Tear the log in half with a rip saw, and cut one piece down to 3 feet long. Optionally, have this done at a lumber yard.
Sand the slab with the power sander, using 80-grit, then 100, 120, up to 220-grit sand paper. Finish sanding by hand with the 320-grit paper, bringing out the natural beauty and grain of the wood.
Shape the edges of the sanded slab with the drawknife. Soften and smooth the edges, working with the grain of the wood, not cutting against it.
Cut the ash or sapling tree into 4 pieces that are 20 inches long.
Use the drawknife and woodworking chisel to trim one end of each leg into a 1 1/2-inch spindle, a tapered end to insert into routed holes that you'll drill
Turn the slab onto the side that will be the bottom, and measure and mark 3 inches in from each side to place the legs.
Use the power drill and router bit to drill a 2 1/2-inch depression for the legs to fit into at each leg mark on the slab.
Cover the spindle ends of the legs with carpenter's glue and insert them into the leg holes. Tap them with the rubber mallet for a tight fit. Let glue dry for a day.
Apply tung oil if the bench is for outdoor use or light varnish if for indoor use and let dry thoroughly.