Tearout can be one of the most frustrating problems to try and solve when it comes to using kanna. When setup well kanna can plane even the gnarliest woods without any tearout, but until you understand how to setup the tool well and what problems to look out for, it can be a mystifying trying to get good results.
When tearout happens it’s good to check the condition of the dai, but more often the problem lies with your chipbreaker, also know as the ura-gane 裏金 in Japanese. Most commercially available planes these days come with a chipbreaker, and like every other aspect of kanna, the chipbreaker also requires tuning and adjusting to fit it to the main blade and dai. I’ll do my best to explain my process for setting up a chipbreaker, but it may be somewhat limited. So for those looking for a more in depth look at setup I highly recommend Dale Brotherton’s book Sharpening and the Japanese Hand Plane.
Before diving in, it’s worth taking a quick look at a chipbreaker in action:
This video was made by a group of researchers in Japan, and it’s been floating around the internet for a while now, but just recently I came across it again through Wilbur Pan’s blog. Wilbur generously took the time to have the video translated and updated it with English captions. Definitely worth a look, or 2 or 3.
The video does a good job of covering the important aspects of what make a chipbreaker work, namely the blunted edge/micro-bevel, a tight fit with the main blade, and close proximity to the edge of the main blade.
Now on to setup.
The key areas when adjusting a chipbreaker are:
- Fitting the chipbreaker to the main blade
- Sharpening a light microbevel onto the edge
- Making necessary adjustments to the pin/oase-bo 押さえ棒
Fitting the chipbreaker to the main blade
First things first you need a nice flat consistent ura on the underside of your chipbreaker, just like the main blade. If either blade is not flat there will be a gap between the two when sandwiched together, which in the most severe cases means you end up getting wood chips jamming in between the two.
Once you have the ura-side of the chipbreaker nice and flat you can check how well it mates with the main blade. There are essentially three areas you need to check; the fit between the long edges of both blades (the ura side of each), and the fit between the chipbreakers ears/mimi and the main blade.
The easiest way to check the fit of the ura and how well the chipbreaker mates to the main blade by sandwiching the two blades together with the chipbreaker very close to the main blade’s edge (exactly as it will be in actual use), and holding the two up to a good light source. You can see the process in the images and video below.
When the chipbreaker is simply set in place you an see quite a bit of light shining through. Essentially only the mimi and one corner of the edge of the chipbreaker are making contact with the main blade.
But with light pressure the egde completely closes up. When both blades are actually installed in your kanna dai, the pin/osae-bo will put a fair amount of pressure down on the chipbreaker holding it in place. Doing the light test like this you can see that it really doesn’t take much pressure to get the chipbreaker to conform to the main blade and close up tight. And I’m sure when I install these blades in the dai, the pin will be putting far more pressure than my two fingers here.
Next up you need to test for rocking.
To test the fit of the two simply lay the main blade on a table, and set the chipbreaker on top of it in the same orientation and distance from the edge as when using the plane. From there with light pressure you can press down in the middle of the chipbreaker and tap the corners checking for any knocking. If you have chipbreaker that is rocking, usually it’s the ears/mimi that are easiest to adjust either with a hammer or in some case grinding away material on a stone.
Cheaper chipbreakers, have mimi that are simply bent down. This style can easily be adjusted by pounding the mimi with a hammer on an anvil or the corner of a metal vise.
In the image below you can clearly see the bent mimi on this 60 mm chipbreaker.
More expensive chipbreakers, and those that come with higher grade planes, tend to be shaped rather than bent around the mimi. They also tend to be much thicker at the corners which can make adjusting the mimi with a hammer pretty tough. Let alone the fact that you’ll end up marring the nice surface. For this style there are a few different approaches you can take.
For this Mosaku chipbreaker I adjusted the mimi by removing a bit of material from each on a sharpening stone. Not the prettiest result, but it was effective.
Another example is this chipbreaker that came on a plane I bought used. The corners of this one are massively thick.
The plane was already setup when I bought it, and here the previous owner did actually pound the corners a bit to adjust for rocking. With a few hammer taps they were able to lightly compress the corners ever so slightly (you can just make out the shiny spots of compressed metal on the upper corners).
Lastly one more example is this Keizaburou chipbreaker that I splurged on for a kanna blade that a friend gave me. This is a really beautifully made chipbreaker with nicely formed corners and I was really hesitant to do much grinding or pounding to the corners on this piece. When I set this one up any rocking was very minimal, so I adjusted it by tapping out the edge of the bevel instead. In other words I used ura-dashi to push down the edge to eliminate any severe rocking rather than messing with the mimi.
The Micro-bevel
Once you’ve established a flat ura on your chipbreaker and adjusted for any rocking, it’s time to sharpen it. First you can sharpen the primary bevel like you would any ordinary plane. The goal with sharpening the primary bevel isn’t to create a sharp edge but simply to bring the thickness of the edge down to a consistent level in preparation for honing a micro-bevel. The micro-bevel can then be applied by standing the blade up at a pretty steep angle around 80 degrees or so. The image below shows the rough angle I hold my chipbreaker when honing the micro-bevel. I’m not super fussy about numbers when it comes to bevel angle, I simply stand the blade up until its a bit shy of vertical and then pull the blade along the stone.
If it’s the first time shapening your chipbreaker and no micro-bevel is already established, then you can start with a few pull strokes on a course stone like a 1000 grit. Then move on taking a few more pull strokes on a finish stone (I use 8000 grit). The width of the micro-bevel doesn’t need to be much, and something around 0.007-0.010″ or 0.2-0.4mm should be plenty, but I confess I’ve never actually measured mine. I simply look for a consistent and even line of light shining off the edge. After the micro-bevel I usually hit the ura side of the chipbreaker on the finish stone to remove any large burr that may have formed when honing the micro-bevel.
In the image below I propped the chipbreaker up on a 0.5mm thick scale for contrast. You can see a nice consistent line of light shining off the micro-bevel.
As I was going through my planes and taking pictures for this post, I came across these two chipbreakers with drastically different bevel angles. The primary bevel isn’t super crucial to the function of the chipbreaker. Both of these chipbreakers belong to planes which I’ve used on a variety of projects, and both give me tearout free results. That said, having a shallow bevel on the chipbreaker does make it a bit easier to sight the alignment of the chipbreaker and main blade when looking down into the well of a kanna.
This was a long one, but there’s a lot to cover when it comes to this stuff. I’ll address fitting the chipbreaker to the kanna, and making adjustments to the pin/osae-bo in the next post.
Thanks for reading.
Great article. Thanks for sharing. I wonder how often you sharpen the chipbreaker.
I don’t sharpen it very often, and when I do I usually just do a quick touchup on the finish stone. The micro bevel edge does wear but it lasts for a long time, so the only time I touch up the chipbreaker is if I feel like it’s not performing as well as it should.
Thank you for this series, especially helpful because of the visuals and how (and what) you’re working to achieve. Really helpful for amateur – beginners – like me.
Thanks for your time, so nice to read and learn. In the occidentals ones I don’t have problem if wood is difficult to plane I put very near the chipbreaker and I can finish well, but with the kanna and the some wood it’s impossible always make some holes, I spend a lot of time but it’s really difficult.
In the chipbreaker I make the same shape than the blade I mean the corners a bit round I suppose you make the same, because if not the corners will go up to the edge, it’s like this ?
It sounds like you’re referring to cambering the blade and shaping the chipbreaker to match, is that correct? For standard kanna, cambering the blade is usually relatively subtle, such that it’s not necessary to alter the shape of the chipbreaker. And it’s okay for the chipbreaker to protrude out from the sides of the main blade a bit, that’s actually how I gauge the chipbreaker location these days. I’ll try to post a picture of that in the next post. Also the chipbreaker shouldn’t ever be extending so far from the bottom of the dai that it catches the wood.
Yes, is that correct, because in the occidentals ones I round the corners of the chipbreaker to match the blade, but in the kanna I didn’t know what to do, thanks for your answer and I will left straight and plane again and again until one day hit the bell.
Hi Jon,
I have a question about “shaving ejection”, so to speak. I’ve been able to set up planes with chipbreakers to work well; however, I’ve recently set up a higher quality plane exclusively for finish work and have set the mouth very tight (but not excessively so). I’m finding that it is more difficult in this situation to control the proper smooth ejection of shavings, while maintaining a tight chipbreaker setting when planing wild-grained wood. Because there is less space for the shaving to leave the plane, there seems to be more of a tendency for the shavings to jam in the mouth. I have a feeling that the shaving is hitting the chipbreaker and because of the chipbreaker’s setting/shape, the shaving is returning into the wood of the dai above it and not leaving the dai properly. Do you have any pointers for adjusting planes so that the shavings leave the plane cleanly and smoothly, even when the mouth is tight (and even when it’s less tight, honestly; I’m always impressed at how cleanly the shavings of experienced carpenters leave their planes)? Thank you!
David Wood
Hey David, I’ve definitely run into the same problem on a few occasions. I’ve always found the problem to be too narrow a space between the bevel of the chipbreaker and the opposing face of the dai (koppa gaeshi). On one occasion I setup a new plane and cut the dai myself and tried to keep the angle of the koppa gaeshi relatively shallow, like you might do on a single blade plane. When I would tap in the chipbreaker there was mayber about a 1/16 or a touch more space between the chip breaker and koppa gaeshi but even thought that seemed adequate I had issues with shavings jamming. On that plane I experimented with lowering the bevel angle of the chip breaker, making it really steep like 23-25 degrees. That opened up the space a bit and defintely improved the situation. In other cases I’ve had to shave a bit of material from the koppa gaeshi, widening the angle a bit, to give more space. I feel like the biggest problem is when the space between the chip breaker’s bevel and koppa gaeshi is more or less parallel. If the space tapers such that it opens the further shavings travel, then shavings tend to pass much more freely without jamming. Figured wood and woods where the shavings have more of a tendency to break up and curl as they pass the blade definitely exaccerbate the problem, but as long as you give enough clearance you should be able to start getting good results.
Hope that helps a bit.
Jon