An older-model drafting T-square—the kind with a wooden and plastic crosspiece—makes a great fence for routing dadoes for shelves in cabinet sides. To customize the T-square for quick setup, clamp it on a piece of scrap wood and make a short, shallow pass with a dado bit to cut a notch in the crosspiece. To use, just mark the dado locations on the work-piece, then clamp both ends of the T-square in place, lining up the notch with your marks. Now run the router along the blade of the T-square to cut the dado. Unclamp and slide the T-square to the next mark, again using the notch to line up the dado cut.