Cutting wide dadoes efficiently

Q: Every time I use a dado set to cut half-lap joints, I seem to waste a lot of time lining up each successive cut to the edge of the blade. Is there a faster system?
—Pat Martin, Oak Park, Ill.

A: Here's a way that will save you time and energy, Pat. First, screw a plywood auxiliary extension to your tablesaw's miter gauge, and slide it once through the running dado blade to show you the edges of the cut. Use a pencil and square to draw a reference line from one edge of the cut up the face of the fence. Then make a series of evenly spaced marks away from your reference line along the face of the extension. Space these marks slightly less than the width of the dado cut, for example ¹¹⁄₁₆ " apart for a ³⁄₄ " dado. Then make a single indexing mark on a strip of tape on the back of each workpiece to identify where your cut should start. Move that mark on the board to the next mark on the extension for each successive cut until you reach the other edge of your half-lap.