Im a new machinist and am new to grinding although i've studied it. I wanna learn how to shave and grind cylinder heads but my automechanics teacher, not a machinist himself, says that u have to grind in one pass with a huge grinder otherwise if u make multiple passes it leaves "lines". Im talking about grinding on a 1.5hp milling machine since my shop and budget arent big enough for a huge machine. It doesnt make sense to me that if everything else is done right, that it would be impossible to grind a uniformly flat surface with more than one pass.