A dado is as a rectangular channel cut into one board to receive the end of another. Woodworkers use different methods to achieve this type of cut, but a common choice is using a dado blade. The dado blade attaches to a table saw to cut a groove in the material to the depth and width required for the joint.
For a successful dado joint, it is important that the size of the channel be such that the material sits tightly within it. Sides of the dado joint are called the shoulders. The best joints have straight and even shoulders and a flat bottom.
While the dado is a joint itself, the blade can also create other types of joints. Lap joints and butt joints are simple variations for which a dado blade can be used. With a bit more skill and patience, more complex joints – such as mortise and tenon, and box joints – can be created as well.
One type of dado blade is a wobble style blade. The blade teeth cut from side to side in a wobbling motion to the width determined by a dial setting. While this kind of dado blade usually is less expensive, it can present challenges to making a clean dado cut on less substantial table saws. Due to the nature of its cut, it usually leaves the bottom of the dado slightly concave rather than flat, which is preferred.
Another common style used is a chipper or stacked dado blade. In this type, multiple blades along with chipper blades are placed together with shims or spacers in between each blade. Adding and removing the number of chipper blades adjusts the width of a dado cut. Cuts made with this style of dado blade usually leave the bottom more flat than wobble style blades do.
Most dado saw blades require an initial setup and adjustment. The width and depth of the dado needed is calculated and the blades configured appropriately. Many different manufacturers offer styles of dado blades, and the fine-tuning of the blades can vary between different table saws.
Woodworkers sometimes use a router to create a dado cut. Specialty bits, such as a plywood router bit, insert into the router to cut a predetermined dado. These types of cuts tend to come in specific sizes and are less flexible with the width adjustment of the dado.
Of course, there were dado cuts before there were power tools. In this method, the shoulders of a dado can be defined by a backsaw, sometimes called a tenon saw, and then a chisel removes the material from the channel. Usually, a good amount of expertise is required for using this method to make consistently accurate dado cuts.