Dados
Sometimes words are related in ways that are not apparent at first glance. Dada was an art movement and the dado joint is about wood movement. So there.
A dado is a wood joint composed of a tall piece, an inserted piece, and a cross grained groove. The tall piece, like the side of a shelf, has grooves cut across the grain at a depth of 1/3 to 1/2 of its total thickness. This groove is exactly the width of the thickness of the inserted piece.
Dado joints are often used where shear strength is important, as in bookshelves. A glue joint with end grain and side grain would be very weak. Using attachment devices like nails or dowels could cause either piece to crack due to uneven movement. In addition, the shear strength would be limited to the attachment devices.
With a dado joint, the shear strength is derived from end grain wood, which is one of its strongest points.
Stanley understood the importance of dados and made several planes for that very purpose. The first was the #46, Trauts combination dado plane. That was followed up with the #39 set. This set of eight dedicated planes is graduated from 1/4 to a full inch.
Of course, these tools need a helper. That is where the stair saw comes in. Here are two examples.
The top one is a recent Ulmia from the 1990s. The lower one is a very early Disston. It was damaged in a fire and I remade the front horn. In fact, I customized it to fit my hand. My saw, my rules. But here is where the Sesame Street song comes in. "One of these things is not like the other." Can you tell the difference? Here is another clue.
The early one is made for cutting dados and the Ulmia is made for cutting sliding dovetails. What is a sliding dovetail, you ask? Tune in for tomorrow's lesson. Today we are talking about dados.
The first step is to place the inserted piece on the tall piece and scribe a line on each side. Then you push your stair saw along that line to make a kerf. Stair saws cut on the push stroke. Here it is in action.
The stair saw blade adjusts to the depth of your dado and ceases cutting when that depth is reached. It is easier to control than a larger saw. Look at this large 12 pointer. It would cut the dado but would be very hard to control the depth.
After a little sawing, the dado kerfs are made.
The proper #39 plane would be the 7/8. BUT that is still in as found condition. Yet another project. Lucky for me that the next one down, the 3/4, is ready to go and has one of my custom blades. Cutting the dado waste can also be done with a chisel, but the #39 plane is quicker and easier. It leaves shavings that look like the stuff you find in pencil sharpeners. That is because cutting cross grain is difficult unless the blade is skewed. And the skewed blade leaves a funny looking shaving. But it looks nice when cleaned up.
The true test is fit. And in this case--perfection. The insertion piece fits snug into the slot.
So there is the dado joint. Sometimes these joints are glued and sometimes they are spiked with nails. If the fit is snug and the case is tight, I limit the spike to a single nail in the center. That strategy allows wood movement on both sides with a very low chance of splitting.
Dados can be made using routers, tablesaws or just chisels. I encourage you to use a dado in your next project. This strong joint will reward your attention with years of strong service. Time to go make some shavings.
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or maybe it's the piece under it that doesn't. I have that wood right now. That's my brothers project to hold his hole saws. He's 10. My dad will probably use 1 file a year would pine atleast work for that?
what kind of wood is this or maybe it's the piece under it that doesn't. I have that wood right now. That's my brothers project to hold his hole saws. He's 10. My dad will probably use 1 file a year would pine atleast work for that?
