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?

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.

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Ken



mark76 wrote:

Excellent stuff, Ken!

Keep it coming!

Thanks again, Ken. I think I understand your explanation of the difference between stones and plates. The only thing I don't understand is that these stones are so expensive. The Wicked Edge diamond stones cost $65 for two paddles. That is not exactly cheap, but also not hundreds of dollars per stone. Or are the WE diamond stones technically diamond plates?

And to make a shortcut: is a course or medium WE diamond stone suitable for flattening a fine WE Chosera stone?

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