I built the sinc function to see if circles were doing better after re-tensioning the belts, although this was before I replaced the X axis stepper. If you look carefully, you can see the defined-out-of-existence singularity emerging from the exact dead center of the central peak.
My Shop Assistant took it to school, where her math teacher now thinks having a 3D printer would be an asset…
Anyhow, this view of the first ring shows some blobs that may be coming from Reversal, which is at 25 rpm / 90 ms / 90 ms / no early turn-on or turn-off.
Building the central peak above the ring took forever, as Cool limited the speed to ensure each layer took 15 seconds. The last few layers had those stepper. LEDs. Blinking. At. Less. Than. Walking. Speed.
Now, what would Barbie use this thing for, anyway?
The Smell of Molten Projects in the Morning 
If you have to ask that question about a pink, protruding object on the Internet, you *definitely* don’t want to know the answer…
Verily, woe betide those either convex or concave…