Cutting an accurate dado requires careful setup and execution. Here’s the manual process:

1. Determine Dado Dimensions: The width of the dado should match the thickness of the shelf or panel it will house. The depth is typically one-third to one-half the thickness of the board you are cutting into.
2. Measure Your Materials: Never assume a 3/4" plywood is exactly 0.75" thick. Use calipers to measure the actual thickness of the mating piece to determine your target dado width.
3. Set the Blade Depth: Adjust the height of your table saw blade or router bit to the desired dado depth. A 1/4" depth is a common starting point for 3/4" material.
4. Set Up Your Fence: Position your table saw fence or router guide to mark the location of the first cut.
5. Make Multiple Passes: If using a standard saw blade, make the first pass. Then, move the fence away from the blade by slightly less than the blade's kerf and make a second pass. Continue this "nibbling" process until you reach the desired width. Test the fit with your shelf material as you go.

• Dado: A square-shouldered channel or groove cut across the grain of a board.
• Rabbet: A similar groove cut along the edge of a board, having only one shoulder.
• Groove: A channel cut *with* the grain of a board. While functionally similar, a dado is technically cut across the grain.
• Dado Stack: A specialized set of stacked saw blades used on a table saw to remove a wide swath of material in a single pass, creating a dado of a specific width.
• Kerf: The width of the material removed by the saw blade. A standard blade is 1/8" (0.125"), while a thin kerf blade is narrower.

"The perfect dado fit is a 'slip fit'—it should be snug enough to hold the shelf, but not so tight that you have to force it in with a mallet. A friction fit can actually cause the surrounding wood to bulge or even crack. My trick is to aim for a fit where the shelf will slide in under its own weight, but with a slight bit of resistance. When you're making multiple passes, always test the fit on a scrap piece of the same material before cutting your final workpiece. It's a five-minute check that can save a $50 panel." - Professional Cabinetmaker

Bookshelf Construction: You are building a bookshelf from 3/4" plywood and the shelves are also 3/4" plywood. Your goal is to cut dados into the vertical sides to support the shelves.
The calculator will recommend a dado depth of about 1/4" to 3/8" for optimal strength. If you are using a standard 1/8" blade, it would calculate that you need 6 passes to create a 3/4" wide dado. (`0.75 / 0.125 = 6`).

Drawer Box with Inset Bottom: You need to cut a 1/4" wide groove in 1/2" thick drawer sides to hold a 1/4" plywood bottom.
The calculator would suggest a depth of about 1/4", as the bottom doesn't need to be deeply set. It would confirm that two passes with a 1/8" blade would create a perfect 1/4" dado.

• Assuming Plywood Thickness: "Undersized" plywood is common. A board sold as 3/4" might actually be 23/32" thick. Cutting a 3/4" dado will result in a sloppy fit. Always measure.
• Cutting Too Deep: A dado that is more than half the thickness of the board can severely weaken the structural integrity of the piece.
• Inconsistent Passes: When making multiple passes, if the board is not held firmly against the fence for every cut, the resulting dado will have uneven walls.
• Using a Dull Blade: A dull blade or dado stack will cause tear-out and leave a rough, uneven bottom surface in the dado.

• Bookshelves: The most common application, providing strong, stable support for shelves.
• Cabinet Carcasses: Joining the sides, top, bottom, and back panels of a cabinet box.
• Drawer Construction: Cutting grooves for drawer bottoms.
• Frame and Panel Construction: Cutting grooves on the inside of stiles and rails to hold a floating panel.