Making Kumiko
I’ve been preparing a lot of kumiko strips lately (for classes and side projects) and I thought I’d share my method for making them, since the process is a crucial step in the making of any shoji screen or kumiko pattern. Making a screen or pattern requires that all the kumiko strips be a consistent thickness, otherwise you will end up with joints that are either too loose or too tight.
Kumiko is traditionally made using Japanese hand planes to plane the strips to an even and consistent thickness. Hand planing allows for a lot of control, since it is a very gradual process, and it also leaves a shimmery smooth surface that makes for a much cleaner finished piece. A specialty plane, called a hikouki-kanna, is specifically made for planing kumiko and uses adjustable sides (or fastened wood strips) that are set to the desired kumiko thickness. The adjustable sides raise the sole of the plane off the surface of the bench by the desired kumiko thickness, so that when you are planing a strip of wood, the plane will stop planing when the sides make contact with the bench top. For more details on the hikouki-kanna check out Granite Mountain Woodcraft and Brian Holcombe’s blog posts on the subject. I haven’t made a hikouki-kanna yet, and I’m afraid to modify my existing planes, so in the meantime I’ve been using a different method for making kumiko that works quite well.
My process starts by making blanks out of which I will rip the kumiko strips. I thickness the blanks to the final depth of my kumiko. For most of my work that’s right around 1/2″, but for full size shoji screens the depth is usually around 5/8 to 3/4″. The blanks should be rift or quarter sawn, with straight even grain, so that the kumiko being ripped from the blanks will likewise have nice straight quiet grain.
After milling them to just a hair over the final thickness I’ll take a few swipes with a Japanese hand plane to give the wood a finished surface, making sure to maintain an even thickness across all the blanks.
The result is a nice clean stack of blanks, ready to be ripped into kumiko.
I rip all my kumiko on the bandsaw. I find it to be more consistent and safer than the table saw. It also wastes slightly less wood, which can make a difference when you’re ripping a lot of thin strips. I’ll take a rip off both sides of the blank, then rejoin those edges on the jointer, and then repeat the process until I use up the whole blank.
Next comes the thicknessing jig. Using a clean stable piece of wood, I’ll cut a groove down the middle, making sure that the groove is the same depth as my desired kumiko thickness (in this case about 1/8″). I usually use a router to cut the groove, because the overall result is a smoother and more consistent surface. In the past I’ve run the groove all the way down the length of the jig but more recently I’ve found it simpler to stop the groove so that there is no need to add a stop of any kind (the end of the groove simply acts as a stop). The jig loosely holds one or two pieces of kumiko at a time while planing.
I start planing the strips with a course plane to remove the bandsawn surface quickly.
Once the saw marks are gone I will switch over to a finish plane with a finer setting and nice sharp blade for a final pass. This gives the kumiko a really nice smooth finished surface.
Then I flip the pieces over and do the same to the other side, only this time I will keep planing with the finish plane until I reach the finished thickness. A couple pieces of masking tape on both sides of the plane prevents the blade from digging into the surface of the jig. The plane will stop cutting when the finished thickness is reached, and should be nearly flush with the surface of the jig.
And after going through 40 or so strips the result is a nice clean stack of kumiko. I’ve found this method to be really effective for thicknessing kumiko, as long as the groove in the thicknessing jig is cut to an accurate and consistent depth. Measuring the kumiko with a digital caliper I’ll find a little variation but not much more than a few thousandths here and there.
Thanks for reading, and hope this helps some folks out there who are enjoying kumiko work.
Nice work Jon! Appreciate the mention!
Thanks! And no problem, I’ll definitely be referencing your post when I make a hikouki kanna one of these days.
Is there a particular type of wood that you suggest using?
Sorry for the slow response,
I really like basswood for kumiko. It’s really easy to work and takes a great shine when handplaned. A lot of the work I do is with basswood.
Thanks!
Hi,
awesome stuff you do!
Congrats!
I also would like to do a lamp.
Are there any plans with dimensions available?
If I start without any dimensions, the lamp could look ugly afterwards
😉
Your detail article is amazing. Thanks so much for sharing. This helped me a lot.
Wonderful, I’m really glad to hear it helped you!
Thanks for taking the time to post up your articles!
As someone who does traditional Japanese carpentry, what is your opinion on supersurfacers , like the the Marunaka? Is it a production shop tool, or do the smaller shops use them?
It is interesting to see an entirely different approach to kumiko- in our shop, we plane kumiko slats to thickness, slot them, then run the wide slats through a gang ripsaw , then flip them 90 degrees to plane the edges to width. So the final planing controls the fit.
Thanks for reading Ed!
I think supersurfacers are great, and am currently looking for a mini model for making kumiko and planing small parts. In carpentry work we hand plane a lot of wood and a supersurfacer can really speed that process up. Some people use them here essentially as a “rough plane”, meaning they use the supersurfacer to take off mill marks and even out the surface, and then follow up with a hand plane for the final finish planing. In other situations the supersurfacer is used for the final finished surface. All that being said when the blades are sharp and with a well setup machine it’s hard to tell the difference between a surpersurfaced finish and handplaned finish.
I haven’t worked in any shops where a supersurfacer is regularly used so I can only speak to what I have heard from other carpenters, but I think the machines can easily be used in large production shops and small shops as well. There are so many ranges in terms of size and capacity that you can choose a machine necessary for different workflows. I know one of the biggest challenges to using them outside of Japan is blade sharpening. Some machines have “throwaway” blades but others have blades that need to be sharpened using specialized grinders that are hard to come by outside of Japan. Marunaka seems to be the only company still exporting machines to North America but here in Japan there are many more options and a much wider range of sizes. If you’re interested check out yahoo auctions Japan and you will find a lot of used supersurfacers at decent prices.
Your method of slotting/milling kumiko is really interesting, and sounds like it would work pretty well. The gang ripsaw sounds like a sweet machine for mass producing kumiko strips. How thick are the blades/what kind of saw kerf does each blade take?
Jon,
We made our ripsaw. It uses four 7 1/4″ diameter , 1/16″ kerf rip blades. I was using Matsushita, but I guess they are either out of business or no longer available through our saw shop, so am changing over to Tenryu blades.
The reason was both speed and safety-ripping individual strips puts a hand near the blade a lot of times. Also the chance of a really wicked kickback- the resemblance of a Port Orford cedar kumiko to an arrow is remarkable- One of employees was using a thin worn out push stick and thowing sticks- he kept wddging it between the fence and the stock I told him to get a new one. “Just one more cut”- BLAM- the “arrow” flew across the shop at me, and punched a hole right through the piece of 1/4″ mdf I had set up as a shield 10 seconds before.
Sounds like a cool machine that you’ve put together. It must speed up the process considerably. I agree that ripping thin strips on a table saw is dangerous, and have always used a bandsaw, but it’s certainly not the fastest method. It’s amazing how fast a table saw can launch a piece of wood. Someone in my old shop had kickback on a 7 1/2 hp. sliding table saw with a small piece of wood, and the piece went straight through a 1/2″ sheet of plywood.
What machine do you use to cut the notches for your kumiko? I have always wanted to conjure up a radial arm saw with some sort of sliding/indexing table. The saws in production door making shops here in Japan use that kind of machine, and I know one guy in the states that imported one but the cost is pretty steep.
Our slotter is a table saw, dado head, and cross slide table on linear guides.-along with an index pin system for spacing. We have gone through several iterations of it.
A radial saw with a Tiger Stop programmable fence and index pin would work well, I think, especially with a automatic feed on the saw head. A Putting the saw motor on a linear ways would probably be more accurate, as the rails could be supported on both ends, .
which wood good for use
When I was in the US I really liked using basswood. It’s inexpensive, really easy to work with and has a great sheen after hand planing. Here in Japan I prefer hinoki or sugi. I recommend something that is somewhat soft and easy to cut.
Best,
Jon