The trickiest stretch here was not the turning itself but the wait: the second set of ordered bearings arrived late, and only then could the decorating tool be finished. The maker pushed through and completed both halves of the project, a cherry top and the homemade grooving tool used on it, in the end.
The top itself came off the lathe in roughly thirty minutes, shaped with a small bowl gouge. It has a tapered stem, a bulbous collar, and a carved hatched pattern around the disk, with grooves between the rings cut using the new tool. During the spin it settles into an upright, balanced rotation on a wooden desk, drifting slightly toward a keyboard before finding its spot, all with a steady mechanical buzz from the tip.
The tool is the part that stands out for me. A quarter inch steel tube holds a dowel rod that fills the empty space and carries two disk magnets, with spacers cut from a soda can plus multiple roller bearings inside. The bearing bore is one eighth inch, so standard one eighth inch shank bits fit, and a standard Dremel carving bit does the cutting. The handle came from red maple in the maker's front yard, which is quite hard, stringy, and has interesting grain. The commercial version of this kind of tool, the decorating elf, runs near one hundred dollars with bits; the parts here cost about forty, or about thirty two without the spare bit pack, and a second build would drop the per tool cost to around twenty.
One open question is the tip. A polished tip prevents scratching the surface, and the maker is weighing a small hard metal roller bearing pin as a tip on future tops. That choice is still up in the air.