Lapping Plates and stones

[Dale Coons]

I bought a DMT DIA-Flat lapping plate a while back (it's a fairly new product--4 x 10 inches with 120 micron diamonds bonded to a 3/8" thick surface) and it does a great job on the norton stones I've had for a while--way better than the norton "flattening" stone. A couple of the ones I have are starting to wear and I'm thinking about moving to something that is less mess--perhaps some of the ceramic stones.

Anybody had any experience using that plate with something like glass stones? Chris Shwartz mentioned he'd sharpened his shaptons about 200 times on one, but doesn't say what kind of stones exactly they are.

I'd hate to bugger up a really nice sharpening stone using something to flatten it I shouldn't. This one isn't cheap, but a lot less than some other lapping plates that have breath-taking prices. Any experience/direction out there?

[Jim Matthews]

This should work fine. The Shapton system uses a loose grit on a milled steel plate.
You might be able to "refresh" the DMT if it stops cutting with a similar application.

In any case, the abrading surface will wear down over time. I doubt I'll sharpen my Shaptons 200 times in my life...

[Jason Coen]

That's exactly what I use to flatten the Glasstones I still have in rotation (and oilstones, and the backs of several old paring chisels, and anything else that needs it). I've completely worn out the 1k GS in about 18 months. Not the fault of the plate, as it works exactly as I hoped it would, but rather an indictment of the 1k GS.

[Jason Coen]

You might be able to "refresh" the DMT if it stops cutting with a similar application.



I'll be shocked if anyone other than a professional sharpener wears out one of the new Dia-Flat lapping plates. They hold up unbelievably well.

[Stuart Tierney]

The Dia-flat will work fine on Glass Stones.

FWIW, the Dia-flat is the 3rd most expensive waterstone flattening device commercially available, behind the 2 Shapton diamond flatteners and slightly ahead/equal with the Shapton plate/powder system.

Honestly, I'd prefer the Shapton things if I was going to spend more than $100 on a flattening device. I'd have to be strongly coerced to choose the Dia-flat over any of them.


Stu.


(Who's yet to be convinced in any way, shape or form that the Dia-flat is an actual solution to a real, tangible problem rather than an overkill solution that missed the mark (point) completely. Sorry.)

[John Coloccia]

The Dia-flat will work fine on Glass Stones.

FWIW, the Dia-flat is the 3rd most expensive waterstone flattening device commercially available, behind the 2 Shapton diamond flatteners and slightly ahead/equal with the Shapton plate/powder system.

Honestly, I'd prefer the Shapton things if I was going to spend more than $100 on a flattening device. I'd have to be strongly coerced to choose the Dia-flat over any of them.


Stu.


(Who's yet to be convinced in any way, shape or form that the Dia-flat is an actual solution to a real, tangible problem rather than an overkill solution that missed the mark (point) completely. Sorry.)

What do you recommend, Stu? I use a Duo (coarse for flattening). For me, sharpening isn't an experience. It's a chore that gets in the way of my real work, and I have an arsenal of sharpening equipment that I use for different situations...whatever gets me there the fastest and with least amount of work. For someone like me, what would you recommend?

[Jason Coen]

(Who's yet to be convinced in any way, shape or form that the Dia-flat is an actual solution to a real, tangible problem rather than an overkill solution that missed the mark (point) completely. Sorry.)

To each his own. What else is out there of an equivalent size that won't wear out quickly (like the DGLP - ask me how I know), doesn't use loose granules, or requires replacement sheets every time you wear out the surface?

The Dia-Flat has been as simple and as reliable as a hammer so far. I don't want to have to think about all the ancillary stuff that goes along with those that apparently hit the mark. Take it out, use it, put it away - what else is there to get right?

[Dale Coons]

Thanks all. Stu, since I already own the dia-sharp I wasn't looking to get another solution unless I had to. Sounds like it will work fine with whatever I wind up getting. You seem to be rather an expert in this area, so along with seeing what you recommend to John, I'd like your opinion on a good set for me--I'm not a neander by any stretch, but I do like sharp chisels and planes. I really hate the mess and soaking with the full set of nortons I have (220 thru 8000--the 220 is for rehabbing my granddad's chisels that my uncle used for a screwdriver, lever, etc), but do like the way the waterstones sharpen. I'm willing to pay for quality, but I'm not looking to break the bank.

[Stuart Tierney]

What do you recommend, Stu? I use a Duo (coarse for flattening). For me, sharpening isn't an experience. It's a chore that gets in the way of my real work, and I have an arsenal of sharpening equipment that I use for different situations...whatever gets me there the fastest and with least amount of work. For someone like me, what would you recommend?

Is the Duo flat? Yes? Then use it up!

I've got a Duo, and it works quite nicely some of the time. It is not my first choice for flattening stones because of the stiction and it doesn't seem to really 'bite into' the stones like the other options I do have. I do have some stones that I believe the Duo (XC) will be completely ineffective with due to it's design and the stone being flattened, not the diamond size or application to the plate. Of course, I've not even bothered trying it because previous experience tells me that the Duo will be ineffective and I don't want to use up that plate for nothing.

And the experience off the Duo is what troubles me about the Dia-flat. I have NO doubt it's a useful device that works well most of the time, and as is wont to happen, those who own XYZ device and have good results will defend their choice. This is good, since again, I have NO DOUBT WHATSOEVER that the Dia-flat works as well as advertised.

What I'm not convinced about is the size of the thing. I've performed thousands of stone flattenings (I can supply written documentation for over 1000 of those flattenings), and all done with an Atoma #400 that is no longer or wider than the stone it's flattening. I've made video showing that the stone is indeed flat after flattening, and that the Atoma did the task without undue difficulty. Heck, rub the Atoma on there, stone is flat. My 5 year old can do it. I'm not saying that the Atoma is the be all-end all, merely that a larger size plate than stone is not essential to effective, efficient flattening.

What I'm not convinced about is the #120 diamonds on it. It is common for many waterstone users to demand a finer grit diamond plate for their finer grit stones, claiming that coarser grit diamond plates leave large scratches in the stone, which can affect sharpening. Shapton's own loose grit on cast iron flattener includes coarse and fine powder for this exact reason. There's also a valid argument that fine stones require minimal flattening, and a finer medium for flattening allows one to creep up on flat without sending good stone down the drain.

What I'm absolutely not convinced about is the continuous surface of the Dia-flat. Take a look at an Atoma, and the surface is interrupted in the form of small, diamond 'pimples'. The iWood has diamond shaped areas with an uncoated strip between them. The Shapton plates have a dimpled surface. Every flattening 'stone' has relief in the surface to allow slurry to escape. Loose grit on glass/steel is done without pressure so the stone and steel are separated by the loose grit. None of the DMT plates have anything but a smooth, flat area and as such, suffer from stiction as mud locks the stone to the plate. This can be alleviated by regular flushing, and I suspect that the Dia-flat may escape too frequent stiction locking because of the #120 diamonds sticking up rather high. In my opinion, using a coarse diamond to alleviate stiction is not a solution to the problem, even if it does work of a fashion. However once the diamond wear down (as they do), you lose the ability for the plate to resist stiction, whereas interrupted surfaces never lose their stiction resistance, even when severely worn.

Granted, the Atoma and iWood will suffer from stiction, but it's rarely as severe or dangerous as the stiction that afflicts the Duo I have. The Atoma and iWood can be removed from a stone with a little water and a little pulling. Often the Duo 'locks' hard to the stone, that needs a lot of water and effort to break loose. I've dropped a stone on my foot twice because of the Duo, I've never lost control of stone or plate with an Atoma or iWood.

This has nothing to do with the quality of the plate, it's materials or anything else, my critique is purely based on it's design and some experience I have based on flattening several dozen different stone types by several different methods. I have to wonder if whoever actually designed the plate has flattened any more than a few, relatively benign sharpening stones (Shapton Pro/Glass, Norton, King Deluxe) and decided that "Hey, this works on them, all stones are the same so we're good to go!"

If you currently have a Dia-flat and like it, great. If you're buying one regardless of what I've written there, great. Granted, I do sell competition to the Dia-flat in the form of Atoma and iWood plates. I am also actively getting a proper diamond flattening plate hashed out with a manufacturer so anyone out there would rightly believe that I might be biased somewhat. I try to not allow any personal bias affect suggestions to anyone, except when I am 100% sure that by not being quite firm in a suggestion, I'd be doing a disservice to whoever reads what I have written.

I would ask that anyone considering one consider the above carefully. Perhaps I am looking too deeply into apparent 'problems' that don't actually exist in reality. But at the same time, I find that the Dia-flat is aggressively marketed as addressing problems suggested in other plates that don't actually exist in reality either.

I feel I've been too strong here, and do not wish to say anything more about the Dia-flat that could be construed as 'sour grapes' or a blatant attack on a product I feel threatened by as a seller of goods in competition with it.

Again, I'd dearly love to have one, and may (will) actually get one to see whether my fears are indeed justified or simply being overly sensitive after flattening nearly every waterstone commercially available and knowing that no two stones flatten the same, nor as easily as each other.

And believe me, if it's "that good" I'll be screaming it from the rooftops! But it's also got to deal with a few stones that I fear, quite rightly, that will tear it to pieces.

I hope that helps and doesn't raise too many hackles,

Stu.

[Jim Matthews]

TThe Dia-Flat has been as simple and as reliable as a hammer so far.

That's a sharpening technique unfamiliar to me...;)

[David Weaver]

Of all of the comments, #120 grit on fine stones is what I don't like. It's not that it doesn't work, it's that it's not necessary, and the expense isn't necessary, just as it isn't necessary to get a very aggressively priced shapton plate.

Grit at #120 large is only needed on sub 1000 grit stones, and there should be few times a person who is sharpening for a reason other than entertainment would need a 1000 grit stone such that norton 3x glued to something wouldn't do the trick (i.e., restoring a tool). The only one I can think of at all is the need for a coarser stone on japanese tools, where grinding may be a no-no (sandpaper still works, though).

The duosharp and the atoma are probably the two best choices out there for the money if you can manage to resist the temptation to sharpen steel items on them. The duosharp may require a little more water to avoid stiction, but it can handle oilstones, is generally cheaper, and you have a second side that you can put steel on if you like. The atoma is a bit nicer to use, and if you use one a lot, I think is worth the price difference.

I can't think of a stone 1000 grit or above that one or both (atoma may be a bad idea on oilstones unless you use them with dish soapy water) won't work on, unless the stone is a sintered diamond stone.

[Stuart Tierney]

I can't think of a stone 1000 grit or above that one or both (atoma may be a bad idea on oilstones unless you use them with dish soapy water) won't work on, unless the stone is a sintered diamond stone.

iWood and Atoma work on sintered diamond stones too. Not that it's something you want to do often, since the diamond stones are thin and expensive and you're not sending a few cents worth of binder and abrasive down the drain, more like a dollar of diamonds and binder. Not tried the Duo on a sintered diamond stone yet though.

Besides, sintered diamond stones are not exactly common out there in the world.

(For those out there wondering, a sintered diamond stone is a thin layer of diamond rich ceramic material bonded to a thick, aluminium plate backing. Resin type binder versions made by Naniwa and King also exist. They're quite expensive, not even as fast as a decent waterstone, but stay very flat and work with anything you can conjure up. Usually used for polishing/sharpening tungsten carbide knives and precision polishing of production die molds. They are usually supplied with a dressing stone for removing clogging and dressing the surface. 'Flattening' is generally not required. )

Stu.

(Going back to my recently arrived Ouchi chisel pricelist. Very interesting...)

[David Keller NC]

I can't comment on diamond stones used for flattening waterstones. I have 2 duo-sharps, both "coarse/extra coarse", but because I managed to convert one of these to "extra fine/fine" by removing about 10 thousandths of an inch of thickness from a Hock infill replacement blade ("beyond hard" is a good description of Ron's US-made irons), I decided I didn't want to take the chance of scrubbing the diamonds off with a Norton 1000 grit waterstone.

The reason I post this is that, on this one thing only, I disagree with the Schwarz. He notes that SiC wet-dry paper will be very expensive as a flattening system in the long run, and I suppose this is true if one is using the paper to both flatten the stone and refresh the surface, because you'd have to switch to a new piece of paper quite often. In my case, however, I use the paper only to flatten the stone, which means that I've been using the same 8.5 X 11" piece of 220g SiC for months. There's no doubt that the paper is far duller than when it started out, but it is still very effective at flattening the 1000, 4000 and 8000 grit Norton stones, and it's been used for the purpose for perhaps 100 or so flattenings.

The drawback to not refreshing the 220g paper is that you really can't remove a surface glaze from a 1000g stone - the fineness of the dulled grit on the paper removes the surface, but replaces it with another glaze. There's a definite and noticeable difference to the way a 1000g stone feels after flattening with water and a 220g SiC paper on a granite surface place vs. the way the same stone feels if it's been abraded by the Norton "flattening" plate under running water.

But to me, this is a difference without a distinction, because the first blade I flatten the back of will restore the stone's cutting efficiency if I am diligent about flushing it with running water during the process. So the summary for me is that SiC paper is quite a bit cheaper than $125 diamond plates, at least if I guesstimate the life of such a plate based on my experience sharpening hardened steel on diamond plates, and the posts here about how long a DMT plate lasts when used for flattening waterstones.

[Tony Shea]

I for one will never return to the SiC paper on granite to flatten my stones. Not sure how you pulled it off but my paper would never come close to lasting that long before replacing. Must be due to the fact I wasn't using nortons, started that proccess with Naniwa SS's. Have sinced switched to Shapton's and a Sigma finishing stone which is much harder than the Nortons. I currently use a Duo XC for flattening these stones, and have been for over two years now. It is a touch slower now but not by much. This is the only thing the diamond plate is used on and should last another 4 or more years. My only complaint is the coarseness on my finer stones. When I flip the duo over to the coarse side it works terribly at flattening my fine hard stones. There is too much stiction and just doesn't accomplish the task effeciently enough. This is what is holding me back from getting an Atoma 400 to flatten my finer stones. I;m affraid I will be dissapointed with the speed at which it works, as well as the stiction. I would love to get my scratches on my 10000 Sigma to be much finer than they are off of the Duo XC. I have not noticed any negative characteristics on my blades from these scratches though, so maybe it's another one of those real world problems that don't exist. But switching to an even coarser Dia-Flat 120 is just crazy. I would never touch such a coarse stone to my 1000 and up expensive waterstones.

So Stu, how is the Atoma 400's speed compared to an XC Duo on your finer Sigma Power's (10000g)? And is the stiction difference between the two that significant?

[Jason Coen]

But switching to an even coarser Dia-Flat 120 is just crazy. I would never touch such a coarse stone to my 1000 and up expensive waterstones.

Why not? I did it with my Shapton 16k and do it now with my Cho 10k whenever it needs it (which isn't often). It would take an awfully convincing argument to convince me it's in any way a bad idea.

And has anyone else actually used the Dia-Flat plate? It's not the same stone as the XX-coarse, and owning both, the wear properties of the two plates are completely different.

That said, I don't have a dog in all of this. I want sharpening to be as fast and as painless as possible. If there's a better way to do something then I'm all for it. As things stand for me now, the Dia-Flat comes out as the clear winner in the flattening department.

[Dale Coons]

Wow--passion runs high on this topic!:D


That's exactly what I use to flatten the Glasstones I still have in rotation (and oilstones, and the backs of several old paring chisels, and anything else that needs it).


The Dia-flat will work fine on Glass Stones.

....and Chris Shwarz' "Yee-Haw!" endorsement (which now that I re-read seems to cover just about any kind of stone there is)

I appreciate all the posts about different flattening options--they certainly give food for thought. I tried to be very specific in my original post. The DIA-FLAT lapping plate is not the same as any other DIA-(insert product name here). Basically what you all seem to be saying is I can stick with the Dia-Flat and it will work with anything I'm likely to get, be it ceramic, glass or just the plain old nortons I have. If I was in the market for another flattening option I'd give this perhaps more thought. Anybody disagree with that assessment?

[Jay Maiers]

Question for the masses about lapping plate flatness:
How flat do they need to be? +-.001 over the length? .002?

I just bought a DuoSharp and I'm not impressed by the flatness. Placed concave side down on a granite surface plate, I can easily slide a .004 shim under the center of the stone. I'm pretty sure that's not up to their specs, but I can't find a specific number or spec for these anywhere on the DMT site. In any case, I'm going to call them tomorrow and see what's what; I just wanted to get some opinions from y'all.

[David Weaver]

Flat enough that you can sharpen an iron or chisel and have no adverse issues (particularly with preparing the back of an iron or chisel).

It's hard to say how much that is.

However, I have not seen a duosharp that far out of flat. I think their guarantee may be .005" or something along those lines, but if you bought it at a retailer that has a good return policy, you can get them to take it back.

I'd just go order another of the same. It's unlikely it will be as far out of flat...or measurably out of flat at all.

[David Keller NC]

I for one will never return to the SiC paper on granite to flatten my stones. Not sure how you pulled it off but my paper would never come close to lasting that long before replacing. Must be due to the fact I wasn't using nortons, started that proccess with Naniwa SS's.

Yeah, I think that's a good explanation. According to Stu's site, the Naniwa SSs are ceramic, as are the Shaptons. Ceramic (typically Zirconium Oxide) is far harder than the typical SiO abrasive and clay-type binders that would be present in a natural waterstone or a man-made copy such as a King or a Norton. My guess (though I haven't looked it up) is that the Si-C abrasive in wet-dry paper is not as hard as the abrasive in a man-made ceramic stone, so you'd essentially be flattening the paper instead of the stone. ;)

[Jay Maiers]

Flat enough that you can sharpen an iron or chisel and have no adverse issues (particularly with preparing the back of an iron or chisel).

It's hard to say how much that is.

However, I have not seen a duosharp that far out of flat. I think their guarantee may be .005" or something along those lines, but if you bought it at a retailer that has a good return policy, you can get them to take it back.

I'd just go order another of the same. It's unlikely it will be as far out of flat...or measurably out of flat at all.

Therein lies the problem. I have no experience with diamond plates for flattening stones, and have no idea if this is good enough or not. To date, my stone flattening has all been done on the granite surface plate with sandpaper. It works fine with the King stones I'm using, but I hate pulling the stone out of the holder and making a second (huge) mess in order to keep things flat.

The good news is that Amazon is the seller, so there will be no problem returning it if DMT says it's within spec.

[David Weaver]

if it's out .004 and you got it from amazon, exchange it. the next one will be better unless something has changed for the worse at DMT.

[John Coloccia]

My duos are dead flat.

[Stuart Tierney]

Yeah, I think that's a good explanation. According to Stu's site, the Naniwa SSs are ceramic, as are the Shaptons. Ceramic (typically Zirconium Oxide) is far harder than the typical SiO abrasive and clay-type binders that would be present in a natural waterstone or a man-made copy such as a King or a Norton. My guess (though I haven't looked it up) is that the Si-C abrasive in wet-dry paper is not as hard as the abrasive in a man-made ceramic stone, so you'd essentially be flattening the paper instead of the stone. ;)

Not quite.

I call them 'ceramic' because that's what the folks who make them call them.

In actuality, the abrasive is ceramic, which is most commonly AlOx, not as hard as SiC in the W&D paper, but tougher. Stones like Shapton and the Naniwa SS use a resin (or plastic) binder, Sigma ceramic, Bester, some King, Suehiro and a few other use a proper 'ceramic' binder that's pressed into a shape and fired at very high temperature so the binder fuses into a solid mass. There's also magnesia binder, similar to vitrified ceramic, but is hard but brittle (Chosera) and sintered (Sigma Select II) where the SiC abrasive is fired at high temperature and pressure (don't ask exactly how) so the abrasive fuses to itself.

King and Norton and 'old school' type stones (many, generally soft) use a clay type binder which is softer and more readily friable (breaks down).

The problem isn't the abrasive, it's the binder. Softer stones can be flattened with SiC W&D paper because the stone's binder is less durable, and anything that gets lodged in the stone from the paper can also be easily dislodged. The soft paper back on the W&D tends to 'hold' any dislodged particles from the paper which may drive them into the stone. As mentioned, not a really big problem on soft stones.

On harder stone with a more durable binder, the chance of driving a particle of SiC from the paper is reduced, but if it does happen, then it's more likely to stay there and cause problems when you sharpen. Again, the paper backing prevents the particle from rolling and increases the chance of the particle becoming lodged in the stone. It's likely enough that very, very few 'ceramic' stones are suggested to be flattened with sandpaper, and of those that are, they're generally very coarse stones where the sandpaper grit is close to the stone's grit and won't be noticed.

When using loose grit on a hard surface you don't use much pressure to flatten, so the grit is unlikely to catch on the hard base and if by chance it is driven into the stone, it's likely to be dislodged by the other rolling grit particles, so doesn't pose a problem.

Using a diamond plate, the diamonds are held strongly to the plate, and any that do happen to become dislodged are between the stone and a coated, hard surface and are unlikely to lodge in the stone, or if they are, will likely become dislodged by other, still fixed, diamonds.

Sounds all kinds of odd perhaps, but that's what I've kind of worked out why paper is not a good idea for harder stones or those with durable binders, but ok for softer stones. I've done a little testing, and the results are inconclusive at the moment. I don't believe I'll have my opinion changed though, nor will I be recommending sandpaper as "a good idea".

And one should always flatten stones just before they're used and in the condition they're to be used in, i.e; soaked or damp. In that situation, the paper will also be wetted and more likely to become less than completely durable. If you're not flattening your stones in 'ready to use condition' then there's a genuine possibility that you're not actually flattening them at all, since some stones do change shape when wetted.


Dale, You've got the thing already, use it! No need for anything else until what you've got is worn out.

Jay, the thing should be 'flat'. There's no standard per se, but if you stick a good straight edge across it and the slip of light is not consistent at any point, it's not flat and should be returned/replaced. Light will come through between the plate and straight edge because it's covered in diamonds and not smooth, but the light should look the same for the full length, width and corner to corner.

Good luck out there.

Stu.

[David Keller NC]

Stuart - Interesting. I looked up several definitions of "ceramic", and it would seem that the generally accepted definition has more to do with the process by which the object is made (i.e., vitrified at high temperatures and/or pressures) than it does the precise composition. However, one could easily add that a true ceramic is composed of various mixtures of metallic or semi-metallic oxides (that last case takes care of "SiO2", or quartz) rather than (reduced) metallic compounds.

Your post does remind those that are cleaning/rehabbing old stones to never use a highly alkaline cleaner on them, at least in a soaking fashion. Alumina (AlOx), Silica (SiO2), Magnesia (MgOx and MgOH2), and several zirconium compounds are soluble in an alkaline aqueous solution. Many, many household cleaners are quite alkaline, including soap scum removers, drain cleaners, household ammonia, etc... Depending on contact time, one might just remove the top surface of the stone, or might eat away a big proportion of the whole thing.

I should mention to those who would like to try the SiC-on-a-granite-plate as an interim method before spending a large amount of $ on a diamond plate that there are some particulars to my method that might matter according to Stu's post:

1) I don't really use sandpaper in the sense of "paper". The material I use is Klingspor's non-woven fabric-like silicon carbide wet-dry "sandpaper" in 220 grit.

2) I soak all stones (waterstones, anyway) for a minimum of 20 minutes in clean tap water before flattening or using for sharpening. I also soak the paper - doing so hydrates the backing, and allows it to stick very firmly to a granite surface plate.

3) A new piece of SiC wet-dry needs to be "broken in" in that all areas of the paper need approximately the same contact with the stone. Otherwise, you wind up with sharp abrasive on the edges of the paper and not-so-sharp abrasive in the middle. The result is a convex stone - DAMHIKT. This is one reason you want your surface palte to be larger than the sandpaper.

4) Apply almost no pressure to the stone - just enough to move it back and forth and up and down, hold the stone in the middle, and flip it in your grip a few times during the flattening session. Low pressure, changing your grip, and covering the complete area of the sandpaper gives you a very high probability of a very flat result, at least if your surface plate that the sandpaper is bedded on is flat.

5) I frequently rinse the sandpaper/stone I'm flattening under clean running tapwater.

6) Using a coarse grit like 220 seems to have no adverse effects on high-grit-number stones (like 8000's). The surface it leaves is very smooth.

7) Using the afore-mentioned brand/type of paper, I've never had any issues with any grit embedding into my finer Norton/King waterstones, at least that was detectable on the steel surface I was polishing. That said, that may be more of a function of the way I sharpen - at the kitchen sink with running water close at hand to rinse stone/paper. My guess is that you might have issues if you use a washtub in your shop where mixed grits of water stone and wet/dry paper form a sludge that gets stirred up when you rinse your stones.

8) If you're using the kitchen sink, pouring gel-type Drano or the equivalent highly alkaline cleaner down the drain and allowing it to stand overnight before flushing will keep your traps/pipes clear of waterstone mud. I've verified this by taking the drain apart. Not sure what it might do to a septic system and filed lines, however.

One rather interesting idea that's an ancillary to this thread is the possibility of using Lee-Valley's diamond film for waterstone flattening. The potential advantage is faster cutting of harder stones, and matching the diamond grit to the grit of the stone so that a loose diamond or two that gets embedded doesn't matter all that much.

[Eddie Darby]

The lapping plate is suppose to be +/- 0.0005" or as we say, 'half a thou'.
Trend Diamond plates are the same when it comes to flatness.

The flatter the waterstones surface, the better when you are trying to attain sharpness, defined by 2 flat surfaces meeting together, without any reflection of light.

I have a piece of planed walnut, that came off a plane blade honed by one of the sharpening Guru's, that is extremely smooth, and when I sharpen I try to get the same smoothness.
So far it's still a challenge, but having a flat waterstone has helped a great deal in the process.