Is that a regular black/composite cutting disc?
I jumped on ebay and ordered some diamond cutting discs, i don't expect them to arrive anytime soon but when they do they'll be nice to have.
its brownish or reddish. this thing is really fragile on hand or if you accidentally hit it with your finger while its on the shaft holder. i keep breaking them (not while cutting). so i bought 1 pack original dremel disc 36 pieces
like this as long as you handle them like ESD sensitive RF component, they should be alright at cutting many pcb until they run small in diameter. i tried steel disc with sawtooth, that was a big no no, the teeth can stucked on pcb throwing it away, that can be dangerous. i havent tried diamond (steel like) disc. the black (fiberglass reinforced) disc, i have the stock but never tried it i suspect it will run poorer, i think the brownish disc is superb enough at cutting material like pcb laminate. the key here is the sliding table, try cutting with hand will be a PITA, not to mention countless disc you are going to break. ymmv.
I wonder would it be worth it to prefill the vias with solder to avoid tearout?
can be a good idea too but i havent tried, imho higher speed disc rotation and slowly cutting thin layers in few passes may do the trick. looking at the zoomed picture earlier, the holes plating already covered with solder from factory, so i guess its hard enough from tear out while being cut.