# The Dado Hewn Shop Notes ยท https://hewn.build/shop-notes/the-dado-75 AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it. Cite as: "The Dado." Hewn Shop Notes, hewn.build/shop-notes/the-dado-75. Drafted 2026-04-22; AI-drafted, not yet checked. --- The dovetail gets the mythology. The dado does the work. Every bookcase shelf that isn't sagging sits in one. Every drawer bottom that doesn't rattle floats in a groove. Every frame-and-panel door that survived ten seasons without splitting has a channel holding the panel loose enough to move and tight enough to stay put. The dado and its cousin the groove are the quietest joints in the shop, and probably the most load-bearing ones you'll cut this year. Quick distinction, because it matters structurally. A dado runs across the grain. A groove runs with it. Same cut, different name, different consequence. A groove runs parallel to wood movement, so you can make it tight. A dado crosses the grain, which means the mating piece will move in the channel. Your fit has to account for that or you'll crack something. ## Where they earn their keep A shelf screwed to the face of a bookcase side has zero mechanical resistance to racking. Push the top sideways and the whole case parallelograms. A shelf seated in a dado resists that. The channel locks the geometry. That's not a nice-to-have. That's the joint doing its actual job. In a drawer, the bottom floats in grooves plowed in the sides and front. Loose enough for seasonal movement, tight enough that it doesn't rattle when you close it. In a frame-and-panel door, the panel floats in a groove sized so it can expand without blowing apart the frame. These are all the same idea: a channel that holds something without trapping it. ## The one-third rule Cut the dado to one-third of the stock thickness. Not one-quarter. Not half. Here's why. Bending stiffness scales with the cube of height. When you cut a dado at one-third depth, you're removing material from the outer layer of the remaining cross-section. Go deeper, say to half, and you've cut into a zone that contributes disproportionately to stiffness. The shelf sag gets ugly fast. A quarter-inch dado in three-quarter stock is already at the limit. A quarter-inch dado in half-inch stock changes the physics entirely. Be conservative on spans over 30 inches or stock under 3/4". ## Width and fit Size the dado slightly undersize, then bring it to exact fit with a router plane. Don't size the shelf to the dado. Size the dado first. The fit standard: registers by hand pressure. A shelf that rattles will let the case rack under load. A shelf that needs a mallet will fight seasonal movement until something cracks. And measure from the actual shelf board, not from the plans. Lay it across the case side and mark directly from the piece. Nominal dimensions lie. The board in your hand doesn't. ## Cutting by hand Score both walls with a marking gauge or knife against a reliable square. Go deep. You'll be paring to those lines. Rough out the waste with a wide chisel, working across the channel in light horizontal passes. You're not going to depth here. You're clearing room so the router plane can work. Set the router plane to final depth and take long passes end to end, cutting with the grain. Light cuts. The plane should be cutting, not dragging. Check depth at multiple points along the channel. A bowed workpiece will give you a good floor at both ends and a hump in the middle. The shelf will rock on that hump, and you'll see it in the case front. ## Stop before the face On anything that's going to be seen, stop the dado before it reaches the front edge. A through-dado on an otherwise clean bookcase side says you ran out of patience at the end. Mark the stop. Plunge a chisel straight down at the line to create a clean wall. Rout the channel to within an inch of the stop, then pare to the wall. The mating shelf gets a small notch at its front corner to clear the stopped end. This takes five extra minutes. It's worth every one of them.