A kerfmaker is an awesome tool to make. If you haven’t already, you need to click on this link and make one for your shop. It is essentially a measuring device. To make a perfect fitting dado you need to know the correct distance to move the work piece from start to finish. A kerfmaker provides this distance without ever measuring. The same technique can be used with a stop block. Take a scrap piece or a cut-off from the material you are using. Set the height of the blade to half the thickness of your material and the distance for the fence should be set to remove only the thickness of the blade. Once set, make a cut in the scrap piece. The resulting piece will have the exact distance you need to travel to make a perfect fitting dado with the corresponding blade in the saw. Here are a few example videos showing the setup. The Keek video is from my current project. The second video is from the shoji frame build where I used the same setup.