Grooves in wood can be used for a multitude of applications. Also known as "dados," grooves are cut into wood to facilitate the building of cabinets and furniture or anywhere two pieces of wood need to be joined. Grooves can be almost any width or depth and are accomplished with a special set of adjustable saw blades. The woodworker adjusts the width of the groove with the blades, and the depth with the saw.
Turn off the power source to the table saw. Remove the throat plate and the blade from the table saw. Open the dado set and remove the two big blades and two small blades.
Place one big blade on the table saw followed by two small blades and then the other big blade. Tighten them all securely.
Raise the blade to 1/2 inch from the tip of the highest tooth to the point where the blades emerge from the table saw.
Set the table saw fence at 12 inches from the blade to the fence. Place the scrap plywood board behind the blade, against the fence.
Turn the power source to the saw back on. Turn on the saw. Hold the plywood with both hands on either side. Push gently on the board until it passes over the blade. Hang on tight and in one smooth movement push the plywood across the top of the saw over the blade until the blade emerges out the back of the plywood.
Let go of the plywood when it is safely past the blade. Turn off the saw.
The instructions here are for an example. You can cut thinner, wider, deeper or more shallow grooves in wood by adding and subtracting blades, adding or subtracting height from the saw blade.
Always wear safety glasses and be aware of possible kickback which increases when using multiple blades on a table saw.