Saturday, September 27, 2014

SK-11 diamond sharpening stone and some $store surprises

Planing away, hard at work building a deck, I am having some issues with edge retention. I don't know what it is, but there seems to be one board in this batch that has some serious abrasive qualities. It's like it's filled with sand or something (not that living at the beach has anything to do with that, or.......).

You see all of those nicks? They weren't there a few seconds ago. In any event, it's time to sharpen. Again.

First, a surprise.

The other day, I was wandering the isles, looking in some unlikely places for some diamond grit abrasives (More on this later). While I was at the $Store I found, of all things, a sharpening stone.

How bad could it be? For $1, expectations are low, but I was actually quite surprised. This thing works! I soaked it in water for a minute and used it like a waterstone. One face wasn't perfectly flat, and it is a touch soft, but....... This bugger cuts! 6"x 2"x 1" of steel eating fury! This blade is one of the hardest ones that I own, so the speed is even more impressive.

With two faces, it is ostensibly a coarse/fine combo, but I didn't see much difference, to be honest. The coarse side is softer than the fine. It is noisy. Crunchy sounding. The coarse side is soft enough to make a little bit of mud, which seems to speed the grinding action.

Did I mention that it is soft? Being soft, it will require regular attention to keep it in the realm of flatness. I need two.

There is an antique mall/ flea market kind of place here, and way in the far back corner, there is a booth that sells tools. The cheapest of the cheap, but I've found some decent stuff there. They ALSO have some sharpening stones, and they're even cheaper than the $Store.

I splurged and got the big 8"x2"x1".

$0.75 (The 6" one was only $0.60, haha!).

Like the smaller stone, one face is slightly dished, but only by  .15mm.

The cause of the dishing is a bit of a raised lip around the perimeter, a remnant of the molding process.

Bevel the edge, and it will be almost perfect.

The other face is as flat as I can measure. A 0.038mm feeler won't fit, and that's the limit of my measuring tools.

Good enough for me. It will go out of flat in use, anyway.

This stone is harder than the one from the $store, more like a traditional oilstone.

Being harder, it is also slower. It is possible that using this one with oil would improve its action. This stone wouldn't have any problem with your average western style mono-steel blade.

The fine grit side would bring the blade to a near-mirror finish, given enough patience. The softer expensive ($1!) stone has spoiled me!

I never would've thought that the $store would have sharpening stones, much less ones that work. I've been looking for a coarse grit stone that works tolerably fast, and this one is nearly as quick as using the belt sander! Now if only I could find one in a 8"x3" size......

The ura on this blade is starting to encroach on the edge. Time for a little bit of ura-dashi.

A new weapon in my fight for flatness, an SK-11 diamond grit sharpening stone, bought from eBay seller: Sakura*pink. The stone is targeted towards  the Japanese market, but is made in China.

I've bought from him before, and he has always been patient with my utter lack of Japanese language skills, helpful in finding stuff, and very good at getting the best shipping price (and refunding any extra!). A great seller!

The stone is 204x65x7mm, and VERY heavy. It's over 1/4" thick.

The embossed pattern is #400 grit one side, #1000 grit the other.

The #400 grit side is flat. The #1000 shows a bare sliver of light under the ruler, but the gap is less than I can measure (so less than 0.038mm). Both sides are absolutely flat along the short axis. This stone is light years flatter than any american made diamond stone I've ever owned.

I want to focus on just a small area. It is easier on the blade (and me) if I do a small bit frequently, rather than waiting until it becomes a large endeavor.

The ren-tetsu is nice and soft, making ura-dashi fun. Just this little bit of tapping, using my modified track hammer, displaces the soft iron and pushes the hard steel down.

Sighting along the cutting edge, you can see that the edge has been deformed, resulting in a small bulge to the left.

The bulge gets ground down. That's why I bought the SK-11 stone.

These stones have a reputation for being only a short step down from the Tsuboman Atoma stones, and at 1/2 the price (or even less. Sakura-pink sold me this one for $35! A great guy!). This is what most of the Japanese guys use, particularly for waterstone flattening.

With judicious tapping, I am gradually evening out the flat area, just back from the cutting edge. 

Each time I do ura-dashi, the shape gets a bit better.

On the bevel side, the hammer marks show how the displaced iron actually pushes the steel down. You want to do ura-dashi before grinding the bevel, sharpening the blade.

From this point, it's sharpening as usual.

Ura-dashi adds some extra work to the sharpening process, but the new diamond stone works quickly. The finish is still rough, much coarser than the grit numbers indicate, but that should mellow with use.

The quality of the SK-11 stone isn't perfect, but it's pretty darn good, MUCH better than I was expecting, and far flatter than anything made in the good 'ol USA. I plan on using this stone with the lightest touch possible, in hopes maintaining its speedy cutting action. Most important to me, though, is that it's flat. Why can't WE make good stuff?


  1. Hi Jason,

    Nice to hear the opinion of somebody with experience on american made diamond stones. Seems east is the way to go.

    Did you find the coating of the stone to be "thin"? I don't know how to express this, but I do feel a difference between the coating of this stone and the cheaper Chinese we've been talking about. Or is this electro coating thing that makes them not so bulky?

    Other question, how many grams is your hammer? looks kinda heavy.


    1. Hey Sebastien!

      Hammer details to follow......

      The american made Eze-lap stones have the heaviest coating, while the DMT offerings are very thin. These SK-11 stones feel right in the middle, in terms of electroplated film thickness. The OTHER Chinese sharpening stones that I've been obsessing over, seem to have a coating that is on the thin side, too. Thinner than the SK-11, comparable to the american made DMT stuff, I am guessing.

      I tend to equate film thickness with durability, but that probably isn't the case. Maybe a generalization? I don't know. Eze-lap is very durable, while DMT is not. My REALLY cheap $4 Chinese diamond stones seem to be lasting at least as long as the DMT as well, so it can't all be about film thickness.

      As you know, I've been messing around with diamond coated finger-nail files, as a cheap source of detail files. I found some thin coated ones that worked a little bit, while a different one, that had a much thicker coating, peeled off like paint. Maybe it was paint, and not electroplated at all!

      I haven't heard anything negative about these SK-11 stones, and I hope that they prove to be durable. They *look* a little thin, but...... We'll see.

    2. any update on your stone after a year? mine has reached the buy a new one point, but I think it was due mostly to my improper cleaning after use.

    3. No news at all I'm afraid.....but I'd love to hear how yours has faired, having likely seen more use than my poor, neglected sharpening stones. After moving to Hawaii last year, I've not needed to use it even once, while your stone has likely seen some hard use from those students of yours. Bearing down heavily is hard on those diamond stones, but something that we all do when we are learning.

      In general terms though, I've found that the soft iron used with laminated blade construction is brutal in its treatment of diamond coated sharpening stones. The soft iron (or mild steel) tends to grab the minute particles and rip them loose from their substrate. After a while, you are left with a diamond sharpening stone that doesn't seem to have many diamonds. I suspect that some of those dislodged diamonds tend to find new homes in waterstones, leaving mysterious coarse scratches, right where you want them the least. I think that using a well worn diamond stone for waterstones flattening entails a calculated risk. Keep a new diamond sharpening stone FAR away from any other waterstones you might have, haha.

      Nowadays, if I need to reset a bevel on an old kanna blade, I use a file to remove the bulk of the soft jigane, then use a diamond stone for the hard hagane. It's faster and saves wear on the expensive diamond stone. The downside is that you loose the base, making freehand sharpening more difficult.

      Coming back to these old posts is interesting (and a little scary as well). I've got a lot of updates that I could write.

    4. I don't use diamonds on my blades anymore, only cheap chinese to sharpen stanley blades and scrapers or cold chisels. For restoring old blades, thing seldom done nowadays since julia offered divorce were I continue buying planes, I go directly to the cool grinder of mine. If the geometry doesn't need to be corrected I just hollow ground at different angles 1mm under the edge, the idea being making a such a minute hollow that can be taken off fast with the 800 king, my coarsest stone atm.

      I haven't feel any diamond particles on my waterstones, but when I tried using brazilian norton sandpaper last time in the south, the result was a catastrophe, the 3000 stone full of black dots.

      I will try to make a drawing of the hollow grinder I mean, since I think the description is not that good. And as soon as I arrive I take a picture of the diamond stone and the saw blade we talked about a few weeks (or was it months) back.


Like all of us, I am figuring this out as I go, so when you see something that is incorrect or flat out wrong (and you will!), let me know. This is a learning process. Real people and names, please. Constructive comments and questions are very welcome, but hate speak/politics are not! Life (get one!) is too short.

Thanks, Jason