I'm always on the lookout for new design techniques for use with waterjet cut parts, particularly ones that let us make parts that break out of the world of 90 degree angles and flat planes. The curvy assembly you see above was made using only waterjet cut aluminum parts and off the shelf hardware.
If you haven't read any of our other articles on how to design parts for waterjet cutting, now would be a good time to read that in order to understand the limitations of waterjet cutting and some ways these limitations can be overcome.
The assembly takes advantage of the fact that the curved top plate is made from flexible yet strong aluminum 5052 alloy in 0.025 inch (0.64 mm) thickness. Since it's slightly thinner than a credit card, the aluminum rectangle can be bent by hand.
The flowing lines of the curve were created in Inkscape, then imported into LibreCAD.
The spacing of the holes on the rectangular plate was determined by drawing a spline curve along the support plate outline between two t-nut slots, then using the "Total Length Of Selected Entities" menu option. The holes were then placed this distance apart on the rectantgular plate.
Below you can see the unassembled support plates and top plate. The support plates are made from thicker aluminum: 0.125 inch (3.18 mm) thick aluminum 6061.
When creating this type of assembly, I recommend installing all of the nuts first before attempting to attach the screws. You can use superglue to hold the nuts in place during assembly.
I assembled the pieces one support plate at a time, but I suspect it would be easier to alternate attaching the screws between the two suport plates. It would also help to have the support plates held apart at a fixed distance from each other, which I didn't do.
Here is a view from underneath the assembled pieces.
Finally, I will note that it did require a good amount of finger strength to push the plate into place before screwing it down. This was mostly a problem as the curve reversed its direction. I suspect that a curve that went all to the inside or all to the outside would be much easier to assemble.