My son and I collaborated on this first attempt at a lampshade. I think it turned out pretty nice-looking, although I'm rethinking how to hang it. Uses an IKEA Hemma lamp cord set.
Feel free to remix it. The design on Onshape is public: https://cad.onshape.com/documents/ed3ba8ac23112729f12f1a4b/w/868b0e525ca0b785b1aae52f/e/060213c256d1f59be575a5ae?renderMode=0&uiState=6591c9af8725f6147bd8040d