A diamond point drag engraving bit in the MPCNC scratched a suitable Guilloché pattern into a scrap hard drive platter much much better than I had any reason to expect:
That’s with a 0.1 mm cut depth, sidelit with an LED flashlight.
Feeding those nine digits into the Guilloché pattern generator script should get you the same pattern; set the paper size to 109 mm and use Pen=0 to suppress the legend.
The same pattern at 0.3 mm cut depth looks about the same:
It’s slightly more prominent in real life, but not by enough to make a big difference. I should try a graduated series of tests, of course, which will require harvesting a few more platters from dead drives.
Either side will look great under a 21HB5A tube, although the disks are fingerprint and dust magnets beyond compare.
The Smell of Molten Projects in the Morning 