Recommended stroke for hogged mirror and tile tool

[Garyh]

Hi Folks,
Just a quick question before I start on my new mirror.
The blank is hogged out to about f/5 (with a old pipe fitting) and I have made a tile tool to suit the shape. The mirror is not very spherical more like a hole in the middle.
Just wondering what stroke would be recommended to get things back more or less to a spherical shape. I am hoping to get the mirror to about f/4.7 when complete.
cheers and thanks for any advice..
Gary

[Satchmo]

Hi Gary
Start by working away the `shoulder' area ( the edge of the hole ) on the edge of the tool, chordal stroke style. Once the curve is looking much more spherical , alternate MOT ( mirror on top) and TOT with say a 1/4 length W stroke until sphericity is obtained. If you want shorter FL spend a bit more time MOT . You can observe the behaviour of trapped air between the blanks to get a handle on their sphericity. Hope this helps.

[Garyh]

Originally Posted by Satchmo

Hi Gary
Start by working away the `shoulder' area ( the edge of the hole ) on the edge of the tool, chordal stroke style. Once the curve is looking much more spherical , alternate MOT ( mirror on top) and TOT with say a 1/4 length W stroke until sphericity is obtained. If you want shorter FL spend a bit more time MOT . You can observe the behaviour of trapped air between the blanks to get a handle on their sphericity. Hope this helps.

Thanks Mark for that info....
using the pipe fitting does hog the middle out well but leaves the edges very flat...shall start with that chordal stroke...
cheers Gary