Hogging out a flat surface blank for a 40 cm f/4.5 mirror on the Mirror-o-Matic

Tools used: 240 mm diameter tool, glass tiles on alumium disk and 300 mm diameter tool, glass tiles on dental plaster. Grit used: Carborundum #80 and carborundum #180. At the end of 180 grit the mirror will not be perfectly spherical (high center), but will get perfectly spherical during fine grinding.