seen a few crack disc after the drilling.some of them last for years.
i don't know whether to encourage u to do it or not.but if u still
insist on doing it,try check out those X-drill disc first for reference.
u will notice that the upper part of the surface is bigger then the
lower part of the disc.the hole is narrow.meaning is that if u drill
the surface,let say 5mm,the lower part should be around 3-2mm.
like V shape.that will make ur disc much stronger the directly drill
it 5mm from top to bottom.just my 2 cent.