OK, I'm kind of intrigued and baffled by all this sole flattening.
I'm intrigued, because the level of accuracy people are striving for seems to be far greater than anything needed in normal woodworking. I could see maybe having one or two smoothers capable of shaving a couple thou in thickness as a final pass, but a jack plane or jointer? no way, those planes are for taking off material quick. You don't need to have a sole flat to 0.003 to do that. The whole measuring your shaving with a micrometer thing seems like it started around the time of the internet. . . . .
I'm baffled, because when I read threads and see videos and articles on sole flattening, people are typically using things to both measure and flatten (plain steel or aluminum rules, granite tile from Home Depot, glass on a workbench, table saw wings) that are not nearly as accurate as the accuracy that they are striving for. Not to mention not close to being rigid enough to maintain that flatness with someone pushing a plane across them. To accurately measure a plane sole to a couple thousands, you need an actual surface plate or machinists straight edge, and machinists tools. When you look at lists of woodworkers tools of yore, you don't see surface plates, feeler gauges, 1-2-3 blocks, micrometers, or lapping compound. Why is it that they are suddenly needed now?
So I am truly curious, how flat do folks think their planes need to be (and why)?
And now I am ducking before people start hurling their LA jack planes, high frog smoothers, bronze bodied planes, and thick irons at me