mark76 wrote:


I probably shouldn't go too deeply here as it will only get confusing and off topic. When I reference 'stones' vs plates, I'm referring to the WE diamonds as plates - Just like DMT or Atomas or films are plates. They have a layer of diamonds on their surface. When I mention 'stones', that is really a misnomer for a chunk of material that has diamonds going down into the matrix not just on the surface. Typically this is a metal matrix, not a stone matrix. In all likelihood you will never see one outside of an industrial environment. They are quite expensive because they have a LOT more diamond in it and (having tested one) are largely unsuitable for hand sharpening.

I would think the WE plates ARE suitable for stone flattening, but would suggest using water for this task and being careful to cover the whole stone. More about this later ...

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Ken

So we have discussed the various types of equipment available for stone flattening up to this point. Overwhelmingly, I prefer to use diamond lapping plates for this task and will focus on this for the remainder of this discussion and let the reader extrapolate from that how to use other surfaces for flattening.

The purpose of flattening is straightforward - to produce a flat surface. This is different than producing a surface that is parallel to the back of the stone to form a perfect rectangular cuboid, but this will be covered in more detail in a post to follow.

So why do we want flatness? Well this is actually an interesting question.

I believe the answer to this is that we want a very close and uniform contact between the stone and the knife edge. Why? To give a uniform result. We don't want to just be hitting high spots but rather we want to generate a uniform surface so that as we proceed from one stone to the next we are hitting the same surface evenly. And also producing a uniform surface on the edge as well (either flat or convex but uniformly so. Otherwise if all our stones are of varying levels of 'non-flatness', we would be hitting different spots with different stones and just get a mess or patchwork - wasting metal and stone and getting an inferior result.

A flat plane also constrains the surface a bit more than a convex or concave stone surface or just a random 'wandering surface' since after all any point on the surface of the stone must be no higher or lower than the two ends of the stone even if the surface isn't perfectly parallel to the back surface of the stone. This will be discussed in detail later. The design of the WEPS also takes advantage of this property too as we will see in the next topic.

So to produce a flat surface you need a flat abrasive surface that doesn't easily ;loose it's flatness that can wear the stone down until a flat surface is produced on the stone. We will refer to an unflattened stone or stone needing flattening as being 'dished'.

Stone wear patterns are relatively unique for hand sharpeners - almost like a signature. For a device like the WE, you will still have a signature pattern - still unique to each sharpener. Just as a diamond plate will wear unevenly, a stone will too. Typically you will not - and should not - sharpen to the very ends of the stone so you should expect the least wear on the ends of the stone or diamond plate. This will result in a concave surface on your stone. You also won't wear the left and right side of the stone evenly, usually with the middle area highest but not always (individuals vary). Now if you let this go too far the sharpening angle will vary and you will get some degree of a convex rather than flat grind. This isn't necessarily terrible, BUT if the next finer stone doesn't have the same shape you get a different profile which is bad. The simplest solution is for all your stones to have the same shape, eg all equally warped. BUT the simplest shape to standardize on is a flat plane - zero warping.

Now a stone can have more wear in the center of the stone. How the hell would you do that? Well if you sharpen on the diagonal of a stone and alternate a diagonal going in the other direction you get an 'X' pattern. The overlap of the 'X' gets hit twice and wears fastest. So if you are just looking at the stone matching the flat surface, you will miss this and just see the outside flush with the lapping plate.

One of the simplest ways to correct this is to put horizontal and vertical lines on the stone with a pencil in a grid pattern - 3-4 strokes along the length and 5 or 6 across. Now as you lap the stone, you check for the remaining grid pattern. The area that remains of the grid is the DEEPEST part and you must remove stone to get EVERYTHING else ground down to that level. So you increase abrasion rates locally by pressing harder on the spots you want to grind fastest. That means pressure AROUND the deep spot, not on top of it.

So the typical wear pattern on a WE will be wear on the ends happening slowest. Some narrow knives won't even use the ends of the stone on top. Most people won't go all the way to the bottom either. This is EXPECTED and not at all unique to the WEPS but common among almost all types of sharpeners. The Pro model EdgePro tries to get around this with a ramp like device, but the cure is actually a worse solution and IMO should be disabled.

So typically you get a concave surface. So when you put the stone against the flat diamond lapping plate the two ends will touch and you get a gap in the middle. GENTLY abrade the stone surface applying pressure at the two ends of the stone. In time these two ends will come down to the level in the middle and you will get a flat surface. Just that simple. If the stone is bulging out in the middle, I tend to abrade the middle of the stone against the plate roughly perpendicular to the plate and gradually rotate the stone until it is parallel to the plate and all pencil lines are removed. In time you will need to use the pencil grid technique less and less.

It is best to do this a little at a time. It is best NOT to let a stone badly dish but just do fine adjustments or tuneups often. How often? This is a topic of endless debate. I prefer more often keeping stones more precisely flat. Similarly, I like to keep a knife sharp with minor tuneups rather than letting it get very dull and doing a major overhaul of the edge and walking around with a dull knife. If you do this with your finer grits, you can use a finer grit plate - 400 grit Atoma or DMT coarse or similar grit. If your stone is badly dished a 140 grit is preferred. For coarser stones a coarser grit is also preferred since this will give your stone more 'bite'. For your finest stones you can - after achieving flatness - texturize or surface condition the stone for improved performance. Texturizing can be another subtopic.

People new to this will say 'Why should I flatten so much - Isn't this a colossal waste of stone?' Actually no it isn't. A badly dished stone wears fastest at its lowest points and the stone will eventually fail at these low points, leaving you with a badly deformed stone, and a lifetime of poorly shaped edges coming from that stone that prematurely fails.

To give a perspective on this a 5k Shapton stone properly flattened almost every time you use the stone will last you for YEARS.

How flat is flat? This too is a topic for debate with opinions varying from don't worry about flatness to I It must be to a ten thousandth of an inch or some extreme. Remembering the phrase, 'The enemy of good is perfect' we need to strike a balance here. I'll restrict my comments to synthetic stones here for now and expand on this topic for natural stones if anyone is interested.

So you can flatten against another stone. I find I prefer more precision than this. At the other extreme, you can flatten with a very high precision diamond platen like the Shapton diamond lapping plates or some industrial steel platens. In my opinion, it makes little sense to go to extremes of ultra precise flattening plates if you cannot precisely determine when your stone has reached the point of being as flat as the plate is capable of letting you be when flattening a stone. If you get a coarser stone flat to a ten thousandth of an inch and after a few strokes it is off by a couple thousandths, you are just playing around. Ultimately the issue of relative flatness is a personal judgement call and the removal of all the pencil marks is adequate enough IMO for all my sharpening needs - and I'm a very picky sharpener. I find the use of Atoma plates and DMT plates more than adequate for flattening duty.

Stone flattening should be done using water on a diamond plate. I prefer a plate equal or (better) larger than the stone itself. If you are using a similar sized stone you need to take care that the ends are getting abraded and that as the ends of the stone pass the plate that the stone stays flat to the whole plate.

When using water you generate 'mud' as the abraded stone combines with water. This mud will eventually clog the diamond plate making it less effective. This is easily remedied with a nail brush. A quick swipe or two quickly cleans out the impacted mud from between the diamonds and lets you continue to quickly remove stone until it is flat. There are uses for this mud so you don't necessarily need to just discard it. Sometimes if you are just doing a minor amount of flattening, just leave the mud on the stone and it will give you more rapid abrasion of the steel. This sort of flattening can be accomplished in just a few seconds or a minute before using the stone for sharpening. There are other uses for mud - yet another future topic.

Now when you flatten a stone, especially when wet, the surface of the stone and the plate more and more precisely match, getting closer and closer. When it gets close enough, surface tension of the water comes into play as an ever stronger force and the plate can eventually BOND to the stone.

This is called STICTION. A flat continuous surface of diamonds can build up very strong stiction forces. If the diamonds are sufficiently coarse this is a less strong force. As the diamonds get finer stiction forces increase, so much so that the stone can stick to the plate making in near impossible to remove. Practically the DMT XXC or Atoma 140 have little stiction. A 400 Atoma also has little stiction but a DMT coarse of similar grit does have stiction issues. There are several solutions to this:

More water. This reduces the ability to squeeze out the water between the stone and the plate.

Less pressure

More speed. Keep things moving.

Don't have a continuous surface. Here the Atoma plates excel, with clusters rather than a continuous surface. This allows you to use an even finer abrasive and because there is a gap between the diamonds stiction is GREATLY reduced letting one go up to the 1200 grit plates with little stiction issues.

Flattening stones is as much a part of sharpening as anything else relating to sharpening. It is a FUNDAMENTAL skill to acquire.

I've alluded to future topics of discussion and most likely have overlooked some other subtopics, so hopefully this initial posting will generate questions and alternative opinions or points of view. I haven't discussed if you like to do circular flattening strokes or linear ones or strokes all in the same direction or cross patterns for instance (personally don't feel it is important), but welcome alternative opinions on the topic.

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Ken

Thanks again, Ken! Very useful information now more and more stones are becoming available for the WEPS.

What I wonder is why synthetic stones (and natural stones) actually have to be flattened. Or, more precisely, why they degrade/break down. And how they do it. Nearly every stone seems different. Some synthetic stones require soaking and quite a lot of water and slurry to work effectively, some stones (like the Shaptons) require only a little bit of water and the WEPS stock ceramic stones also work dry (although I wonder sometimes whether a little bit of water would not help in keeping them clean). And they all wear down differently. The WEPS stock ceramic stones don’t seem to wear at all.

My guess would be that is has something to do with the bonds in which the abrasive particles are set, but that is about as far as I can guess.

A great question, Mark! Here's the tip of the iceberg

It's not so much that synthetics wear down as much as the abrasives are released from the matrix in the spot on the stone that is used, causing the wear.

For example, the Chosera and Shapton stones for the WEPS generally wear in the middle because that is where you use them most, but not as much on the last 1-2cm of each end. The abrasive is aluminum oxide, which is still pretty hard - a 9+ on the Mohs scale. Rubbing the knife against the stone causes the abrasive to scratch, but there will always be a point where the abrasive either wears down, and/or is dislodged or pulled from the matrix.

The rate of abrasive wear is pretty much determined by the abrasive - Aluminum oxide is harder than your abrasives made from quartz, feldspar, or emery - which are about 5-7 on the Mohs. Diamonds wear the slowest, being a 10 on the Mohs scale. We'll come back to this in a minute for the second part of your answer.

Stone wear is really the rate at which the abrasives are released, and is dependent on the matrix that holds the abrasive in place. The general rule is that softer stones release abrasive faster than harder stones, and coarser stones release abrasives faster than finer stones. The theory behind this to to simply add more abrasive particles into the mix on softer and coarser stones, making them faster. (There are added perks to stones dishing readily, such as creating a convex edge, but that's another topic. We've seen how the concentration of abrasive can speed up or slow down sharpening/polishing on the pastes threads, too). So what happens here is the abrasive that is released does not necessarily break down, but the matrix holding it, does. As you get into the finer points of abrasives, you will find that natural stones' abrasive do break down while synthetics tend not to, depending on the abrasive. For this discussion, let's keep Aluminum Oxide as our synthetic abrasive since it is what the Shaptons and Choseras use, and the WEPS ceramic are probably something in the 9 Mohs range as well.

How porous a stone is also an indicator of how strongly the abrasives are held in place. More porous means more gaps between abrasives and binding agents, thus a faster abrasive releasing/wearing stone. Shaptons, for example, are not porous at all, so they hold the abrasives in place much longer, allowing for the fuller and more perfect scratch potential the aluminum oxide, which takes a while to wear down. IOW, less wear, more action, with no polish since there is little to no matrix breakdown.

Choseras, are what I consider to be slightly porous (compared to many other brands on the market), so they release abrasives at a slightly faster rate then Shaptons, but much slower than other brands. More importantly, the Choseras couple the abrasive release with the polishing effect of the binder breaking down, giving that amazing 10K polished mirror, but under the scope is slightly imperfect due to the inevitable release of the aluminum oxide abrasive particle here and there.

Getting back to the diamonds, since they wear the slowest of all abrasives, they are firmly embedded in a steel plate, with their multifaceted peaks sticking up. Because they wear so slowly, it would be an expensive waste to release them from the matrix, and is why diamonds tend to stay flatter longer - the height of the diamond is measured in microns rather than millimeters. (here's a look at some diamond plates under the scope). They will still "wear" more in the middle than at the ends but the rate is almost imperceptible when you add the overall cutting speed. Any imperfections will easily be cut through at the next diamond plate level.

SO the bottom line here is that you need to lap stones to 1. flatten them. 2. Clean them 3. texture the surface (for abrasive release rate purposes).

Thanks a real lot Tom! This is very informative!

Do I understand it correctly if I summarize it as follows? (Which was my way of learning at school .)

• Stones wear down because 1) the abrasive particles in the stones get worn down (i.e. shattered to pieces or at least scratched off) and because 2) they are released by the matrix bond.
• Effect 1) is the most important. The amount of wear depends on the hardness of the abrasive, so for example aluminium wears down faster than chromium that wears down faster than boron. (Just googled the Mohr scale <- very informative. Why do they use a different scale - the Rockwell scale - for steels?)
• Effect 2) depends on:
• the size of the abrasive particles: course stones wear faster than fine stones, probably because large particles get “hit out” easier
• the concentration of the abrasive particles: more particles means faster breakdown, probably because there is relatively less binding agent per particle
• the porousness of the stone, i.e. the gaps between abrasives and binding agents: more porous = larger gaps or more gaps = faster breakdown
• the strength of the binding agent: steel hardly releases abrasive particles (i.e. hardly wears down), whereas certain resins release the abrasive more easily.
• The breaking down of the binding agent (rather than the breaking down of abrasives) also causes a stone to polish, in addition to being abrasive. That is why the relative porous Choseras (compared to the Shaptons) polish so well at fine grit sizes.

And just trying to draw a conclusion to see whether I understand some things correctly: we can have diamond plates (a single layer - or at least not many layers) like the Wicked Edge diamond stones, comprising diamonds set in a steel plate, because the steel does not or hardly releases the diamonds and because the diamonds hardly wear. If we were to set aluminium oxide in a steel plate, the aluminium would wear down quickly and we were left with an almost clean steel plate. And if we were to set diamonds in a less strong resin, that would be pity of the diamonds that get released while still being intact.

Wow man, you guys are teaching us a real lot! We can even start to discuss which stones to use for which purposes! (I promise I won't do that - yet .).

Very curious to your comments! This weekend my first Choseras will be deflorished .

You're certainly on the right track, Mark!

I would only make one slight "correction", which is to change breakdown to abrasive or particle release rate.



We are definitely heading toward deeper discussions of "which stones for what purpose". That is where the real fun is - but before you go there, you'll need to begin forming a sharpening philosophy - Otherwise you'll go crazy chasing after each new revelation!

Thanks a lot, teacher! You should have chosen another job .

Just one thing before I start soaking my Chosera's: what is the use of water on these stones?

Obviously I have read a bit about it . Such as about the difference between slurry and swarf. A slurry is a mixture of water and stone abrasive and may help in polishing/sharpening. A swarf is a mixture of water and metal debris, which inhibits the action of the stones and is therefore undesirable.

Water helps to create a slurry and remove the swarf. (There is a nice book page on this phenomenon, too, including some controversy as to the use of slurry.)

However, why do some stones create a slurry whereas others don't? Or: why should Chosera stones be used wet and the Wicked Edge ceramic stones be used dry? (I know these latter stones can be used wet and that soapy water will probably keep them cleaner, but that is not really necessary.)

The primary use of water on stones is for lubrication and for washing off debris. However, as you begin to develop and use the paste (which is an advantageous breakdown of the abrasive mixed with water and metal bits), or mud, the water is used to keep things at a certain "concentration". For example, a popular honing method for straights using a coticule, called the "Dilucot" method, starts off with a heavy slurry concentration and gradually adds water to dilute the concentration, thus slowing down the action so that it polishes more than it cuts, ultimately ending with stone and clean water only. With no lose abrasive, it is the least invasive abrading, which is good for finishing an edge. Most synthetics work on this same premise. (Coticule's abrasive is Garnet, which are about 8-9 on the Mohs, so there is a more similar connection to Aluminum Oxide stones, rather than other natural stones).

In an odd connection to the Dilucot method, this is also why some stones like the WEPS ceramics are used dry - the texture of the surface of the stone catches the loosened abrasive and metal bits (aka dust), which are generally finer than the grit of the stone, and add more polishing/burnishing. Depending on your sharpening philosophy, you can see that as either "clogging" or "enhancing" the action of the stone. Cleaning them off will make the stone more aggressive again.

You see Arkansas stones generally promote the use of oil (which I know is your next question!), and that serves the same purpose as water, but I think oil holds the paste/swarf better. In this case, unlike the Aluminum Oxide, you have an abrasive that does like to break down, becoming finer as you use it longer. We all know how well oil attracts dirt and does not readily evaporate, so the trick is to use the same oil paste as long as you can in order to achieve a finer finish than just a clean stone - which is quite the opposite approach!

Japanese Naturals work the same as Arkansas, but they use the water just as effectively - probably (and this is a gross generalization) because the abrasives break down more readily. Ken can describe in greater detail about the stones with holes (suita?) and without, that are used purposely to catch smaller particles, much like the Ceramic WEPS.

....and we have come full circle

Thanks Tom and Mark... great input! Tom, is that why you cleaned off your slurry AND swarf before the final step with the 10k choseras in the recent video of you shaving w/ the pocket knife? I know you explained it in the video... this minimalizes the cutting action and polishes more (if I remember correctly)... am I right?

You are correct, sir!