While testing premium dado sets, we discovered that some sets will make clean, chip-free, cross-grain cuts in veneered materials only if you use them with a zero-clearance insert in your tablesaw. (You'll need a separate insert for each width of dado cut you make.)
You may be wondering how this handy gadget gets its name. Because you raise the running dado set through the insert to make its opening as shown right, there's zero clearance between the side of the set's outside teeth and the insert. The surface of the insert completely supports the veneer of the workpiece and prevents it from chipping as the teeth exit the cut.
To make one, use your saw's metal insert as a template. With double-face tape adhere the metal insert to a piece of plywood, hardboard, or any other stable materials. Use either 1⁄4 " or 1⁄2 " material—whichever is just slightly thinner than your metal insert. Saw just outside the plate and trim the wood insert to the exact shape of the metal insert with a flush-trim bit in your router table (see illustration below). Set the zero-clearance insert flush with your tablesaw top by applying small strips of tape to the underside of the insert where the tablesaw supports it. Hold the insert down with your tablesaw's fence and raise the running dado set through it.
–WOOD magazine shop
Watch Jim Heavey show you how to make a zero-clearance insert.