Saturday, October 18, 2014

Setting the chip breaker blade on a Japanese plane

We are moving to Hawaii, and with only a few short weeks remaining between now and the big event, I've been very busy. Building stuff using tools, as opposed to just playing with the tools themselves. And planing...... Lots of planing.

A few days ago, I was watching a YouTube video. I'm gonna warn you now. If you just love watching someone work (using Japanese tools), these videos are great.


It is a demonstration from a European woodworking event, and the sound is terrible. Not much is happening. It is long (1/5 is 45 minutes!).

If you want to watch, great! But this has been in my "watch later" list for nearly 2 years now, and prior to this, I only got to about 15 minutes before giving up. Well, a few days ago, I was in serious need of watching someone else work, and.....

Way in there, maybe around the 35 minute mark, there is one little tidbit of knowledge that I had been missing until now.

Do you ever feel like you are the last guy to arrive at the party? Surely all of you Japanese kanna enthusiasts already know this one, but in the off chance that you don't...... I've never seen this presented before.

When I am using a single blade kanna, I get long, thin shavings that actually leap from the throat of the plane. For someone used to western style planes, this is alarming the first time that it happens, and it's really fun!

When I use a double blade kanna, the shavings still make that amazing *Riiiiiiippp* sound, but the shavings are almost always curled forward, into little tightly rolled shapes. That is due to the "chip breaker" effect of the Osae-gane back blade, compressing the shaving as it comes off of the main blade.


Those Japanese carpenter's kanna don't do that, though. Even their 2 blade kanna send off those self-propelled shavings that I love, so what am I missing?

This is one of the old beater kanna that I fixed up a while back. There is something about the composition of the steel, the tempering, something. For whatever reason, the blade holds an acceptable edge for a very long time, and it is quick and easy to sharpen. It isn't suited for the finest work, but it is providing good service as a rough/jack plane, and I've been using it a lot.

The blade bed is uneven, so I fine tune things a bit,  using Super-glue to tack down some thickish wood shavings.

It doesn't take much. The shaving is translucent, but is thick enough to give the main blade a little more lateral stability.

Because there is a big hump right in the center of the bedding surface, the main blade had a tendency to pivot, and the poor support translated into cut instability.

The little bit that I glued onto the right hand side helped greatly. It is the slightly cleaner strip on the side. Most of the bed is still scraped clean (although blackened and dirty looking).

What I am *really* working on is the fit of the back blade/secondary blade/chip breaker. The Osae-gane. This one was too tight, and with the main blade rocking and rolling, fine adjustment was difficult. It worked just fine, but I want it good...... REALLY good!

The Osae-gane needs to be set close to the cutting edge of the main blade. How close? As close as humanly possible!

0.1 mm is a good number, but how do you know? If I hold the kanna upside down and tilt it just right, I can get a glimpse into the throat.

 "Say Aaaahhh....."

Underneath the white horizontal line of the throat opening, you can see the sliver of main blade that is exposed. This is as close as I can get. Any closer and I can't see what is happening. I thought that this was good enough.

Not quite. This is probably close to 0.3mm.....I want 0.1 mm. So, back to what I learned from the video.

If the shaving curls forward.....

... tap the Osae-gane down, closer to the cutting edge. Small taps.

Tiny tap....

Sooooo close.

Itty-bitty tap.....

Bingo! Notice the soft sapwood on the left, the denser heartwood on the right. The shaving is perfectly even in thickness. Cool!

Hilarious! A kanna rooster-tail!

When properly adjusted, there is a very sophisticated interaction between the body and blade of the plane. The Osae-gane stabilizes the main blade, but it also conditions the wood shaving as it leaves the cutting edge. These shavings are only rigid for a few moments, before turning all limp and drifting away (or getting *in* the way). The shaving is NOT just getting thicker due to increased downward pressure on the cutting edge.

So.... Funny looking wood shavings are great and all, but the important thing is that tear-out is greatly reduced. 0.3mm was good enough for a flawless finish on an easy wood like pine, cherry, or walnut......but this Port Orford cedar can give me fits. Even stuff with perfect grain can blow out in the most unsuspected areas. Maddening!

This piece is flat grain, so diving/rising grain, combined with a handful of tight knots.

I can plane diagonally. I can zigzag back and forth, changing directions in the middle of the cut.

There is a little fuzz, but no big chunks are missing.

This is exactly the type of thing that would've been causing major problems before. The finish would be perfect, had I not gone too far in adjusting the Osae-gane. I overshot the edge a couple of times while trying to get some decent photos, messing up the main blade.


This was a big piece that was missing from my puzzle, I just didn't know it.


  1. This is awesome, thanks for sharing! I've been trying to understand the conditions for the shavings to shoot out in that amazing way. Every once in a while I would accidentally get it, but could never reproduce it consistently. Chris Hall alluded to how to make it happen in an old blog post but I still couldn't figure it out. Will definitely give this a try.

    1. Hey Siavosh!

      I was wondering if you would catch this one, haha! This is a whole 'nother level of finicky, but it's really quite amazing.

      I've got no secrets, but but I sure have lots of questions. Knowledge not shared is swiftly forgotten and everything that I do know was first put out there by someone else. I'm just passing it on.

      I hope that your kanna are treating you well.


  2. Jason,
    You're moving to Hawaii? Wow! What does your wife do? Why are you moving?

    I remember Robert Meadow used to explain to students that the name "chip breaker" was actually a misnomer for Japanese kanna. The sub-blade is actually a better name because it actually pre-stresses the main blade right out at the cutting edge more than it breaks the chip. He explained that when you get chatter with a plane it's because the edge of the cutting blade gets pushed back by the wood being planed and then it springs forward and this repeats over and over again. The sub-blade gets a secondary bevel at the edge so that it is "stronger" right out at the edge than the main blade. It pushes the main blade back essentially pre-stressing it so you do not get that chatter. In order to do this well it needs to be right up tight to the edge of the main blade. I will never forget Robert explaining this. Good luck with the move!

    1. Hi Dave!

      Yes, towards the first half of December (holy crap holy crap holy crap!!) we are moving to Hilo, Hawaii! My wife accepted a post-doc position at University of Hawaii, Hilo as a project coordinator for a multi disciplinary study on a whole bunch of different species. Her field is genetics, focusing on evolved organic sensory mechanisms used in navigation. At least that's what I *think* she studies. It's all so over my head, my eyes cross every time I see a string of letters that represent an expressed DNA strand....... Ohhhhh, my head..... It hurts.....

      The utility of the sub-blade is clear to Japanese kanna users. Heck, a few years ago even the WESTERN plane users started using their chip-breaker again, after that Japanese video went mainstream, showing how the "breaker" caused the shavings to release without tear-out (or just take a super thin shaving. That prevented tear-out, too.)

      What was funny (for me) was that I thought that I was already there. I thought that I was close enough! I was getting great results with pine and cherry, just not the typical "difficult" woods like the sapwood of cedar, or rowed mahogany. I was trying to achieve better results, but had more or less given up on the tough stuff.

      I literally cannot see the exposed portion of the main blade anymore, but the shaving tells all. It gives an immediate verification that the blades are set correctly to each other, without having to shred some unruly grain for proof that I DIDN'T get it right, haha! Not that I've eliminated tear-out, mind you....

      For the REALLY difficult stuff, your higher angle kanna still works better, even though I have yet to fit the sub-blade. Fitting that has now jumped to the head of my "do" list. I just wanted to thank you again. It is a good one!


  3. That's interesting, genetics has been a bit of a hobby for me over the past two years or so. I have read a few books on the subject and find it very interesting. I also have a daughter working on a PhD at present. I hope everything works well for you with the move and that you like Hawaii (although I am not sure what's not to like).

    I'm glad you are getting some use out of that high angle kanna, if I had kept it, it would just sit for years. It's better that it gets used. Take care.

  4. Another golden nugget. Sometimes I think I don't run across a piece of knowledge or technique because I wasn't ready for it. Surely, I thought, if I can't even see the chipbreaker edge its close enough. I've seen video of a temple carpenter finish planing structural beams and laying the 20' long flat shavings to the side. But how? I shouted when I finally tapped the chipbreaker down far enough and the shaving suddenly jumped out so gracefully. And more importantly, the reduction in tear-out is tremendous. No more blowing out grain finish planing assembled rail/stile connections. Thanks!

    1. Hi Gabe!

      It looks like the original YouTube video has disappeared, and there you go....something else has been lost!

      Knowledge is funny that way isn't it? This tiny piece of it came to me exactly the same way. The original video was horriblely boring, but there was this point in the demonstration where the daiku was setting his kanna for the cut, and the shaving was curling. He kind of looks out at the audience, seeming to be thinking "Surely you guys already know this but......well, then again, maybe you don't ".

      I too had read all the books/websites/blogs and videos, but that particular moment was the one for me. Until then, I just wasn't ready.


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