Using your screwdrivers, wedges and hammer, remove the existing shelf ledge. If the ledge has an attached backboard support leave it on. Set the ledge and backboard support, if any, aside.
Use the measuring tape to find the center of the 1-by-2-inch board. Use the pencil and carpenter's square to draw a right angle line across the middle of the board.
Use the saw to cut two easel slides to the length of the ledge from the 1-by-2-inch board. Use the sandpaper to smooth the cut boards. Use the sandpaper to round sharp exposed edges.
Lay the easel slides flat and use the measuring tape and pencil to mark four points 10 inches from each end. The marks should be centered to the nearest edges.
Use the drill to make four holes in the easel slides on the four marked spots. After each hole is drilled, ream the hole out slightly with the drill to make the holes slightly larger.
Place the easel shelf (or shelf and backboard if your easel had one) on the narrow edge of one of the easel slides. Use the drill and the 1/8-inch drill bit to make pilot holes for the two 1/4-inch No. 8 screws. Use the screwdriver and carpenter's glue to attach the ledge to the easel slide.
Insert the two 3/8-inch carriage bolts through the holes in the easel slide to which the ledge is attached. This is the front easel slide.
Hold the front easel slide against the front of the easel. Put the back easel slide behind the legs and fit the protruding bolts through the 3/8-inch holes in the back easel slide.
Attach the two 3/8-inch carriage bolts to the two 3/8-inch wing nuts and tighten by hand until just firm.
Slide the easel slides and shelf up or down into the position you desire. Tighten the thumb screws tightly.