The vital instructions are contained within Michael's site (linked above).
The construction steps I followed:
•Sized the .jpg template file in MS Paint and Word so that it printed out at the scale I wanted.
•Printed out several copies of the template.
•Squared out the balsa blocks to the exterior lines of the template.
•Glued a copy of the template top-and-bottom to the blocks.
•Rough-cut the balsa blocks to be just larger than the template curve.
•Freehand-sanded the block to fit the curve. I used a stationary belt sander and moved the pieces by hand.
•Cut the thin aluminum sheet to squares.
•Formed the aluminum into curves. (This is the second-hardest part.)
•Drilled holes the right size and depth to insert the rubber ducks.
•Epoxied the curved metal pieces to the balsa forms. I used packing tape and light clamps to hold them in place. (This was the hardest part. If I were doing it again I would first make some kind of a clamping jig first.)
A good lock will keep an honest man out.