I have a couple of these “slaves” mounted under my workbench top to allow for easy clamp-free support of long stock for edge planing. Each unit is basically a bracket that houses a stick that can be extended for board support when necessary, and retracted when not in use. These slaves are simple to build, as shown. Just make sure to use a strong hardwood such as maple or birch for the bracket, and an even stronger wood, such as rosewood or osage orange for the stick. After shaping the center block and gluing it between the outer blocks, drill and counterbore clearance holes in the outer blocks and screw the bracket to the underside of your bench. Make sure that the retracted stick is inset about 1/2" from the edge of the bench. Consider mounting one slave in the middle of your bench, and one at the far end opposite the vise to accommodate boards of various lengths.
—Andy Rae, Asheville, North Carolina