One machine shop where I worked had a big hardened steel surface plate with a crosshatch pattern of grooves a few thousandths deep in it. We used it with fine grit valve grinding compound in the grooves to lap surfaces to become totally flat.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!