When I took a tour of the Starrett plant in Athol a few years ago, I actually saw them doing this.....
A row of guys sitting at benches, with a geared "speeder" setup they can clamp a micrometer in and turn the spindle quickly. They apply some very watery (though I assume it's really thin oil, not water) lapping compound, spin the spindle, test the "feel," take out the spindle and bang it on a lead block if it feels slightly mis-aligned...repeat until they're satisfied. They are FAST -- no more than a couple minutes a micrometer, as I recall. But they are truly hand-fitted. I would hesitate to do it myself. Those guys have had a lot of practice.
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