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I’ve always preferred diamond plates for flattening my waterstones and oilstones. Though a coarse or extra-coarse diamond stone does a fine job, the sharpening stones are pretty hard on the diamond impregnated surface, wearing the diamond plate prematurely, according to engineers at DMT.

I’m not a big fan, however, of the stone-based flattening systems I’ve used. I have yet to use one that stays flat enough. I have purchased two of the Norton flattening stones. Both were warped to the point of being unusable. After I flattened them (with a diamond plate!), they went out of flat after only a few uses.

I like Norton products. Lots. But not this one.

So I decided to flatten the product one more time.

Back in January, the president of DMT sent me a prototype of a flattening plate called Dia-Flat that is impregnated with diamonds at 120 microns. The diamonds are bonded to the plate using a proprietary technology called DMT Hardcoat Technology. They asked me to use the heck out of it and report back. So I used it. This is my report:


I’ve taken the stone with me all over the country these last few months and let students flatten all their oilstones and waterstones and who-knows-what stones. At Roy Underhill’s school some students brought in all their stones from home. We flattened every oilstone we could get our hands on in Roy’s shop.

And I’ve flattened my Shaptons about 200 times with the stone. So far, I love the thing. It is heavy, at four pounds, and big, at 4-1/4″ x 10″. The weight and size keep it on the stone and make it easy to hold.

The grit cuts fast and leaves a nice surface. And the thing is flat. DMT certifies it as flatter than .0005″ across its surface. That is way flatter than anyone needs.

How does the Hardcoat hold up? No clue. But Stan Watson, the technical director at DMT, is still using the stone from R&D on the product and says it is “far from worn out.” The Hardcoat technology is the real curious thing here, and I asked Watson about it in an e-mail.

“…(W)e went back to the drawing board with a clean slate and looked at ways to increase the life of a stone designed for the tortuous application of flattening another abrasive stone,” Watson wrote. “After several attempts, we devised a highly proprietary process that adds significant wear resistance to the matrix used to bond the diamonds to the steel substrate.”

So what is the coating made of?

“Sorry I can’t go into more detail about it,” he wrote. “Even Coca Cola has their secrets!”

DMT introduced the stone to the public last weekend at the Northeastern Woodworkers’ Association Showcase and will be available shortly – right now DMT is just working out the details on packaging and marketing.

The price? The suggested retail is $199.99, but Watson said that most retailers will discount it below the suggested retail.

I plan to buy one to replace my DMT Duo-Sharp stone that I have been using for 10 years. It still flattens my stones, though it is now quite slow.

We’ll see how the DMT Dia-Flat holds up, and I’ll report back in a couple years.

— Christopher Schwarz

Sharpening Sources
• A good source for sharpening supplies, including DMT, is

• Ron Hock’s book “The Perfect Edge” is a great reference book on the topic.

• Want to learn to sharpen on sandpaper? Try Brent Beach’s site.

Product Recommendations

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Showing 32 comments
  • Tony-Memphis

    I’ve read that this plate is too coarse for fine stones like a Norton 8000. Has anybody tried it on a fine stone liek that? Did it work ok? I currently use a DMT “Black” stoen with the dots (not sure which line that is). It works ok, but it is small and I’m not sure how flat it is.



  • HowardS

    I’ve been honing all kinds of tools for more years than I care to remember and I consider having a flat hone to be at the basis of getting a perfect edge. I’ve tried all kinds of systems from iron lapping plates with Clover Compound to the DMT D8C and, of course, the Shapton DGLP. The flattest is the Shapton and it is also the most expensive. It’s warranted for Shaptons in order not to void the warranty. For other stones I use the D8C now. It’s coarse enough (325 grit) so that it doesn’t load while lapping a stone and pretty flat. It’s good for natural and artificial waterstones but oilstones tear the diamonds out. Soooo, I was at DMT yesterday and learned of the new DiaPlate product and am anxiously looking forward to it. I share your dislike for the Norton Flattening stone but carry them nonetheless as some people insist on it.

  • jaap

    I wonder why you all use those daimondplates just to flatten waterstones. I use a Trend fine daimond plate as my first stone together with an Eclipse holder. Most of the times 10 strokes do the work. Then on to an 8000 naniwa and a final stropping with some Flexcut paste on a piece of wood. Very quick, very fine edge and scary sharp. Only one stone to keep flat; for that I use a naniwa flattening stone (looks like the norton here) and some carborundum powder.

  • KC Kevin

    If I’d known you were flattening waterstones, I’d have brought mine with me when you were in town a few weeks back.

  • KC Kevin

    If I’d known you were offering to flatten sharpening waterstones, I’d have brought them with me when you were in town.

  • jsilverman

    anyone else take the “cheap-road” for flattening waterstones– sandpaper on glass or granite???

  • hallamjeff

    Yes! I too loathe my Norton “flattening” stone. It hasn’t done the job, and it often left really coarse bits in my fine stones.

    I am going to follow your lead on this one and end it’s existence.

    Thanks for the heads up on the new DMT product.

  • chayward

    Funny video.

    As to the complaint about the flattening stone not being flat. I agree. Mine wasn’t and it caused me a few headaches until I realized it wasn’t flat.

    But just like your jack plane does not have to be flat to flatten a board, the flattening stone does not have to be flat to flatten a honing stone.

    After drawing the standard pencil lines all over the stone to be flattened, move the flattening stone in lengthwise strokes at 45 deg to the honing stone moving up and down the stone with each new stroke (just as you would when flattening a board). The turn 90 deg and repeat (as you would when flattening a board).

    Repeat this until all the pencil marks are gone. (In fact you can even go all Moxon here and traverse the stone if you like.)

    Then align the two stones lengthwise and take lengthwise strokes. Begin on one side of the stone and take each stroke about 1 inch further across (widthwise). About five strokes is good here.

    Dry off your honing stone (paper towel) and check for flatness against a light (with the same cheap flat rule use use for the ruler trick). You can’t check flattness if a stone has water on it.

    It has never taken me more than a couple of repetitions to get a stone flat using this method (and multiples are only needed if you’ve been hollowing out your stones sharpening scrub planes).

    And for my money a $26 dollar flattening stone beats a $200 dollar diamond plate

  • Greg68

    How does this new product differ from DMT’s D8XX diamond plate? This one retails for $84.99 and can be purchased to less at some retailers.

  • Dean

    Chris, did anyone from DMT say if the diamonds on their plates are “monocrystalline” or “polycrystalline”? Lee Valley has a sidebar on page 91 of their September 2010 tool catalog talking about the superiority of the monocrystalline diamond plates. I’m guessing at $199 it’s probably a monocrystalline, but was wondering anyway.


  • damien

    Is cycling between stones not a better alternative to a hammer? “These surfaces will always be flat if you are using three stones in rotation” Leonard Lee in Sharpening, talking to the poor and parsimonious (being those without a girls best friend).

  • Wood Zealot

    I hate to be a critic of technique but you forgot to soak the stone in water first.

  • Ben Lowery

    One thing I do like about the existing diamond stones from DIA for flattening is the handle attachment. When you get a 8000 grit waterstone close to flat, the suction is pretty amazing. I’ve seen that the Shapton flattening plate includes channels to help prevent the suction; does this new offering have anything similar?

  • lbjhb

    How come the Schwarz site out performs the editor blog when there are now four people inputting? Keep up the good work. Always informative and entertaining.


  • rwyoung

    Face-shield? We don’t need no stinkin’ face-shields. It’ll be just like shooting womp rats in Beggar’s Canyon back home!

    (Apologies to Mel Brooks, George Lucas and anybody else who might get their geek gland in a twist.)

  • Andrew

    Not a fan of the Shapton Diamond Lapping Plate? I’ve been using the a DMT to flatten my stones as well. It looks as though the edges on mine have lost the diamond coating between the flattening of stones and flattening of a vintage 1 1/2″ chisel I purchased from Walt. Maybe I should check with DMT…

  • mpn77

    Next time i’m in the shop, i’m going to take a hammer to my Norton flattening stone as well. That looked like a good time.

    That thing is the worst. After i bought it, i instantly became discouraged with sharpening, and ultimately the results i was getting with my hand tools. I made the mistake of assuming that something labelled “flattening stone” would actually be flat itself. Once i took a straight edge to it the clouds parted and the rays of schwarz-like clarity filled my shop. My flattening stone was concave and making my course stone convex, which then made my fine stone concave. Inverted camber with very nicely polished edges isn’t what you need to plane effectively! Ever since i moved to grit on a glass plate life has been good (but maybe a little tedious).

    Anyway, really hate that product and can’t wait to smash it.

    Any idea where the DMT plate will be sold?


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