I dediced to take a break from the fuigo build to make a hikouki kanna. Actually what happened was that I’ve become really tired of the intense morning light that shines through my shop windows. I want to make a set of screens to cover the windows, but had told myself I wouldn’t do any more shoji work before making this tool, used to accurately plane thin strips of wood to thickness.
Odate refers to it as Kumiko-Kezuri-Kanna, and there are western examples as well, but if you’re looking to buy one online its ‘hikouki’ kanna. Just a touch expensive.
Des King references it as well: Hikoki Kanna, although as he mentions in his book on shoji, he thicknesses kumiko with a bench top drum sander before a final finish planing. I suppose that’s both fast and accurate, but I’m not yet at the point of needing such a machine.
This is what I started with to thickness kumiko. Its a very cheap 50mm kanna from Tools From Japan with home made runners on the bottom that determine the finished thickness. Its a small plane, so I can only work one piece at a time.
The problem with that is wood moves. When you cut thin strips, they’re going to warp a little. This is a picture of some 1/4″ Hemlock kumiko, the worst warping off the saw that I’ve ever seen. It was a shame too because the board had such nice tight grain. When you go to plane warped material to thickess it wants to flex up off the planing beam and push into the cutting edge, even when the depth has been reached on the bottom runners. The result is a lack of dimensional control. I’ve resorted to finish planing each piece with a dial caliper to check in several places along the length of the piece being worked. With care and attention its possible to keep things within a few thousandths of an inch, but terrible slow and tedious.
Consider that Odate relates how his master could plane kumiko to thickness by touch alone. Obviously I have much to learn, but in the mean time there is a better faster way.
Cut the dai. I’ve blogged about the process in an earlier post, Making a Dai. For this second dai I used ink on layout, and added a center line to the bottom and top of the block. It measure 11″ in length, and was built to fit the one large blade that I own, and change among various dai. I’m really getting my money from this blade!
I also used a center drill to start the holes that house the sub-blade holding pin, no worries of drifting off the mark like last time. Placing this hole still feels iffy to me, thankfully the sub-blade has a forgiving amount of flex to it.
The magic of the hikouki kanna centers around a small spring loaded bamboo bar that pushes the kumiko flat in front of the mouth of the plane, insuring it lies flat to the planing beam. To help hold it in there it sits in a sliding dovetail cut into the dai. I’m a big fan of using wooden cut fences for starting dozuki cuts. Here’s a simple one made out of some kind of nice tropical hardwood cut for a thick veneer. There’s a lot of work where you won’t have space to use a cut fence like this, in which case a scrap piece of kumiko works great. I just give it a little lick to help it stick to the wood while I’m starting the cut, haha. Even though the cut will be angled to match the sides of the dovetail I start the kerf perpendicular with a few strokes. I also used my rip tooth dozuki, even though this is cross-grain, because the teeth are less liable to catch and break off in this oak.
With a clean straight kerf started the saw is angled to match the dovetail, same as with a jiguchi rail extension cut. I also cut down the center of the dovetail so that the waste is easier to clear out with chisel.
A nice clean sliding dovetail, ready for the spring mortise. Notice I still haven’t cut the mouth open wide enough to let a shaving pass through. I wait to do that until the blade is bedded.
As for flat spring stock, you can buy it I pretty much any size or thickness and then temper it yourself. As it is saw plate has close to the right temper for a spring. A good Japanese saw might be too hard to work without breaking from the fatigue, stick to the softer cheap plates that are closer to a purple temper, they’ll probably last longer.
I settled on a thinner spring from a disposable ryoba blade. I have no analytics as far as the required force for the spring. The drawing in Odate’s tool book shows an adjustable tension mechanism with screw adjustment. I can see how that’s useful if you’re planing a wide range of thicknesses. The simpler way is to just bend the spring until it has enough bow to give good tension. I also peened it a bit on the anvil to set the curve and stiffen it up. I used to work as a musical instrument repair technician, flutes to be specific, which use a lot of very small flat springs and wire springs (I’ve been told I have a talent for small exacting work). Seriously, you just bend it to change the tension.
I cut a mortise in the bottom of the sliding dovetail to house the spring.
Small parts require tweezers. If nothing else you gotta have a good pair on hand to pull all the splinters you get out being a woodworker. The mortise for the spring has to be deep enough that it gives it full housing when the bamboo bar is depressed. So, I can’t say how deep to make the mortise, that depends on how you bend your spring.
My bamboo bar, from pre-finished bamboo flooring. Somebody send me some fresh bamboo! This stuff sucks for making sumisashi. I planed it to fit, and then made it loose enough that about 1/16″ sticks out proud of the sole. It needs to be planed down in thickness as well, such that it can be pressed slightly below the sole of the dai.
Here’s my smoothing plane for comparison. Really the closest I could make to a copy, but with American red oak and not Japanese white oak. The next time I make a dai I’ll try hickory.
The runners on the bottom need small recesses cut to let the bamboo bar stick out. I also cut a little notch to keep the blade edge from pushing out the runners.
I tried it on a few pieces of practice kumiko and it held tolerances of four thousands of an inch, right on the money for good joinery. If I flatten my planing beam again it might do even better. This plane is also wide enough to handle two pieces of kumiko at once. It represents at least a four fold increase in the speed with which I can dimension material, awesome!