The function of a woodworking jig is to keep your hands away from dangerous machinery when shaping, cutting or sanding wooden parts. Parts also need to be held securely to the jig to prevent them from flying out or kicking back. Adjustable hold-down knobs are installed on top of the woodworking jig to accomplish this. Hold-down knobs can be made from items you may already have in your shop or garage.
Draw a letter "C" on the wood blank lengthwise, but leave the ends and back square. The curved back edge of the "C" shape is the top of the knob where you grab it.
Lay the "C" shape on its points, with the back facing up. Drill straight down through the top of the back using the cordless drill and a 3/16-inch bit.
Place the washer on the screw and then insert the screw through the hole.
Place the knob on the jig, with one point of the "C" shape extending out over the edge of the jig. Screw the screw down into the jig, but leave it loose enough so that the knob will spin around in a circle.
Place your jig on a shaper table. Place the object to be shaped on the shaper table in its location in the jig. Swivel the knob over the handle. Use the cordless drill to tighten the screw to compress the knob against the object to hold it tight.
This example is for objects that are mounted to the jig flushed with the top of the jig. For objects that are at a higher elevation than the jig, cut one arm of the "C" shape off shorter. Place sticky sandpaper on the contact points of the "C" shape to further prevent slipping.
Always make sure your knobs are tight before using your jig. Always wear safety glasses when working with wood and machines.