Grinding photo-etched brakes

[Tombag]

Hey guys,

I'm currently working on a scale motorcycle project (in model motorcycle WIP section) for which I got some photo-etched brake discs. I found out a little too late that the discs are a little bit too big so I need to grind them down a bit; How would be best to do this?

I don't have a whole lot of tools available to me but I'm sure I could find stuff if I need to, my first - extremely amateur - instinct is to attach the disc to a drill somehow then grind it against something that way. Mainly because it would be cheap and cheerful / hopefully get the job done but at the same time it could be a very flawed makeshift method of going about things...

Cheers!
Tom