How to Cut Perfect Dados with a Router or Table Saw
A dado is a rectangular groove cut across the grain of a board. It’s the joint of choice for fixed shelves in bookcases and cabinets – stronger than a screw through the side panel, cleaner than a bracket, and self-aligning during assembly. Getting dados right means cutting them exactly the right width (so the shelf slides in snugly without gaps but comes apart for dry fitting), exactly the right depth (no more than one-third the board thickness), and exactly square across the panel. This guide covers both the router method and the table saw method, with setup procedures for each.
Router Method with a Dado Jig
The router dado jig is a shop-made guide that clamps across the workpiece and guides the router base along a straight line. The guide is a straight piece of MDF or hardwood at least as long as the panel is wide, with a fence on the underside that positions it at the correct distance from the dado layout line. The offset between the jig fence and the router bit is fixed – you set the jig once, and every dado cut is positioned by the same offset, making perfectly spaced dados repeatable without recalculating each time.
Setting Up the Router for Dados
Use a straight bit or a spiral upcut bit with the same diameter as your target dado width – or slightly narrower, making multiple passes. A 3/4-inch spiral upcut bit in a single pass produces a clean-walled dado in plywood. Set the bit depth to one-third the panel thickness – for 3/4-inch plywood, set 1/4-inch depth. Adjust the jig fence for the bit diameter and test cut in scrap. The shelf should slide in with firm hand pressure. If it’s loose, the bit is larger than labeled; if it won’t fit, the dado is narrow and needs a second cleanup pass.
Table Saw Method with a Dado Stack
A dado stack is a set of stacked saw blades that cut a wide flat-bottomed groove in one pass. Most dado sets adjust from 1/4 inch to 13/16 inch by combining an outer blade, chippers in the middle, and shim washers for fine adjustment. Set the stack width to match your shelf thickness exactly – measure the actual thickness of the shelf material with calipers, not the nominal size. Height is set the same as with the router: one-third of panel thickness.
Running the Cut
For the table saw dado, the panel rides flat on the table with its face up, guided by the miter gauge. A sacrificial fence board clamped to the miter gauge at 90 degrees to the blade gives a wide, stable backing surface that prevents tearout at the back edge of the cut. Mark your dado positions on both edges of the panel, align the layout marks with the outer edges of the dado stack, and feed the panel steadily. Don’t stop in the middle of the cut – a hesitation leaves a visible ridge in the dado bottom.
Pro Tips
- Cut dados in all panels for a given project before cutting any other joinery. Getting all the dados right first means any tearout or test cuts don’t appear on finished surfaces.
- Label each shelf panel and its mating dado during dry fit. Dados that fit one shelf perfectly may be slightly tighter or looser on a different piece due to thickness variation in the sheet goods.
- For stopped dados (that don’t run to the front edge of the panel), use the router method – the table saw can’t stop a dado accurately. Mark the stopped end on the workpiece and the router table or jig, and stop the router when the bit reaches the mark.
FAQ
What’s the right depth for a dado?
One-third the panel thickness is the standard. For 3/4-inch material, that’s 1/4 inch. Deeper dados weaken the panel; shallower ones don’t provide enough support for the shelf under load.
How do I fix a dado that’s too wide?
Glue a thin strip of wood into the dado to reduce the width, then re-cut to the correct width after the glue cures. Or laminate a thin strip to the edge of the shelf panel to make the shelf thicker. Either approach is cleaner than trying to fill a loose dado with glue.