> The state of the art (and has been for eons) is hand scraping
No, it absolutely is not. Optics machine tools make things flat and accurate within a few atoms. Cheap surface plates are more precise than any human could hope to achieve by hand.
Hand scraping is remarkable- skill can get you ~micron cutting depth. It would be totally obsolete except that the rough crosshatch pattern it creates is useful for retaining oil. Modern tools, especially the most precise tools, are not hand scraped. Cheap clone knee mills are hand scraped. Single-point diamond cutters run on air bearings with no oil, because the oil gap in plain ways is too large.
Hand scraping is thoroughly limited by the viscosity of the marking fluid. You identify high spots by painting a flat blue and rubbing it on another flat part. If the whole surface rubs off then you can't tell where to scrape. The fluid does not spread out in single atom thickness.
No, it absolutely is not. Optics machine tools make things flat and accurate within a few atoms. Cheap surface plates are more precise than any human could hope to achieve by hand.
Hand scraping is remarkable- skill can get you ~micron cutting depth. It would be totally obsolete except that the rough crosshatch pattern it creates is useful for retaining oil. Modern tools, especially the most precise tools, are not hand scraped. Cheap clone knee mills are hand scraped. Single-point diamond cutters run on air bearings with no oil, because the oil gap in plain ways is too large.
Hand scraping is thoroughly limited by the viscosity of the marking fluid. You identify high spots by painting a flat blue and rubbing it on another flat part. If the whole surface rubs off then you can't tell where to scrape. The fluid does not spread out in single atom thickness.