Kanna Workshop – Chipbreaker Pin

Last time I talked about the general setup and sharpening of a chipbreaker and it’s relationship with the main blade, but that’s only half of the story when it comes to setting up a chipbreaker. There are a whole other set of adjustments and areas to check when it comes to fitting the blade and chipbreaker in the dai, with the main focus being on the pin, also know as the osae-bo 押さえ棒 in Japanese.

The osae-bo is placed in the dai such that when the chipbreaker is tapped in, it becomes wedged between the main blade and pin. Ultimately the location of the pin and the thickness of the chipbreaker determines how tight the fit will be when fully tapped in. You don’t want the fit to be too tight, but it shouldn’t be too loose either. Unless you’re making your own dai, most store bought kanna will come with the pin pre-installed in more or less the correct position, but sometimes you need to make a few adjustments.

Ideally the top side of the chipbreaker (the side that contacts the pin) is usually slightly convex.

The convex shape combined with a well placed pin means that the center off the pin and chipbreaker will make contact and there will be a slight amount of gap on the sides. That’s the most ideal setup for a chipbreaker as it makes adjustment a bit easier since the chipbreaker will pivot on that contact point. Pressure will also be more evenly distributed if the pin is pushing down from the center of the chipbreaker.

The photo below is a bit awkward since I had to hold a light while taking the photo in order to reveal what’s going on, but you can see that the pin and chipbreaker are contacting in the middle and there is a bit of gap on both sides.

Another situation is where the chipbreaker is slightly concave, and only contacts the pin on the sides with the center slightly gappy. It’s not ideal, but it’s not the end of the world. I have several planes with this kind of condition and they still plane well and the chipbreaker does it’s job of preventing tearout.

Even planes from famous makers sometimes come with less than ideal chipbreakers like this one from my Mosaku kanna.

And another from a plane that I bought used…

Here you can see how the chipbreaker abrove sits in the plane and contacts the pin only on the very sides. In spite of that this plane still performs really well.

One more less than ideal situation is when the chipbreaker only makes contact with one side of the pin. You can pretty quickly recognize this kind of situation if your chipbreaker consistenly pivots to one side when tapping it in place. One of the smaller planes that I use on a daily basis has developed this problem.

Having only one side of the chipbreaker and pin touching is the situation most likely to give you trouble. That said I confess I’ve ignored the issue with this particular plane and have continued to use it with good results. I think part of the reason this plane continues to plane well is because its smaller 48 mm width blade is less likely to deform from having pressure applied only to one side.

I share the above images just to show that it’s not uncommon for kanna to come with poorly aligned osae-bo or convex chipbreakers, so sometimes imperfection between the chipbreaker and pin can’t be helped. But if you ensure that the rest of your setup is dailed in, like the quality of fit between the chipbreaker and main blade, you can get away with some pretty wonky chipbreaker/osae-bo situations. In other words if the chipbreaker and main blade have flat ura that mate well (see the last post for more on that), then imperfections between the pin and chipbreaker become less troublesome.

Another crucial factor to this discussion lies with how tight the fit is between the chipbreaker and pin. Personally I’ve come to prefer a slightly looser fit (that goes for my overall approach when it comes to kanna and the fit of the main blade as well). Tons of pressure and tightness is usually not helpful and can introduce weird issues like extra distortion in the dai, and it also makes tapping the blades in and out more troublesome. And the reality is you don’t actually need that much pressure to hold the chipbreaker in place.

With that in mind I’ve come to prefer slightly thinner osae-bo on my full size 70 mm kanna. Full size kanna often come with a 5 mm diameter pin, which is pretty rigid and doesn’t have a lot of give. After a bit of experimentation I’ve started to outfit new dai with 4mm pins instead, which feels more flexible and has more ability to conform. I also think the proportions look nicer.

The two planes below are both 70mm kanna. The one on the right has a 5 mm osae-bo, the one on the left is a dai that I cut and outfitted with a 4mm osae-bo. It’s a subtle size difference and hard to discern in the photo, but in use you can definitely feel the difference. The 4mm pin has a lot more give.

Quick tip: I blackened this pin using a process I learned from a friend here in Japan. The pin is a standard iron rod bought at a home center. After cutting it to length I coated it in a wet mixture of fine clay (sharpening stone sludge also works I hear), then I heated the coated rod up with a torch until it was glowing red, and finally I quickly quenched it in water and washed off the clay. The result is a really nice blackened finish.

The diameter of the osae-bo is usually larger on bigger planes and vice-versa. The full size 70mm plane below has a 5mm pin and the small 42mm plane has a 3 mm pin.

Small kanna come with skinny osae-bo and often they are far from perfectly placed. But the skinny size also makes them more flexible and more likely to conform when the chipbreaker is tapped in.

Osae-bo Adjustment

In the simplest cases where you have poor contact between the pin and chipbreaker the easiest fix is to lightly file the pin. If you want to play it safe you can mark where you need to file the pin, then remove the pin from the dai and safely file it on your bench. Alternatively you can file the pin as it sits in the dai, which gives you the ability to more easily gauge your progress in regards to the fit with the chipbreaker, but you need to be super careful about not running the file into the sides of the kanna or worse yet the throat.

A safety file with one edge smooth helps to safeguard against filing the sides of the dai.

If you take short strokes with the file you can completely avoid projecting the file through the mouth of the plane, but should you choose to live dangerously, then you have to be extremely careful not to let the file hit the mouth of the plane.

If the pin is really misaligned and/or has a terrible fit with the chipbreaker you can pull the pin, plug the hole, and redrill in a more appropriate location. Just be sure to take notes on where and how much you want to move the pin before removing it and plugging the previous holes.

I missed the mark when I first drilled the holes for this kanna’s osae-bo. So I bored out the hole a touch larger, plugged it, and redrilled a second time.

That’s all for now. I’ve skipped going into depth on actually filing and fine tuning the fit between the chipbreaker and pin, but I’ll try to record that process the next time I set up a plane. That said it’s a fairly straight forward process. You just have to take it slow and steady. Make some adjustments to the osae-bo and/or chipbreaker, take some shavings, and if things aren’t what you had hoped, do a bit of troubleshooting to see what areas might need some fine tuning.

Happy planing.