The solid that you get by taking the intersection of three cylinders at right angles to each other, is one of the ideas that's been kicking around in my head for a long time.
Figuring out how the peices should be shaped took a lot of scrap paper; I ended up doing all the math right in the postscript code, which is here. Six copies of it are needed.
The ribs are supposed to be parallel, but they deform easily, and I am dissatisfied with the quality of construction. I had gotten somewhat bored with it before it was done, and it kicked about my room unphotographed for about a year. Maybe sometime when I want something tedious to do, I'll give it that second coat of paint.
Here's how it looked as a work in progress.