The majority of slots cut in wood are used for assembly purposes. Other applications include crafts, to provide relief for nuts and bolts, ventilation -- and anything else you can dream up. Sometimes referred to as dado or dado slots, depending on type or orientation, they are typically cut with a table saw or router. It's one of the first things novice woodworkers and cabinetmakers should learn. Groove and slot cutting is basic, a technique you can learn with a little practice.
Dado Blade Install
A dado set installs in the saw just like an ordinary blade, but turn off the power or unplug the saw before you work on it. Dado blades consist of four or more blades stacked together to create the width needed for the slot. Two blades typically make a 1/4-inch-wide slot. Four blades create a 1/2-inch slot. Each additional blade makes the slot 1/8 inch wider. When the width is correct, place the nut on the shaft and tighten it with a wrench to secure the blades together. Another type of dado blade is a single, adjustable blade that sways from side to side. It's tricky to use. Stick with the stacking blade for the best results.
Throat Plate Install
The original throat plate -- the oval-shaped insert -- that comes with your saw will not accommodate a dado set; it's too narrow. Make one out of 1/2-inch plywood, or purchase a dado throat plate when you buy the dado set. Sometimes referred to as zero-clearance, the custom insert prevents slots from chipping and splintering. It drops into the recess where the original throat plate you removed goes.
Measure Slot Location
Set the location for the slot in the wood, in relation to the table saw fence. The process is the same as if you were using the saw to cut wood normally. When you've established the measurement for the fence, lock it down and use the tape to measure the vertical height of the blade to set the depth of the slot. Crank the blade up or down, as needed, to get it right.
Cut the Slot
Turn the power on for the saw. Keep your hands well behind the blade, and run a test board over the blade. Use one hand to hold the board against the fence with downward pressure. Feed the board over the blade with the other hand. Make short passes, keeping firm pressure on the board at all times. When you come to the end of the board, use a push-stick to finish pushing the board at least 6 inches past the blade before you turn off the saw.
Router Slots and Bit
Use a standard flute-bit without a bearing to cut slots. The width of the slot is determined by the width of the bit. Install it in the router, and set the height of the bit as needed for the depth of the slot.
The setup consists of a guide board or template that's used to guide the router in a straight line. Almost any scrap board will suffice as a guide. Clamp the guide to the table, with clamps at both ends. Move the clamps when needed to access the full length of the board.
Cut the Slot
Pull the router along the guide board, keeping firm downward pressure on the router. Don't force it -- allow the bit to cut at its own pace, smooth and evenly. Deeper, wider slots sometimes require several passes. Start shallow; make the first pass, and deepen the slot as needed by adjusting the bit with each new pass.
The plunge feature may be used, if desired, particularly for slots that do not terminate on the edge of a board. It also allows the router to cut a slot all the way through the wood. Router tables also cut slots. The router is clamped upside down to the underside of the table. The bit extends upward to cut the slot on the bottom of the board.