I find your videos very informative. I have same thing on my plan for the next summer.
I have worn Mahr 800*600 mm granite plate. Thinking of using that one to scrape disc brake rotor relatively flat, then sprincle that with diamond flour and lap the offending granite plate bit more flat.
Yesterday I was wotking on grinder guard to make the parts for repeatometerkind of tool.
You probably said, but how coarse diamond dust did you use?
Thank you,
Pekka