As usual, click any photo to bring up a larger version.  

Dado Strategy

 

A friend of mine recently asked me to help them design and build a rather unique project as a present for a mutual friend. This project was a wall cabinet with a whole lot (forty-five!) of individual cubbyholes.

This is not really a project that I can envision a lot of people wanting to build. But still, I thought it would be interesting to write an article that looks at the design and construction process. As you can see, this project has dozens and dozens of dados in it. At first glance, it looks like a ton of work. Even when I first drew it up, I thought it could take a lot of work. But there are a number of fairly straightforward steps that can be taken to vastly simplify the project.

There are forty-five little storage spaces in this project. There are ten horizontal pieces. Eight of them have four dados on the top and bottom, and two that just have them on one side. That works out to sixty-four dados. Then there are the two sides, each with ten dados. That gives us a grand total of Seventy-four (74) dados!!

Yet I did NOT make 74 dado cuts on my table saw. Read on, and find out how.

(ps: The project is a storage cabinet for glasses, but unless you're an optician who collects glasses I suspect it is unlikely you need a way to store 45 of them...)


Here's the design that we came up with. By working in Sketchup (a 3D drawing program) we can rapidly try different sizes, dimensions, and arrangements to come up with one that suits us.
A close-up on one of the storage cubby's gives a closer look, and also a few more of the dimensions.

Note that the shelves fit into dados in the side of the cabinet. The dividers fit into dados cut into the shelves. The back is simply inset between the two sides, no rabbets or dados there, for simplicity.

The plan was to use half-inch plywood -- Baltic birch, preferably, for the sides and shelves. The back could be from 1/8", 1/4", or 1/2" plywood. We ended up using 1/2", just for simplicity.

The dividers were to be from 1/4" hardboard (aka Masonite, or similar). The dividers were also intended to be removable -- not glued or fastened into place. This doesn't affect the construction a great deal, but it is still something to bear in mind. As mentioned previously, there are a LOT of dados in this design.

Every time you have to change a tool setting, there is a chance for error to creep in. So you always want to try and arrange your workflow such that you minimize those changes.

Take the example of cutting out a bunch of four-inch-tall drawers. Ideally you would arrange your project such that you can set the tablesaw once to make a four-inch rip, and then cut out all of the drawer pieces at the same time, so that they are all an identical width.

The same principle applies to dados. You want to minimize the number of times you change your tablesaw settings. The way to do that here, is to try cut out all the dados (or as many as possible) before you cut up the plywood into individual pieces.

In this project, symmetry is also our friend. The shelves are evenly spaced from top to to bottom, and the dividers are evenly spaced from side to side. So, for instance, I will be able to set the tablesaw to make the lowest dado on the side, but I can use that same setting to make the topmost dado by simply flipping my workpiece end-for-end.

There are only five different kinds of pieces in this project: (1) the back. (2) the sides (3) the dividers (4) the shelves and (5) the top/bottom. The dividers will be cut from hardboard, and don't have any dados, so they will not be discussed much. The back also has no dados in it, and is a simple rectangular piece. I will note that even though you know the dimensions of the back from the design, you should NOT cut it out to final size until after the rest of the project has been cut and fitted, just in case there are some minor variations that have crept into the project.

Ideally, then, we should have three pieces of plywood -- the shelves, the sides, and the top/bottom -- and then cut out all the dados in each piece at the same time. Unfortunately, it's not possible to fit all the shelves into one piece of Baltic birch (7-1/2" x 8 pieces = 60 inches, but that doesn't allow for the saw kerfs) so we'll need two sections of shelves.

In this sketch, the light blue rectangles -- positioned behind/under the other pieces -- represents a piece of Baltic Birch plywood. At 60"x60", I always need to have the lumberyard cut it into two pieces, or it will not fit into my van. So I always need to plan out a rough cutting diagram before buying my plywood.

The other pieces are then arranged on the plywood, keeping in mind grain direction. Grain direction in plywood does not matter for strength, but it does for aesthetics.

Then we plan out the cutting order. First, cut out the first block of shelves (#1 on the diagram). Here the length does not matter, so we cut it a bit long, but the width should be exact (the dimensions are noted on the drawing). Second, we cut out the block of sides (#2 in the diagram). Here, it is the opposite. The length needs to be exact, the width not so much. The width does need to be at least 1/8" wider than the sum of the two widths, to allow for the saw kerf.

Third, we cut out the 2nd block of shelves. Fourth, we cut out the top/bottom block, again being precise on width. And Fifth, we do NOT cut out the back -- just leave the piece of plywood over-sized until we are sure of the dimension.

Here is a closeup of one of the shelves, and one of the sides. The dimensions are noted here, as they are critical for the next step, which is the mass-cutting of all the dados.

Here's where the symmetry pays off...

First, take the time to set your dado set to the exact thickness you need, to match the thickness of the items that go in the dado.

Once you're ready to cut, things start to move quickly. For each cut, you can flip the board (this diagram shows the side piece) end-for-end and cut the matching dado at the other end of the board. So you get two cuts each time you set the blade.

When cutting the shelves, it pays off even more, since the shelves have dado's on both sides. So for the shelves, each time you set the saw you make four cuts before you need to move the fence.

Here is a photo of cutting the dado for the top/bottom pieces. In this case, the hardboard that I used for the dividers was only about 3/16 thick, which is thinner than I can set my dado stack. However it is still thicker than my sawblade. Fortunately I was able to find two sawblades in my collection that together made up the right thickness. So it is kind of a DIY dado blade set in that situation!

One piece of advice to remember when cutting dados in plywood is to always push down on the plywood. Otherwise you might end up with a dado that has an inconsistent depth -- plywood often can have a bit of a bow or arch to it. By pushing down, you ensure that the face of the plywood is flat on the face of the tablesaw, which guarantees a consistent depth of cut on your dado.

Here is a shot of the sides (top) and one of the shelf sections (bottom) showing most of the dados cut out.

 

And a snapshot of a test fit. At this point you can now take a measurement from the project and then cut out the piece for the back.
Time for the glue up....
I have never yet regretted buying good quality clamps.
A stack of pieces cut out for the dividers.
Time for a learning experience.

If you look carefully at this photo you'll notice that the middle shelf seems to have a larger gap than the other shelves. Don't make this mistake! When I was cutting the dado's for the sides, each time I moved the fence I measured that the gap was precisely 3-1/2", which is what I had in the design. However, I completely forgot, for the moment, that Baltic birch is sold in metric thicknesses, so it was not precisely 1/2" thick -- rather it is 12mm thick. So I ended up with a 4" gap for the middle shelf. This is no big deal, and my friend and I just laughed it off as a "custom feature".

Here is how to avoid that: I should have simply moved the fence 4" each time, instead of measuring the gap and aiming for 3-1/2". That's all there is to it. Each gap would have them been a touch over 3-1/2", since the dado is a bit less than a 1/2" wide, but they would have at least all been the same. Again, no big deal, but something worth learning.

The finished project, after a coat of shellac, followed by lacquer.
A closeup, showing two of the cubbyholes.

 

Thanks for reading!