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I cut dados for a tight fit. When I make them too tight, I use a jig that I call a Dado Tuner.
The sole is 1⁄2” Baltic birch plywood, measuring 41⁄2“ x 12″; the open slot is 1″ x 6″; and the adjustable sanding fence is 3″ x 6″. The body and handle were shaped from one piece of 11⁄8“ hardwood. The portion of the body to which the fence is attached measures 21⁄2“ x 71⁄2“. The handle is sized to fit the user.
The turned knob is offset to the right to help maintain pressure as the sandpaper is pressed against the dado’s wall.
The sanding fence is made from 1⁄8“-thick white hardboard, which is available from big box stores. Its shiny surface makes it easy to adhere and remove adhesive-backed sandpaper. The fence is held to the jig’s body with 1⁄4“-20 knurled brass thumbscrews that are screwed into threaded inserts. The slots in the fence are a little more than 1⁄4“-wide and 1″-long.
To use the jig, place it on top of the dado, loosen the brass nuts and slide the sanding fence into the dado until it sits flush with the bottom. Tighten the nuts, press the sandpaper surface against one wall of the dado, and slide the jig from one end of the dado to the other. A few quick strokes increases the dado’s width, and the wall will be evenly sanded from top to bottom and along its length. –Don Henderson
