Teapot lid (Q910363)

A while ago I broke the lid of my beloved teapot (it's been in the family for over two decades). So I made a new one with my Prusa. This was an opportunity to try a fun new workflow. The lid has radial symmetry (its group is O(2) for the mathematically inclined), making it a good job for OpenSCAD's rotate_extrude. To get the appropriate outline to extrude I used Inkscape, tracing by eye with the aid of a photo. The Inkscape to OpenSCAD extension did the rest of the heavy lifting. I added some support material for the lid's "lip" and knob; this should detach easily. One of the challenging aspects was cutting a small notch in the knob support in OpenSCAD, as there is no support for partial rotate_extrude built-in.