[ralph1]

Hi, I'm grinding a 7 inch mirror and tonight I changed from 80 to 120 grit. I continued using a 'W' stroke, 1/3 overhang roughly and the sagitta went from 1/2 mm to 5/12 mm! I can't understand how this happened as I thought the W stroke increased the sagitta. The only things different were some paint on the edge of the tool which ground off after one wet(I was using it to seal in any rogue 80 particles) and one wet spent grinding tool on top as an experiment. I am using a porcelain tile grinding tool with asupramax glas blank. I'm aiming for 0.8 mm sagitta so stopped 80 at 0.5 to creep up on the right amount. I grind for 1/2 hour at a time. This is my first mirror.
Ralph