Heavy Duty Shelf – Design

My wife and I are entering our 5th year here in Japan, something that is truly hard to believe considering how fast that time seems to have passed. When we moved here, we each carried only what we could in a couple of suitcases. 5 years later, and we’ve now started to max out our tiny apartment with all the stuff that we’ve accumulated over that time. I will fully admit that a lot of the stuff filling out apartment are tools, wood, and furniture that I’ve built or collected. So I’m a big contributor to the problem… and my wife is a patient woman.

In any case, the discussion recently came up about whether it makes sense to try to move to a bigger more comfortable space. We quickly decided that isn’t the best option at the moment, and instead decided to just do a better job of organizing and arranging our current space to make it more liveable. One thing that we desperately need is shelving. So I’ve started to design a large heavy duty shelf for storing big items and heavy boxes full of tools, etc.

In a previous series of posts I talked about the デザイン and construction of a series of knockdown shelves. Those were designed to be more lightweight in terms of use as display shelving for artwork. But certain aspects of the design of those shelves I’d like to carry forward into this new design, namely using joinery only for the construction (or as much as possible), and designing the shelves such that they can be easily broken down for when we do inevitably move someday.

I pretty quickly landed on a simple design for these shelves, which you can see below. I’d like to build the shelves using sugi (Japanese cedar) since it’s local, relatively inexpensive and plentiful. The shelves themselves will be made up of 30 mm (~1 1/4″) thick boards of sugi. The size of the posts will depend somewhat on what size I can find at the lumber yard, but the design below shows 50mm (~2″) square posts. The last set of parts are the big x-brace on the back and a series of short stretchers that will join the legs front to back.

The main joinery considerations for this shelf are how to join the posts to the short stretchers that connect the front and back posts, and the joinery for the big x-brace that will provide racking resistance.

There are a few different options for joining the posts and short stretchers. On the Toshi-nuki shelves that I previously mentioned, these joints were glued and permanently fixed. But this time I’d like to try a knock-down joinery option. The joint I’m currently leaning towards is called a kata-sage-ari joint which translates roughly to a one-sided drop down dovetail joint. You can see a cutaway view of the joint below. The stretchers pass through the post with a one-sides dovetail cut into both stretcher and post, and the whole thing gets locked in place with a wedge. This is a joint that comes straight out of Japanese carpentry, and is one of the methods used to lock nuki to posts (nuki are horizontal cross-members which pass through the posts and provide structure for plaster walls while also helping to solidify the frame).

This joint can be blind or through, and while I really like the blind option for visual cleanliness, the ability to remove the wedges becomes pretty tricky. Whereas with the through kata-sage-ari, you can easily tap the wedge out from the outside face of the joint. So I think that’s the way I’ll proceed for this project.

For the big x-brace on the back side of the shelf, there are two areas of joinery to consider. First is simply how to join the x-brace to the posts themselves. For those joints I think I’ll notch out both the posts and x-brace at each location where they meet to create a series of half lap joints. Using half-lap joints should make the shelf incredibly rigid and provide a ton of strength to resists racking. The only issue with using half-lap joints is that I don’t want to glue the joints for future disassembly, and unglued half-lap joints don’t have anything holding them together outside of the friction of the joint itself. I may end up just using a screw or two to hold these joints together, but for the sake of a cool joinery challenge I’m also considering other options.

Which leads me to the other joinery consideration for the x-brace, the intersection of the two halves of the brace itself. Here again a half-lap joint makes sense, but the same problem remains for how to keep this joint together without glue. This is something that I’ve been pondering for a while now, and this project seems like a good opportunity to experiment a bit, so I’ve started to think about how to lock a half-lap joint together with a wooden pin.

This is what I’ve come up with.

In the front on view of the joint, it’s not clear but the pin is dovetailed shaped on both halves. Below you can see the pin removed and the mortise that runs through both parts of the half-lap joint.

Here’s a look at just one half of the joint. You can see how each half of the joint would need to be cut out to accommodate the dovetailed shape of the pin. It’s not exactly an easy joint to cut, but certainly not impossible. I think the joint could also work without adding the dovetail shape to the pin, but then the only thing holding the joint together would be the upper and bottom corners of the each half of the joint where the pin intersects. Adding the dovetail profile would add a ton of strength. It’s also subtle in the images here, but there is a slight taper to the pin top to bottom, to prevent it from falling straight through, and also to add a certain wedging action to tighten up the whole joint.

So that’s where I’m at for the moment. I really love these kinds of design and joinery challenges, and being a project that I’m going to personally use and live with gives me some extra room to play and see how things will work out over time. I’ll be sure to share the process as I get started with the build so stay tuned.