Hello!! It's Joseph

mirror size: 406 mm tool size: 330 mm simulation with Tool on top, moving along x direction, changing chordal stroke parameters:    Effect of varying stroke,  y offset kept same (center of Tool above edge of Mirror) 1a) y offset of 185mm, stroke 102 mm   1b) y offset of 185mm, stroke 135 mm ( I use this to grind down the untouched mirror edge) xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Effect of varying y offset, keeping same stroke. for rough and fine grinding, Mel Bartels suggests to use 1/3 W to 1/2 W, ( ie varies y offset from 1/3 D to 1/2 D travel) continuously, with stroke ( x direction) kept at 1/3D. D is diameter of mirror(NB this W stroke is different from w stroke used in polishing and parabolizing, eg in stellafane ) :   In rough grinding: When you reach 2/3 of the desired depth( by hogging with a metal tool), flip the mirror face up. You will see that the edge of the mirror has hardly been touched.  Put the tool on...

For fine grinding starting from 220 grit and finer, the normal 1/3D stroke used is shown in Fig 8. the mirror is centered over the tool and the stroke is a W-type stroke with a total lateral amplitude of ¼D (i.e. 1.8 cm on either side of the centre for a 15 cm mirror) and an up and down amplitude of about 1/3D (i.e. about 2.5 cm up, 2.5 cm down for a 15 cm mirror). It should be 1/3D on the average; some strokes should be a little shorter and some a little longer. No attempt should be made to make the strokes uniformly 1/3D in amplitude. The 120 0 rotations of the blank above and the 45 0 rotations of the blank below are of course continued. the wet now lasts longer, say for 4 or 5 minutes. At the completion of a wet the mirror and tool are cleaned as before and a fresh charge used. Shankar