Got to work with the file..
I tried a variety of dremel bits, but the steel used on these disks is quite hard.. the best solution was a round file ( Used to sharpen Chainsaw tips !! ) .. i have a bunch of them from all sizes.. started with the smaller one and worked my way up until i made the marker marks.. disapear.
Keep lubricating the file with WD-40 or cutting oil if you have some handy.