More thoughts on ura-dashi (tapping-out a Japanese plane blade)

A few points that I want to emphasize here. I'll step back .....



For this round of ura-dashi, these marks are all of it. What is that, like.... 20 strikes, maybe?

I am using a light hammer. My "anvil" is a lead filled can. I like that the lead is soft, because it cushions the blade. A chunk of hard metal works great, but feels..... Hard and slippery. The blade slides around more. A chunk of dense wood works well, too, but cushions a little bit TOO well. It will require more force from the hammer.

A turning point for me, was realizing that I WANT to make dents in the bevel of the blade. I want the sharp little edges of my hammer to dig in, and actually move the metal around. I am striking the blade pretty lightly, but because the hammer digs in, very little force is required.

I had read dozens of times about supporting the blade, using the face of the hammer obliquely, hit in the thicker 1/3 of the blade, don't hit the hard steel part, etc etc. My error was thinking that ura-dashi was a "bending" process. That you are hitting the end of the blade, to "bend" the edge down. You read of others having the same mis-perception, and wondering why they are having problems.

I forget where I first read about a "good" description of ura-dashi, but the essence of what you are doing is this.

• You hit the soft iron
• You create dents, that cause the surface to expand
• The expansion causes the end/edge of the blade to deflect downward.

The anvil backing is nice to have, but you could actually do this on a flat surface (in theory, although I wouldn't want to). As soon as I stopped thinking in terms of "bending" and started thinking about dents and displacement, it all came together. After that, ura-dashi became fun and relatively simple.

I think that this line of thought needs to be emphasized more. 

It is difficult to see, but there is a little bump that protrudes to the left, and right under that, a dented area on the face of the bevel. The dented area looks like a smudge, or hazy spot (among the dust specs). Hitting, way down on the bevel, caused the metal to deform all the way at the top of the blade. That's pretty cool!

The amount of distortion is made evident while grinding.

Even though I was striking in the middle of the bevel face, the effect is amplified, and spreads clear to the edge. The picture above shows that even after a fair bit of grinding, the dented area remains. Small, well directed taps can give big results.

In this case, I am only focusing on that little bit, the zone in the bottom center. I eventually hope to get the entire edge to look like a flat line.

I am trying to sculpt a straight line, only shaping a minimum amount of metal. Something like this would be ideal....

Mandara-ya has the REAL info!

And again, wrought iron makes this a LOT easier! This blade.....

...needed a lot of work to hammer out the back hollow (urasuki). This blade is made with normal, soft iron, NOT wrought, and it was MUCH more difficult to move.


MANY little hammer strikes.

I am striking at the thicker portion of the blade, trying to affect a large area and volume. This is heavy shaping, and a skilled practitioner would use a large hammer.

The result was acceptable, not perfect, but...

The upper blade, not the lower.

Why bother?

Good blades have VERY hard steel. Now that we all have access to cheap diamond sharpening stones, the question of whether ura-dashi is worth the bother, seems moot. Not so, not so.

The blade is all important. Each blade is different, and the wooden dai is cut to fit the blade perfectly. If you change the shape of the blade too much, the fit will be ruined.

A different blade.

This is a blade that has probably never had ura-dashi performed on it, ever. The lighter colored areas represent steel that has been removed, effectively changing the shape of the blade, causing it to fit poorly. This is a blade that will not work as well as it could've.

What happened with this kanna, is that the blade essentially became thinner, and therefore fit loosely. To tighten things up, the user needed to add a thick paper shim to the blade bed. This works.


A better solution would be to preserve the original shape.

Worse than a sloppy fit, a bigger problem is that if you don't do ura-dashi, you might run out of steel.

At the outer corners of the blade, the steel is getting thinner. Some blades will show the steel nearly disappearing. You see this problem on chisels, too.


Another blade. This one was owned by someone who took care of his tools.

The urasuki is getting very small, but still maintains its proper shape.


When you look to the bevel, you can see that the line of hagane is even, and of full thickness.

The longer one might not last as long as the shorter of the two.

This kanna looks old, but has seen little use.

The beautiful blade was forged by a very talented blacksmith.

 Look at how thin the steel is! The owner of this tool needs to be VERY diligent in performing ura-dashi. This is a high end kanna. Very nice!

It's not that hard to do. A little hammer with sharp edges.....

My ura-dashi hammers

I'm just looking for any excuse to not do what I should be doing, which is working on the house. We are relocating to Hilo, Hawaii in just a few short months, and there are a multitude of loose ends to tie up, before we rent out our house.


My friend tsuresuregusa wants more details of the tack hammer that I use for ura-dashi.

This is a little tack hammer that I picked up at a thrift store/junk shop for a couple of $'s. One end of the head is split, to better hold small tacks (at least I *think* that is the reasoning). The split end is the face that I use ( I would prefer that the face were NOT split, but......). The most important detail is that I filed the faces to have sharp corners. This allows the hammer to really dig in, making nice tiny divots in the metal. A smooth face will tend to slip. I want something that will grab and gouge!

173g total.

It is a small, but precise tool, and makes ura-dashi fun, rather than nerve wracking. It's so much fun, I do chisel blades, too.

I have another hammer head that has been patiently waiting for a new handle.

This little guy has forge welded inserts on both faces, and one end comes to a nice sharp wedged shape.

Looking for guidance.



This is on my wish list, maybe not this exact hammer, but something in this style.

Pro Shop Hokuto has style

A funate genno with a good sharp end. This would be just the tool, for those hard to convince kanna blades.

The process of ura-dashi is made soooooo much easier if the kanna blade is made with ren-tetsu wrought iron. The soft iron works very easily, helping you to shape the blade as you choose. Less force is required, so there is less likelihood of grievous mishap. A regular soft iron backed kanna blade seems to require at least twice as much force. Wrought iron...... It's about more than just good looks.

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?