no point in sanding the holes because as the discs get worn by the pads, the holes will regain the sharp edge.
you should grip the disc in two places - at the spoke and keep that still and at the braking surface which you move to bend the disc. If you do not do that, then you are stessing the mounting hole in the hub so risk snapping it.
I think I'm not explaining myself correctly. It's not just the edges that are sharp. There are very small but really sharp burrs sticking out. (I actually spent half an hour googling until I found the word burr
, as I had no idea hat they were called in English)
Looks like these disks simply weren't finished properly.
Thanks for the tip on holding it in 2 places though, I'll be careful. Looks like the 6 rings are taking up most of the movement while the center piece of the rotor stays straight. however I'm sure there are some forces being transmitted all the way to the mounting holes.
Here's the Hope Saw disc I'm referring to. Mine have a black center though.