Find out all about dado joint, what makes it different from other joints, how it is made, the three types of dado joint, and how to use them effectively.
Wood joinery methods are more or less based on a similar concept to one another. This woodworking concept involves adhering two members at either a parallel or perpendicular angle, either by using extraneous mechanical support, or by designing clever slots and inserts to reinforce a woodworking joint. It is easy to mistake one type of woodworking joint for another, but you’ll find if you pay close attention, you’ll understand why there are so many subcategories of wood joints.
The dado is a joint that can easily be mistaken for another type of wood joint. However, dado joints are rather unique in their straightforward functioning mechanism.
What is a Dado Joint?
The dado joint is a simple joint that every woodworker should feel at ease using, as it is a basic element in almost any woodworking practice. In the UK, a dado joint is referred to as “housing,” and in Europe, it’s referred to as a “trench.” Both these names are indicative of the dado joint’s shape.
A dado is a three-sided channel that is carved against the grain of a wood workpiece. It’s important to note that a dado is cut against the woodgrain, because if the dado was cut along with the grain it would be called a groove. Grooves should be placed in a specific area different from channels. But instead, the dado itself is the channel, which also labels it automatically as a dado joint. A rabbet is the workpiece inserted into the dado channel, which then becomes a dado joint.
The dado channel should have clean-cut shoulders (which are the walls leading from the floor of the slot to the surface of the workpiece) and a perfectly flat bottom. A correspondingly-sized wood workpiece will then be inserted into this slot. This workpiece is usually called a rabbet.
The dado channel itself should be cut no more than half the width of the workpiece, as any wider cut threatens to weaken the overall structural integrity of the wood workpiece. The recommended measurement of the dado channel is one-third of the overall workpiece width.
The dado joint is almost always reinforced with glue. Once a piece that uses dado joints is loaded with books, or a rock collection, or dishware, the weight of the load is transferred directly to the sides of the structure, which is then by proxy transferred to the floor.
Dado Joints Can Be Used…
Since the dado joint isn’t significantly sturdy, it isn’t normally used in larger construction projects. It is, however, sturdy enough to handle whatever can be found on a standard size bookshelf, so that is the place where dado joints are most often used and found.
Typically, the dado is placed along the front face of a workpiece. The dado joint can be found occurring multiple times on a piece with multiple shelves. The dado is not a joint that is used on the edge of a workpiece, and simply gluing a dado joint at that corner edge will create a dangerously weak wood joint. A dado joint needs a top shoulder and a bottom shoulder to be supported and to bear weight.
Dado joints are excellent for wherever long and thin wood pieces are being used. The workpieces shouldn’t be too long, though, since lighter wood is more often used with dado joints. Long, thin wood is incredibly vulnerable to bending in the center when bearing excessive weight.
Three Types of Dado Joints
The Through Dado: this occurs when the dado channel is cut from end to end of your workpiece, leaving both ends open (this technically becomes a mortise and tenon joint, only longer).
The Stopped/Blind Dado: this occurs when the dado channel stops just short of the edge of a workpiece. The stopped/blind dado is used when a craftsman does not wish for the joint to be seen from the front. This type of dado joint usually ends up being one of the stronger types of dado joint, as an extra notch must be cut into the attaching piece to create a slight overlap, also creating significant extra reinforcement.
The Half Dado: this is where the rabbet comes into play. The dado channel is cut in the same way as the other types of dado, but instead of having only one flush edge to insert into the dado channel, the corresponding member has an extra little shelf (or step), with the top step inserted into the channel. This typically looks like two upside-down wood steps. This type of dado joint can be a great solution to help camouflage any imperfections in either workpiece.
How Does the Dado Compare to Other Joints?
The dado joint is one of the weaker types of woodworking joints, as it relies heavily on glue and even extra nails to be at its sturdiest. But, due to the dado joint’s simple and cheap manufacturing process, it’s what is most often used in building cabinetry and shelving. But don’t worry; the dado joint is strong enough to support the items that are usually found in cabinets and on shelves.
The dado joint is most similar to the mortise and tenon joint, but it tends to be quite a bit longer than the mortise and tenon. The mortise and tenon joint is almost always joined at the ends of members, as well, unlike the dado.
The dado joint is often mistaken for the butt joint. These two joints are rather similar in function, but there is one element that makes the dado sturdier than the butt joint. The butt joint is most often just joined at two sides, so there is less surface area to glue than there is on a dado joint. The dado joint is technically composed of six glued sides, as the dado cut channel has three sides and the inserted workpiece has three sides joining those. Since this joint is housing, there is more opportunity for reinforcement, usually accomplished using glue and/or nails.
How deep should a dado joint be?
The most common depth of a dado channel is one-third the width of the entire workpiece. Any wider, and it may weaken the structural integrity of the workpiece.
How do I cut a dado joint?
There are several sources on how to create a dado joint. Here is a reliable one, explaining the methods with a circular table saw or a router —> The Spruce.
What is the difference between a dado and a rabbet?
There’s a full article on the rabbet here but simply put, the rabbet has an extra notch carved into its edge as extra reinforcement. It looks like two stair steps flipped upside down, with the top step inserted into the dado channel.
What is a blind dado?
This is a dado used when the craftsman does not want the joint to be visible. This dado channel stops just short of the edge of the workpiece, covering the joint location.