(the smaller one is the first one I made; I worked out a simpler way to approximate the ratios needed and made the larger one.)
I record this accomplishment here for posterity so at least I don't forget I did it. I wrote down the instructions and everything too so maybe it could be repeated. I suppose for some people working this out would be simple, but what I think is cool is how little I started with. I had done none of the calculations to find shortcuts and formulas for all this, and besides, it isn't like my 3D geometry is even all that good. I remember a few simple formulæ from plane geometry and trigonometry and that's about all I have to go on; I re-derive everything when I need it. I couldn't even find good data on the shapes of the triangles etc (actually, MathWorld did tell me the edge lengths, but I didn't even look at them so I didn't realize how easy it was to derive their very simple 4:3 ratio); I derived everything from only the description of the shape as a cube with each face replaced with a pyramid of height ¼s. Hey, I thought it was cool.