Hand Scraping a Truly Flat Plane (1908) [pdf]
Not flat but similar idea<p><a href="https://www.cmog.org/article/hale-reflecting-telescope-palomar" rel="nofollow">https://www.cmog.org/article/hale-reflecting-telescope-palom...</a><p>Imagine hand grinding telescope lenses<p><a href="https://www.youtube.com/watch?v=MjUcBWYVF9s" rel="nofollow">https://www.youtube.com/watch?v=MjUcBWYVF9s</a>