Dado joints are one of the basic joints used in woodworking. In the cabinet and furniture end of woodworking this joint is used to hold stationary shelves, cabinet backs, drawer parts and several other applications. They're easy to cut using a table saw, router, hand planes, or chisels. Also there are several variations of the dado, used to accomplish different objectives.
The blind dado effectively hides the actual joint and makes the piece look like it's just butted together. This is a much cleaner look while still giving the joint the extra strength of a inset dado.
Besides glue, most blind dados are reinforced with some kind of mechanical fastener such as nails or screws. When nails or screws aren't an option then the standard joint can be modified so nails or screws wouldn't be needed.
The sliding dovetail, another variation of the dado joint, can be used to strengthen a joint when nails and screws would detract from the look of your project. It can also be modified to be a" blind" joint for a cleaner look.
Here's a few things to keep in mind when working with dados. If your project requires that you cut a dado across the grain in either wood, plywood or especially melamine board, be extra careful to prevent tearout along the edges of the joint.
One of the best ways to prevent tearout is to score the edges of the joint with a sharp knife before cutting. Scoring several passes with a light touch will give you the best results. (This doesn't work very well with melamine. Other methods work better for melamine which I'll point out later.)
If you're using a table saw you can try scoring the surface first by having your dado blade barely high enough to cut the surface of the board. After that just raise the blade to the height that you want to cut the joint and run your board through again.
You can also increase your chances of a clean joint by using a Triple Chip Grind or Alternating Top Bevel saw blade. These blades work much better in cross grain than Flat Top or Straight saw blades.
Using a router usually requires that you use a undersize bit and 2 passes to get the right width of cut. Plywood is seldom full thickness so you normally have to make 2 cuts to get the dado width and the plywood width to match properly.
A straight groove cutting router bit normally works best. You can also get good results with a helical down cutting bit. You probably should stay away from helical up cutting bits in most materials.
Now, back to Melamine. Because the surface of melamine is so hard and brittle the absolute best way to make any cut is with a router. (Just my opinion.) CNC or hand held.
The best way, if you're using a table saw, is to use the scoring step. To finish off a cut in melamine I like to lightly sand the edges of the cut.
If your project requires a flat bottom in your dado joint then the best blade to use would be a stacking dado set such as the Freud Pro Dado Set. The adjustable type dado blades will leave a slight curve at the bottom of the joint.
If you want to just use hand tools, develop your own techniques with the tools you have and remember that patience and light touches will always give you the best joints.