I mounted the PCB board on a piece of 3mm acrylic glass with some double sided carpet tape, the type without the foam core. I use these quite often to put under my workpiece. They are cheap (leftovers) and very flat and smooth.
I found that the trick is to apply a nice smooth surface of tape to sick your workpiece to. Covering the entire surface will prevent any warping of the prototype board.
Next I clamped it down on my milling table.
All programs are aligned to the centre of the ring
Load the 2nd code file for the 2mm flat end mill to check the clearance.
Load the first program named 1ringlight engrave.nc
Insert a 45degree engraving stylus or a 0.5mm centercutting flat end mill, touch off the top of the stock as z0
set a spindle speed of 5000rpm and a feed speed of 300mm min
in my case I used an engraving stylus so I set the plunge rate also at 300mm/min
After running the first program
Change tools, insert a centercutting 2mm flat end mill
touch off the top of the stock as z0
Spindle speed 5000rpm
feed speed 300mm/min
plunge rate 300mm/min
After running the programs it is time to dust everything off and unstick your ring.
Note that all programs have a higher feed rate, I have used these programs at 50% of the feed speed.