Keyaki Tabi-dansu 2

Wedged Mortise and Tenon Joinery

Last week I covered cutting the box joints and mortises for this keyaki tabi-dansu, and this week we’re continuing on with the wedged mortise and tenon joints.

Since I laid out and cut all the mortises by hand, the location and size of each became somewhat unique. So I decided to transfer the location of the tenons for the shelves directly off of their mating mortises.

After marking the tenon locations I proceeded to mark out the tenon thickness as well.

Somewhat last minute, I also decided to cut a shallow dado in line with the tenons. The tenons on their own would be strong enough to support the shelves, but thinking really long term, adding a shallow dado combined with a mating tongue on each shelf makes for a much stronger connection, and there will be virtually no chance for the shelves to cup or warp over time.

Here are the finished dadoes in one of the cabinet side panels.

Now onto cutting the tenons. I decided to try putting the new tenon cutting table saw to use for this task. I’ve used this style of saw quite a bit at Somakosha’s shop, especially for door making, and they are amazing tools. Definitely dangerous, with the blade being so exposed, but as long as you are responsible and careful, these saws make it a breeze to cut tenons.

The shelves for the tabi-dansu just barely fit in the machine. Usually you’d use this saw to cut tenons on narrow stock, not wide panels… but if it fits, why not.

Here’s a close-up after doing a couple test cuts. With the adjustable fence you can safely sneak right up to the line.

And here are the tenons after cutting all of them to width. The only areas I couldn’t do on this machine were the cuts on the very outside edge of each board. (You can just make out the pencil lines towards each edge below.) The boards were too wide for me to have clearance to make those cuts, so I ended up cutting them with a hand saw.

The next step for the tenons was to establish their thickness with a router.

Followed by a quick test fit, to make sure the thickness was where it needed to be, and the tenons were engaging with the dadoes.

Then I set each board on end for trimming down the portion between each tenon. This is a similar setup to what I did for the box joints in the previous post. The little tongue that remains between the tenons is the portion that will engage with the dados cut earlier in the sides of the cabinet.

And here’s a look at a test fit after the tenons were finished.

With the tenons more or less done, I moved back to the mortises. The final step for the mortises was to flare them with a slight taper, such that the outside of each mortise is slightly wider than the inside. Ultimately wedges will be driven into the tenons such that they will spread into the flared mortes forming a joint that can’t pull apart.

Below is a scrap board that I used as a paring guide for flaring the mortises. I cut a very slight angle into the edge closest to the mortises to guide the chisel at a consistent angle.

I spaced the guide off the edge of each mortise using a thin 0.5mm ruler.

With the ruler removed you can see the slim amount of material I needed to pare away.

Holding the chisel tightly to the paring guide it only took a few passes to flare the mortise. From here I flipped the jig and pared the other side of each mortise as well.

Here’s another look at one of the mortise with one side pared back.

Once the mortises were done I could move on to finish planing the cabinet sides, top and bottom, and shelves in preparation for assembly. This keyak was really a dream to plane. The growth rings were pretty tight, and most of the stock was quartersawn so planing didn’t require too much muscle. But with the quartersawn stock the medullary rays were really prominent, so a tight chipbreaker was a must. Ray fleck figure can be surprisingly difficult to plane, and with too heavy a cut or a poorly set chipbreaker the grain can easily tear out.

I did a round of “rough” planing to get the surface smooth and free of any mill marks left by the planer or jointer, then I resharpened, set the chipbreaker crazy close to the edge of the main blade and took a few final light shavings.

Planing keyaki reminds me a lot of planing oak. It’s a very ring porous wood with late growth that is super hard and dense. If the wood has wide growth rings you end up having much more dense wood to plane (versus the more open porous grain), which becomes especially noticeable when planing flat sawn material. But stock with slower, denser growth rings has much more of an even balance between the dense and porous grain, which makes for a much smoother hand planing experience. The grain for the shelves of this cabinet was just starting to veer from quartersawn to flatsawn on one side, and it was noticeably more difficult to plane than the tight quartersawn grain on the side panels.

With the cabinet parts planed I started thinking about assembly, but one more bit of prep beforehand was to cut wedges for the wedged mortise and tenon joints. I’ve cut wedges a bunch of different ways, but this time decided to try something different using the tenon cutting saw. After doing a quick calculation to determine the wedge angle I needed, I set up a really quick and basic jig which has a fence set at half the desired angle. When cutting wedges it’s ideal to have the grain of the wood running straight down the middle of the wedge, so by setting the jig to half the desired angle, and cutting from both the left and right side, you end up with nice strong wedges with centered grain. Hopefully the following pictures will make the process more clear.

Below you can see the wedge stock after making the first series of cuts. I used a series of 5mm plywood shims to space the jig off the machines fence. In the picture above you can see the whole stack of spacers between the jig and fence. As I made a cut I removed a spacer, made another cut, and so on.

Then I replaced the spacers and flipped the wedge stock over to cut the opposite side.

After another series of cuts I ended up with a stick that looked like this:

Then it was over to the Pettywork saw to cut the wedges free.

And now for the real test. Each tenon is 30mm wide, so I made the wedge stock also 30 mm wide. Then I dry fit the shelves in the cabinet sides to see how the wedges would fit. In the image below you can see the tenon which has been kerfed twice with a handsaw, you can also see the 0.5mm gap above (and also below) the tenon which came from flaring the mortises earlier. I sized the angle of the wedges so that they would be a larger angle than the amount I pared into the mortise, which ensures that the tenon will compress into the flared mortise when the wedges are pounded in. It’s amazing how much wood can compress, even hard dense wood, so I’ve found it beneficial to go a little heavy on the wedge angle.

Here’s a test fit of the wedges to ensure the width was correct. The wedge stock is white oak.

And here is one side of the cabinet with wedges ready for some glue.

The glue-up itself was pretty straightforward. I used a few cauls and clamps to make sure the shelves were snug up to the sides of the cabinet…

… then put a bit of glue on each wedge and pounded them home.

The clamps really helped to make sure the shoulders of the shelves closed up nice and tight to the cabinet sides.

And here’s the cabinet with wedges fully glued and tapped in.

Well that’s all for this week. This post was a long one. Lots of pics and scattered bits of info, but hopefully interesting for you. There’s lots more I could say about wedged mortise and tenon joints. They’re simple joints but definitely have their challenging spots. If there’s enough interest it might be work doing a deep dive one of these days.

Back next week with more on this cabinet build.

Thanks for reading.