition of sharpness that covers all cases and that satisfies all their needs for evaluation. In short, it is a tower of Babel.

Take the CATRA testing. It is essentially evaluating push cutting performance under strict guidelines. It is setup to detect the instant that a cut starts. Essentially a burst injury type of separation. It tells you very little of slice cutting performance. It also tells you little of how a blade’s overall geometry contributes or inhibits the ability of a knife to pass through an object or objects of different density. So, for instance, if you cut a cucumber slowly it may not cleanly separate, but with a bit more speed the inertia will ‘follow through’ and you get better separation. This is different than a straight push cut vs a slight slicing motion when contacting the board. People have used string extended over a platform on a scale, and taring the platform’s weight measured the point where the string is cut. This is fraught with string consistency issues, string tension issues, matching the string performance to the force range of the cut and variance along the edge, etc.

In a practical but imperfect sense, I use the ability of a knife to slice or push cut through copy paper as one index. For push cuts it is a direct downward motion perpendicular and from a point of touching the paper. I measure how far out from a pinch grip it will do this, eg push cutting 2 inches from a pinch grip. There are ways to cheat on this and edge thickness and angles change the values for equally sharpened edges. Ultimately the ideal test of sharpness is done by using the knife for it’s intended task.

Not all knives are sharpened the same along their whole length, so ultimately you have to sample along the whole length. So for instance, a deba might have a less acute angle at it’s heel than it’s tip because the heel is used for chopping off fish heads and the tip and midsection for filleting the fish so the angle is varied along it’s length in a continuously variable fashion. This CAN be done with a WE.

Sharpness is not the only goal involved in sharpening a knife. You trade for longevity of the edge, the task it will be used for and so forth. In some instances aesthetic considerations may even exceed sharpness requirements. This is a topic in itself, which can take into account both personal and cultural aesthetics. In some instances like shaving, comfort may be of equal importance to sharpness.

This doesn’t even begin a discussion of defining sharpness.

—
Ken

Quote from Ken “… I thought I knew what sharp was, but I have proven myself wrong so many times that now I just look forward to reaching the next level.”

Ken, Your statement above caught my eye.. how have you established that one blade is sharper than another? has anyone been able to get there hands on and loan us one of these ? Actually have one on order myself, it is due to be delivered just after I win the next Mega-Lotto

http://www.catra.org/pages/products/kniveslevel1/surgredst.htm B)

[Ken Schwartz]

The compounds that I sell through Clay are the 0.125 micron CBN and the 0.050 and 0.025 micron polycrystaline diamond. Note the decimal points here – 0.025 is ten times finer than quarter micron. For other coarser compounds, just contact me via PM. My wife shares your hobby of jewelry making and I act as her tech support 🙂

Extrapolating your point of view based on a 2 micron diamond sample that didn’t work out well – Well what can I say? Two microns is roughly equivalent to a 8,000 grit Japanese waterstone particle in size and this is commonly used for sharpening, so I strongly suspect that it was a ‘cheap’ quality product of unknown or low concentration, poorly formulated and at a low concentration. We need to give you a better perspective on ‘the good stuff’. Waterstones go up to half micron particles, e.g., the Shapton 30k stones and produce a spectacular edge – without benefit of a clean room 🙂 Natural stones sometimes even exceed this level of fineness and have been used for hundreds of years. I do have for instance 2 micron polycrystalline diamond and CBN products if you wanted to compare it to your earlier results too.

I’m quite confident, based on my own extensive experience and those of my customers that you are on the verge of an epiphany in your sharpening journey.

You might find this thread useful additional reading:

http://badgerandblade.com/vb/showthread.php/181913-Did-I-just-shave-with-the-world-s-sharpest-straight-%280-125-Cubic-Boron-Nitride%29

The use of these fine compounds extends to both use on precision devices such as the WE as well as freehand and belt grinder applications. Compounds as fine as 0.5 microns have been used for years in these applications for refining knife edges. Indeed I can refer to Japanese literature dating back 50 years where this is recommended for final stropping on razors. This is true for both flat and convex grinds.

Let me know if I can help you in your studies.

—
Ken

I believe I’ve mentioned this elsewhere, but for convenience, you might find these three articles I wrote useful in appreciating the difference in a well designed abrasive preparation vs some less well designed preparations – not necessarily cheaper, but more overpriced for what you are getting.

http://precisesharpening.blogspot.com/2010_12_01_archive.html

http://precisesharpening.blogspot.com/2011/01/part-2a-comparison-of-three-quarter.html

http://precisesharpening.blogspot.com/2011/01/cbn-cubic-boron-nitride-scanning.html

To repeat a quote from one of the articles:

“Quality is remembered long after the price is forgotten.”

—
Ken

Ken,

Thanks for the above information and links, and no I guess I missed them if you had posted them elsewhere. Do I undersand where to obtain your products? Is that the product that Clay is sell here? Or do you have a separate ecommerce site somewhere?

You might remember me from my previous postings: I am the “cheaper is better guy”. I came up with a mod for the WE arms that cost 5 bucks, I use red iron oxide strop compound that is used on my jewelry bench (another hobby of mine!) that costs even less ! You get the idea :cheer:

Well I am preparing another post for later today where I respond to the last 4 or five posts from others. Certain statement that some have made here have caught my eye, and I want to quote them and then respond with my humble thoughts.

One thing has happened here as a result of all this discussion that has thrown me into action: I feel that my position is not defensible if i have not put it to the test. I had a sample of a 2 micron Diamond compound from some years ago sitting on my bench. It was part of a polishing kit I obtained for working platinum jewelry. I never used it for that purpose, but did try it on a few knives. I recall that I saw very little difference in those knives after the red iron oxide polish, so hence never felt motivated to by more samples or other even finer grits. i just let the whole subject fade away. But now we are all here disussing this issue. We have all sorts of issues, points of view, various vendors of product, SEMs of blades and compounds. WHEW! it’s enough to make my old head spin!

In the face of all that information I am nagged by the thought, “What if I am wrong and they are right?” After all, I never really tried any compounds that purport to being sub micron. So not to be on here just blowing a lot of hot air, and being an inveterate fiddler I decided to go ahead and obtain some samples and give it a go. We will see where that yellow brick road ends. One thing for sure –>>> it ain’t cheap! I have been busy on the internet and have on order sets of blank handles, leather handles, various grits in a range from Clays 3.5 down to 2 to 1 to .5 (two samples that: one Chromium Oxide, One Diamond) to a no name brand .25 and now your nice looking .25 to compare it to.. so it has turned into a $$$ project, probably 300 so far and counting! Guess now a need a good 400x stereo microscope,.. Hummm, well there goes my “cheaper is better”

Will post later with some comments in response to others POV… It will take weeks to actually test my new toys, and of course I have to wait for Elk season to see if Clay is right about all this :cheer: 😉 -Dan[/quote]

[Ken Schwartz]

I believe I’ve mentioned this elsewhere, but for convenience, you might find these three articles I wrote useful in appreciating the difference in a well designed abrasive preparation vs some less well designed preparations – not necessarily cheaper, but more overpriced for what you are getting.

http://precisesharpening.blogspot.com/2010_12_01_archive.html

http://precisesharpening.blogspot.com/2011/01/part-2a-comparison-of-three-quarter.html

http://precisesharpening.blogspot.com/2011/01/cbn-cubic-boron-nitride-scanning.html

To repeat a quote from one of the articles:

“Quality is remembered long after the price is forgotten.”

—
Ken

[Ken Schwartz]

I do think it is important to understand Verhoeven’s use of razor blades for his studies. It was not chosen to be a gold standard of sharpness, but rather a matter of practical convenience.

A razor blade will fit into the chamber of a SEM (scanning electron microscope). Most knives will not. Further, the SEM chamber requires a very high vacuum. in the range of 10 to the minus 6 torr (pardon the sloppy notation). For this the gasses in the handle will ‘outgas’ and contaminate the vacuum. This is the reasoning.

Obviously these razors have extremely thin geometry and the edges are at a more acute angle than even straight razors. They typically have a much coarser finish than many of the knives we sharpen off the shelf. This is also true with most scalpels. Sharpness is more a phenomen of geometry here than finish. Go to a grocery store and using a loupe, look over any number of razor blades and you will see coarse grind marks, not refined edges.

With knives and straight razors you will see notable improvements with edge refinement. But the TYPE of edge you use is task specific. Indeed for some tasks a certain amount of ‘teeth’ is desirable, moreso for tearing type motions. Thus you can cut a tomato skin by ‘ripping’ it with teeth, eg seratted edges, or actual teeth a la the never get dull type edges. But you can also push cut a tomato in thin slices with a very refined edge, eg a tenth micron edge. Here again it is important to distinguish edge geometry from finish. You can put a shaving sharp edge on an axe for instance, but it will require a more refined edge than what would be needed on a razor.

I’m certainly not condemning experimentation regarding compounds or sharpening in general. But having tried many myself, I’ve come to prefer a more precise preparation and more precise angle control. I’ve gone to landscaping yards to try stones, used India stones, various auto polishes, green sticks, all my wife’s buffing compounds she uses for jewelry, etc etc and tossed out many tests. If I had nothing else to use, I would use them. But I prefer better alternatives.

—
Ken

[Ken Schwartz]

Well a few comments here on this post and some subsequent posts.

Regarding the medium or substrate that the compound is on:

I feel that leather does have it’s place as well as harder substrates. Of course the pressure applied makes a hugh difference here. Convexing an edge is both a measure of the substrate’s ‘give’ as well as angular consistency. So you have a range of substrates going from softest to hardest for example:

Thick neoprene / mouse pads

Thinner neoprene – various thicknesses found at dive shops – thinner has less give generally
Cardboard from corrugated to thin cardboard to card stock or index cards. This continues to various papers which can themselves be supported by various media (the substrate’s substrate).

Leather. Not all leather is the same – at all. So soft thick cowhide has much more give than thin Kangaroo hide. Here the surface characteristics also come into play. The edges I get from Kangaroo that is about the thickness of index cards allows for less convexing OR more pressure or somewhere inbetween – ie technique differences.

Woods. Various woods have different amount of give. Depending on the compound and grit sizes some are more ideal than others. I find that a slightly softer wood like Balsa is ideal for many things because the slight bit of give lets the particles stay in place a bit better. Too hard and the particles roll around. Harder woods like Baltic Birch do give a good flat surface, but particles slide around a bit too easily for my tastes. This is similar logic to using a soft steel platen to help the particles stick rather than just roll off on a harder steel surface. Of course different woods will have different abrasive properties themselves.

Paper. Revisiting this separately, paper can give one of the harder surfaces over glass, similar to films. Paper qualities become more critical at the finer grits as one competes with the clay abrasives that are a common contaminant of the paper manufacturing process, to say nothing of the abrasive qualities of the wood pulp in paper. Cotton and sugar cane pulps can give a finer finish in many instances, with cotton typically thicker stock and bagasse or cane pulp yielding very thin paper. My preference for paper with finer compounds is Rhodia or Clairfontaine. For coarser grits, just plain copy paper suffices.

Nanocloth – here you have the extreme of a neutral substrate, giving an absolute minimum of abrasiveness, allowing a pure effect from the compound applied.

Now angle control also produces convexity. So if you can control this, then the ‘give’ of the substrate is more worth consideration – like the control a WE affords.

Compounds can be put directly on film or be stuck to them as part of the manufacturing process. Like sharpening belts, there are various film substrates with specific qualities.

Waterstones – You can use various compounds on the surface of stones. This, depending on the stone gives a fairly hard surface to work with easily flattened to maintain precise flatness.

We have a similar issue with grits. Finer grits are best appreciated when other variables are controlled.

While we don’t have or need the luxury of a level five clean room, a few things will give us adequate control. KEEP strops with finer compounds in their own ziploc baggies. An uncontaminated ziploc gives you all the control of contaminants you need in a practical sense. When you aren’t using them, keep them there to reduce airborne contaminants.

There is no need whatsoever to associate what you can see in terms of finish with that being your rate limiting level of finish. You will get a mirror finish with a 5k Shapton, but certainly you can go past that in terms of sharpness. Indeed many cheap compounds do. But the biggest problem with cheap compounds is their inconsistency. You see this in particle size distribution data. You also have an issue of particle hardness with some particles eg iron oxide vs diamond or CBN. To say that a cheap supposedly 0.5 micron chromium oxide particle doesn’t require a clean room but a 0.25 particle does just doesn’t make a lot of sense.

And then there are natural stones. Here you have a hardness level that has a complex distribution and a particle size distribution equally complex with particle sizes varying during use as the mud refines, producing a more complex edge which has less of a single point of failure.

Here too you can separate the abrasive from the substrate by applying the mud produced from the stone to various substrates. Want a hakka stone that has little give? – put the mud on a hard surface (paper over glass). Want a soft version of say a Nakayama Asagi? – put it on a soft substrate like paper over neoprene. I often use balsa for these preparations. And of course you can blend natural stone slurries with CBN and diamond too for some superb effects.

Personally, I don’t think the price of a compound should be the chief concern. If a single spray of a concentrated compound of known formulation is used, the cost per sharpening is miniscule since a bottle will last SOOO long. What is more important is the value of your labor. I’m not saying this to be offensive, but having explored the realm of ultra refined small particle compounds, there truly is a difference in results best appreciated by trying it, as Clay mentions in his posting. There is sharp, there is sharper and there is even sharper. I thought I knew what sharp was, but I have proven myself wrong so many times that now I just look forward to reaching the next level.

—
Ken

Like any kind of stropping, aside from touching up the edge, it is also slowly convexing the edge. So eventually that bevel will change its shape to the convex shape we know and love. Nothing wrong with that! But if you want, it is but a few minutes work on the WEPS to get a nice sharp shoulder with the attendant bevel. Sweet!

Leo

Well you could use the strop mounted on the paddle to freehand sharpen as well, but as LEO points out, stropping on the WEPS will give you greater precision and less rounding of the edge over time. Precision stropping is especially advantageous if you are using several levels of refinement (grits) stropping as opposed to just your final strop. Of course, the compounds you use for stropping on the WEPS can be applied to bench sized strops as well. And the cheap compounds could be used on the WEPS too (not that I would recommend that, but I’m biased 🙂 )

—
Ken[/quote]

I did not realize that this thread was here on the forum, as I am a newbie to posting, and have limited understanding of how all this works. So long story short mistakenly I posted my thoughts about the above topics at:
http://www.wickededgeusa.com/index.php?option=com_kunena&func=view&catid=6&id=2304&limit=6&limitstart=6&Itemid=63 but will expand them here a bit..

Mentioned in my other post was my preference for non-leather strops and the use of cheap easy to obtain spanish cedar wood strips for a non compliant base material to hold strop compounds. I feel there is a strong case to be made for the abandonment of leather as the stropping material of choice. Now that you have a nice edge on your steel via the WEPS system, why should you convex it with a leather strop? It is the form compliant nature of leather that is causing the convexing, not the compound. I have been stropping blades for many years, experimented with all sorts of compounds and strops, and can say that (for me anyway..) the evil-doer of a bad strop is ( in order of issue..) : 1.) a compliant base material 2.) bad hand technique 3.) and running a distant third (if at all) is the compound itself.

For what is worth, I feel that in the world of knife sharpening, once you get past the level of any compound that is capable of mirroring the metal to the naked eye then you at the limit of what you can reasonably achieve for the purpose of knife sharpening. Discussions of 0.25 micron high purity CBN sprays and the like, are to me (sorry not trying to offend anyone) are more or less of an exercise in nonsense and probably frustration. It takes very specialized, and very expensive equipment to apply such abrasives in a productive way. If you are a technician in a Class 5 clean room, with the right equipment, and the task at hand is flattening the base for a space satellite sensor then yes maybe we should be talking sub micron abrasives.

So I say, go ahead and use “cheap compounds” … experiment, and have fun![/quote]

[Ken Schwartz]

Thanks for that Ken.
I did some searching and could not find an email address for you. How would one get in touch with you?
I have checked out your blog in the past and seen your pagges at Chefsknivestogo. But no email found.

Thanks,
Phil

ksskss at earthlink dot net – I’ll send you other contact info from there (skype, phone, etc)

—
Ken

[Ken Schwartz]

I do offer diamond lapping film going from 165 microns up to 0.1 microns. I can bring these over to the WE platform for those interested. I have found that I get more precision from these films if they are mounted on glass over the blanks and can do this for the WE.

Anyone interested? I have about 15 grits inbetween the 165 and 0.1 micron range. In a few instances, I also have several formulations that are either more robust or delicate depending on your requirements.

I also offer these in 1×6, 2×6 and 3×8″ sizes.

—
Ken

[Ken Schwartz]

Clay, the samples are on the way 🙂

—
Ken

Ken,

Thank you so much for your input! I too really appreciate an owner of his business who gets involved in the furthering of his products… rock on Clay! And I also want to thank everyone else who has contributed (especially Tom)… all the info posted has been very helpful.

So Ken, where would one get this “kangaroo leather” for the WEPS paddles? And what about the nanocloth? I am very interested in looking into that… please post a website if Clay is good w/ it =) Thanks

For now, you can contact me directly – (ksskss at earthlink dot net). In time, if Clay likes it, you can get it from him directly.

—
Ken[/quote]

You’d have to send me some samples :cheer:[/quote]

[Ken Schwartz]

Just thinking out loud here, buy you could round off or shape the END of a stone with a coarse diamond plate to the desired radius of a concave grind, lock the stone handle in place and do sweeps only along the blade’s edge. I wouldn’t recommend the effort however as ultimately the ANGLE at the edge of the edge is the critical parameter and you would get an unnecessarily delicate edge. You are ultimately limited in how acute the final edge is on your blade by the steel’s capacity to take an acute edge. For concave grinds the opposite side of the concavity limits the sharpening angle unless the abrasive surface is round / convex, like a grinding wheel. And here, you would ideally want a wheel of the same diameter as the radii of the concave surface.

If you look at a traditional Japanese Straight razor (kamasori), it has two concave sides, yet the final bevels are ground flat on both sides. Same with Western style straight razors. It is a pretty firmly established concept. This is also true with concave ground pocket knives, eg a Jess Horn Spyderco ZDP-189 blade or a Gayle Bradley Spyderco CPM-M4 blade.

For a Japanese traditional single bevel kitchen knife the back of the blade is also hollow ground. But this hollow back or urasaki is ALSO ground flat along the rim of the concavity. There is a pattern here in how one handles a concave shaped blade with a flat grind for the final edge. Same with Japanese chisels too.

—
Ken

[Ken Schwartz]

Well Kangaroo strops are worth a whole separate post. I’ll include some high power pics of the surface in that post. I’ll be sending out a sample for Clay to try, along with some nanocloth.

Basically the surface is SUPER smooth, yet has good draw. As soon as you touch it, you will immediately ‘get’ what it is all about. It is also VERY thin, yet sturdy, so you get much less convexing of your edge – more precision on your flat grinds and more control convexing your convex edges. If you wish, you can press harder on ‘roo than other thicker leather to get a similar degree of convexity if you want to be more aggressive, although I prefer to take advantage of it’s precision with a more gentle ‘hand’.

It works extremely well just by itself as a final finisher and also more fully takes advantage of ultra fine stropping compounds like the 0.1, 0.025 and 0.050 micron compounds. You can use it to significant advantage as a final strop coming from a polishing stone like the 10k Chocera or 15k or 30k Shapton Pro to further enhance the edge too.

—
Ken

[Ken Schwartz]

Clay / Leo

Thanks for the kind comments and warm reception. Clay, you stated a definition of asymmetry very accurately. You can have asymmetry determined by simply measuring the widths of the bevel on each side of the knife. If the bevel widths re equal this is 50/50. If it is 70/30, the ratio is 7 units long on one side to 3 units long on the other. This holds true if the two angles are 30 degrees or 15 or anything else.

You can also have angle asymmetry, even with equal length bevels.

And you can have BOTH subtypes of asymmetry at the same time.

As a precision device, the WE is rather unique in this regard in that you can accomplish this combined asymmetry of both angles and bevel widths with ease in a consistent and repeatable fashion.

You see blade asymmetry often on Japanese Kitchen knives. The knife ITSELF is asymmetric, biased to the right. This puts the edge a bit off of dead center relative to the spine. So if the edge gets centered, it is a bit offset from the knife’s overall geometry. This causes the knife to steer or veer off to one side and you have difficulty cutting straight cuts. This is less noticable on thin items like green onions and very noticable on larger items like melons, where you get cuts in arcs rather than straight lines, or when cutting thin slices of cheese that you have trouble getting constant widths. The solution? Match the edge asymmetry with the blade’s asymmetry so the force of the knife coming down is aligned with the knife.

In practice, unless you are VERY fanatic, you don’t necessarily measure bevel widths with a calibrated graticule (OK, yea I’ve done that), but just ‘eyeball’ the relative bevel widths. This is much like getting a wheel alignment.

Here again the WE is particularly well suited because of it’s repeatability. You set the WE up with the angles you want on each side, sharpen the knife and try it out. If it steers, you go back and grind some more on one side until you have trued the knife to perfection. Same angles. A perfect way to fine tune a knife precisely to your needs. Then refine the edge.

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Ken

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