A dado is a slot, cut into a board, for the connection of another board at right angles. It is a very common woodworking joinery technique for joining pieces together. If you look at a quality carcase (the wood cabinet for a chest of drawers, without the drawers) you will see that the horizontal pieces of wood go into slots cut into the vertical pieces. You might also find this on a bookshelf. This cut, which must be the exact width of the board’s thickness, is the dado.
Dado blades are specialty blades, designed for cutting this slot. Generally speaking, there are two basic styles of dado blades: stacked or wobble. The stacked blade appears like a series of circular saw blades, which are stacked together on the arbor, to match the thickness needed. The teeth of the blades will overlap the cuts of the adjacent blades on either side, creating a smooth bottomed dado. These blade sets consist of side blades, which appear as regular combination blades and a set of “chippers” to go between them. The side blades are more critical, as they must make a clean cut, while the chippers are only removing the material between the side cuts. Never mix up the blade set, using a chipper as a side blade.
Wobble blades are considerably cheaper, harder to work with, create a lot of vibration and don’t produce as neat a dado cut. The blade is mounted at an angle on a two piece bushing. Turning the bushing increases or decreases the angle of the blade, increasing or decreasing the width of the dado cut made. A good cut can still be made with a wobble dado blade, by first cutting either side of the dado slot with a standard crosscut or combination blade. The dado blade can then be used to cut out the material between the side cuts. Final cleanup of the bottom of the cut can be made with a chisel and mallet.
Although some woodworkers try and use dado blades on table saws, they work best on radial arm saws. These cuts are almost always crosscuts, which are hard to complete accurately on table saws. Never try and use a dado blade on a hand-held circular saw as it would be impossible to control properly. Both types of dado blades are typically smaller than the normal rip and crosscut blades used on power saws. However, this isn’t a problem, as table and radial arm saws can accept smaller blades without problem. On table saws, you will have to change the throat plate on a table saw and probably remove the blade guard on a radial arm saw. Use extreme caution, as your blade guard will not be in place.