The KM-1 Kerfmaker is an innovative tool that is precision machined from anodized aluminum, which won't rust. It simplifies the process of making accurately sized grooves, dados and half lap joints. Even half lap joints that are not at a 90° angle are very easy to make with this tool. It works with any cutter that leaves a clean, repeatable kerf, such as table saws, router tables, or the Jointmaker Pro. The concept is that rather than trying to fuss with fence movement or make tiny adjustments to dado head widths, the KM-1 is used as a flip-stop to provide a precise offset for cutting both sides of the groove.
To use it, a sliding arm on the KM-1 is adjusted to the exact width of the cutter. Then another sliding arm is adjusted to the exact required width using the stock as a gauge. After these adjustments, the KM-1 is used as a spacer against a fixed stop to cut one side of the groove. It is then flipped to create an offset to cut the other side of the groove. In cases where the groove width is more than twice that of the cutter, any waste in the center between the two groove edges is removed with additional cuts.
If you are using the KM-1 on multiple machines or with different cutters, it is possible to make set up blocks, which allow the cutting width adjustment to be done in moments. To see how this works in more detail, there are several very good videos on youtube showing how it works. It is perfect for cutting grooves for sheet goods, which often vary in size, as well as box making, shoji screens, drawer making and half lap joints.