Very nicely done! Good design proportions and materials choice! I have been wanting to try some aluminum/MDF sandwiching for some projects too. Where did you source your metal sheet material? I have found it not easy to get in smaller quantities.

The aluminum was sourced from a small / medium sized metal shop in Edmonton. It was just a matter of checking the yellow pages and sending out for some quotes on my specific needs. Though not cheep($430), the 10 pieces of aluminum were cut to exact dimensions, and only needed light filing of the sharp edges.

The aluminum was both glued, using West Epoxy boat adhesive, and screwed with wood screws. Some trial and error was required in mixing sufficient fiber into the epoxy mix, and being careful not to apply too much epoxy.

I modeled the shelves on the computer prior to finalizing the design, aiming for maximum stiffness, and minimum weight. This produces the highest natural frequency and hence the lowest deflection amplitudes. Solid slabs of medium density fibre board proved to be better than either light weight fibre board, or medium density board with holes drilled to reduce the weight. The shelf support points were located at the vibration "null points" (about 22% of the length in from the ends). This prevents the support frame vibrations from being amplified by the shelf.

The most time consuming activity in constructing the shelves was to countersink the screw holes in the aluminum (all work was performed with hand tools). In hind sight I should have ordered a softer grade of metal, which would not affect the dynamic properties.

Hemlock was a good choice for the frame. It is quite a stiff wood, but is softer than say oak. It cut and sanded more like pine than a hard wood. Look for pieces of Hemlock with a tighter grain to limit drill bit drifting. I would have used maple but it was significantly more expensive, and would have required more sophisticated wood working tools.

Thanks for the info and explanations Neil- very helpful!