All the finer grit sizes will be used to get rid of the pits formed by the previous grit size. Since the grinding machine produces random motions, the resulting surface must be approximately spherical. As the grinding progressed, we needed to make sure the curvature was staying approximately correct. Jim Sattler used his spherometer to measure the curvature. At one point early in the grinding process, it became obvious that one mirror was significantly shallower than the other, which would be difficult to correct with our current methods, so we went back to the curve generator stage with that mirror to correct it quickly.
Patience is a virtue, or so they say.
Unfortunately, if you wait for the simple weight of the mirror against the grit and tool to get rid of the radial lines, then death will come shortly before those lines are ground out. The machine turned the mirror and we all took turns manually moving the tool. Later we proved we were smarter than the machine by putting weights on top of the tool to increase the pressure and putting the alligator back on so the machine would move the tool. Back to optics index .