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How do I make smooth-bottomed dadoes?

Q:

How can I cut dadoes with smooth, even bottoms using my tablesaw dado set? My set leaves ridges even though I just had it sharpened.
—Walter McCoy, Salina, Kan.

A:

Unfortunately, Walter, very few stacked dado sets leave a perfectly smooth, flat channel, even when brand new. In most cases, it’s not a big deal because you’ll never see the joint after you’ve assembled the project. But when you need it dead flat, use a dado cleanout bit, shown above, in your handheld router. These bits have a shallow cutter, 18 " to 14 " in thickness, leaving room on the dado’s shoulder for the bearing to register against. If your dado needs to be a specific depth upon completion, be sure to deduct the to-be-routed depth when setting the height of your stacked dado set.

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The stacked dado set that cut this channel left ridges in the bottom caused by slight height variances between chippers and blades.

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The remove the ridges, set a cleanout bit to shave 1⁄32" or so from the dado bottom. Holding the bearing against the shoulder, rout down and back.

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