Create the front and side of the drawer. Butt one 6-inch piece up against the edge of your 4-inch piece. They should make a right angle. The 4-inch piece is the front, and the 6-inch piece is the back. Make sure the edge is flush. Put a small bead of wood glue on the edge. Balsa wood is very soft and malleable. So when your 6-inch piece has been butted and glued, merely take a finishing nail and push it into the front of the 4-inch piece with your fingers, and push it into the butted 6-inch piece. Make a line of four nails top to bottom. This will hold the 6-inch piece and the 4-inch piece together.
Add the other side and the back of the drawer. On the other side, join both the 6- and 4-inch pieces together, glue and then push in four finishing nails to hold them. On the back, place your remaining 4-inch piece over the back of the 6-inch pieces, glue and push nails to hold the butt joints together.
Attach the bottom. Turn your drawer over so that the bottom is facing up. Your 6 x 4-inch balsa sheet should completely cover the bottom. Lay down a small bead of glue and press your sheet onto it. Once again, using about six finishing nails per side, just press them in place to hold the sheet down.
Add the knob. Stand your drawer up on its back. Now you are ready to put on the wooden knob. Take your straight edge and then draw a line corner to corner diagonally with your pencil. Where the lines intersect is your center. Put a dab of glue in the exact center and put your drawer knob on top of that. Allow the entire drawer to dry over night.
Use the 150-grit sandpaper to sand over all the edges and uneven parts until everything is flush and smooth. Use a light touch because balsa wood is very soft. You can now use your drawer as an independent accent piece or add it to a larger piece of furniture.