Also for those who aren't familiar, there's also "hand scraping" for flatness which is more common and used for things like refreshing the "ways" (ie precision linear bearings) on a lathe or other precision machine tool.

This is done like the "dye / rub / scrape" method described above, which I believe is still used as it's superior to grinding for these applications.

See video below for the process: https://www.youtube.com/watch?v=T7w84CrBEE8