Same content, but this link might be a little quicker: https://archive.org/details/engineeringremin00port/page/233/mode/1up https://archive.org/details/engineer

Same content, but this link might be a little quicker: https://archive.org/details/engineeringremin00port/page/233/mode/1up https://archive.org/details/engineeringremin00port/page/233/... If you're interested in the topic, here's some more discussion: https://www.practicalmachinist.com/vb/general/possible-make-grind-polish-flat-surfaces-manually-295976/#post2441051 https://www.practicalmachinist.com/vb/general/possible-make-... Skilled hand scrapers... can generate plane surfaces accurate to 40 millionts per foot. The same method applied to lapping of glass can generate flats to 1/2 millionth per foot... The average guy working in an open shop careful of cleanliness and uncontrolled heat input to the work will find 0.0005 per foot readily achievable and 0.0002" per foot with a little more care and effort.