1 Measure and mark the centre of the other sheet of ply. Lightly hammer a short nail part way into the mark.
Measure and cut a piece of string about 400mm. Attach one end to the nail and tie the other end around a pencil, ensuring the string length is 300mm when attached to both.
Stretching string tight, draw a circle (600mm diameter) around the nail. 4 Remove nail and string and use a jigsaw to cut out the circle.
Draw a line down the middle of the circle. Cut along line with handsaw.
Lay one half-circle flat and stand the other on top of it to form shelf. Glue and screw the 2 pieces together with 32mm screws. Sand off edges.