Making Shoji – Western Red Cedar

A couple weeks ago I finished up a set of shoji screens for a customer in the US. I had planned to use sugi (Japanese red cedar) for the screens but ran into some issues sourcing suitable material. The biggest issue that arose was price. Wood prices lately are crazy. I think Japan has been spared the extremes that woodworkers have had to deal with in the US (I’m not sure how the rest of the world has faired), but little by little prices here in Japan also keep creeping up and up. So when I started sourcing clear, knot free, sugi, the price seemed to be almost double what I was expecting.

That led me on a search for alternatives, and after a fair amount of searching and consideration, I came across some western red cedar at a local lumber dealer. It seemed completely wrong to me to buy material that was imported from N. America to Japan, only to ship it back to N. America, but in this situation there weren’t many other options. Taking all factors into account, and with the clients approval, I bit the bullet and bought some of the last few pieces of western red available.

I started by milling up all the parts to rough size on the band saw, then joined and planed all the parts to width and thickness, leaving them long for cutting to length later. Below you can see the stack of kumiko that will make up the horizontal cross pieces of the screen. When ripping kumiko out of a larger board, I like to keep track of each piece as it is ripped, so that I can arrange them in the screen the same way. That way the kumiko will have a consistent grain pattern and direction when installed in the screen, making the overall result feel more uniform. It’s important to label the pieces ASAP, because after milling and handling stacks of material, in no time things tend to get out of order as you can see in the photo below.

Next up I laid out the mortises for joining the rails and stiles. I like using double tenons, and it seems to be the standard among furniture and door makers here in Japan. Double tenons offer twice as much surface area for gluing making them really solid. Double tenons may seem more complicated than a single tenon, but it’s definitely not double the amount of work. Particularly when you work evenly off each side of the joint, allowing layout and cutting to be done by flipping the work front to back and using the same tool settings. The shoji stiles pictured below are 30 mm thick, with 6 mm tenons. That means I could use two marking gauges set at 6mm and another at 12mm and work off of each face of the stile to layout the spacing of the mortises below.

Here are the mortises laid out for the kumiko. The kumiko are 10 mm thick by 18mm deep. I laid the mortises out for 9 mm square mortises, but the actual mortise bit is 9.5mm I believe. That way there is a bit of compression when fitting the tenons, which helps to ensure a clean look on the sides of the kumiko where there is no shoulder.

Here are the double tenons after mortising. The mortiser bit is actually 6.4 mm, a bit wider than my 6mm layout lines. Rather than layout for a really fiddly size like 6.4 mm, I find it easier to layout out with an even 6mm spacing and then when mortising stick to either the inside or outside lines as my baseline for the mortiser bit.

With the mortises cut, I moved onto cutting the tenons, which was a pretty straightforward task. I first cut the shoulders on the sliding table saw and then cut the tenon cheeks. A few people have asked me why not use a bandsaw for cutting tenons vs the Japanese tenon cutting saw. A well setup bandsaw can cut pretty clean tenons. But my problem with bandsaws for tenons is that, once the blade starts to get a bit dull, it likes to wander and follow the grain particularly on softwoods with big differences in density between the summer and winter grain. The tenon saw, with standard table saw blade, doesn’t move much, even when it’s not in tip top shape. But another issue pops up when cutting double tenons. A bandsaw can’t easily clear the waste between the two tenons, whereas a circular saw blade can knock out the waste with ease eliminating any need for tedious chisel work.

The final cutting was the half-lap joints and tenons for the kumiko. This time I cut all the kumiko on the sliding table saw, using some stop blocks and mag-blocks to securely hold stacks of kumiko. I worked in three batches. There were 7 horizontal kumiko per screen, but I cut three extra pieces to have as a backup (you never know), hence the last group is bigger.

After cutting the kumiko to length, I then cut the shoulders of the tenons using a stop block on the tablesaw’s fence; flipping the kumiko end to end and top to bottom. From there I laid out the half-laps on one kumiko and used it to set the stop blocks to cut the half-lap joints. I cut the half-laps on the tight side, a little over 0.5mm tight, to allow room for planing. I find planing after cutting these joints to be safer than cutting them before. I’ve done it both ways, and what I find is that if you plane all the pieces first, all of the little inconsistencies that come from hand planing add up when you stack the kumiko together. Then when you clamp all those pieces tight to cut the joinery there’s a certain amount of slop that tends to lead to inconsistencies between the length and squareness of the cuts.

Imagine a stack of 10 kumiko after milling with a planer. If you took a caliper and measured that stack at various points the measurements should all more or less be the same. Now if you hand plane all the kumiko in that stack and measured again, I bet there will be a lot of inconsistency. It’d be one thing if you could take perfectly even shavings, or were using a super surfacer to finish plane, but when doing it by hand, it’s nearly impossible to get consistent shavings on every single piece. Particularly when you have tricky grain that tears out, requiring more passes.

So after experiencing those challenges first hand, I’ve started to cut kumiko joinery before planing, keeping the fit of the half-laps joints tight.

The other side of this discussion is that with the joints cut, you now have a limited amount that you can plane the kumiko before the joints become loose. The whole situation is a double edged sword. This time around I had some tricky grain to plane, which is no surprise for western red cedar. I aimed for the best surface I could get, but had to draw the line after 3 or 4 passes, even if I felt like I could do better. (That’s the constant challenge inherent to hand planing.)

Here are the completed kumiko, hand planed and with joinery cut.

After the kumiko, I hand planed the rails and stiles, ending up with a nice clean stack of parts ready for assembly.

I started assembly with the kumiko grids. Some of the half-lap joints were still a bit tight, but after a light bit of 木殺し, ki-goroshi (tapping the sides of the joint with a hammer to compress the grain), things fit together really well.

Next, I glued and clamped on the rails and stiles, essentially completing assembly of the shoji. All-in-all things went pretty smoothly, and compared to the first shoji screens I made several years back, my stress level during glue-up has gone down considerably. In the past I think I always erred on the side of caution and made my joinery too tight. Sometimes you can get away with that, but when it comes to shoji, if all of the kumiko are a bit too snug, then all those little tenons together really start to fight you as you try to attach the rails and stiles. You end up having to pound things together or add excessive clamping force which can potentially split the thin kumiko strips.

Here’s a peek at one of the details that is really common on doors nowadays here in Japan. These adjustable rollers are great. They allow easy adjustment of the door for aligning it with the surrounding frame, and allow the whole door to slide nice and smoothly. Traditional shoji slide in wooden tracks, with the bottom of the door sliding against the wooden track. Traditional doors like that can glide beautifully, but if you aren’t careful to regularly clean grit and dust that falls into the track, pretty soon both the track and the door start to wear considerably. So the modern method of avoiding that wear is to use wheels like these. There are different wheel profiles for running on metal rails, but these particular wheels are flat for use in a standard shoji track. Since tracks are usually made of soft wood, we often glue in a hardwood like cherry into the track to provide a more hard-wearing surface.

And here are the finished screens with paper installed. There’s really nothing like the look of shoji. As a room partition or window covering they really change the look and feel of a space.

This past week I started work on a couple new furniture projects so stay tuned for a post on that work next week. Thanks for reading.