Re: [ATM] 16 1/2" mirror grinding-NEED HELP

[Jarvis Krumbein <jkoptic@juno.com>]

Hi Bob,

It sounds like you are at the point where it's time to make a new full
(or near) full size tool.  If the grind is now out to the edge then make
a tile tool to conform to the shape of the hogged out mirror and continue
with 60 grit (80 would probably be better) with the tool on top and
fairly well offset until the center depth is around .190.  This should
wear in and true up the new tool and get you close to spherical.  Change
to center over center strokes with about a 6" stroke until a sharpie test
shows good contact and spherical surface.  Switch to your next finer
grade of abrasive and continue.  Alternate tool on top/mirror on top when
proper depth is reached in the center to maintain the desired depth. 
You're on the right track.

Good luck,

Jarvis Krumbein

 
On Wed, 17 Jan 2007 20:13:08 -0500 horace r davis <hrd9@juno.com> writes:
> appreciate input on type of strokes to get the desired f5 focal 
> length
>     center depth .200
>     Telescope mirror log 16.5 inch mirror
>     Started Jan 2007
>     Tool: 5 inch diameter pipe phalange
>     Beveled edge 1 hr
>     Hogging out mirror
>     2 hr first light center under straight edge
>     4 hr not using enough grit less .05
>     3 hr increased grit center depth .069
>     1 hr center depth .076
>     10 hr
>     1 hr center depth .089
>     1 hr center depth .106
>     1.5 hr center depth .120
>     Center 2/3 of mirror was hogged out buy the other 1/3 not 
> touched
>     Increased length of stroke to reach the edge
>     2 hr center depth .149
>     1 lb * 60 grit used at this time
>     17 Jan 15.5 hr
>  
>     Thank you,
>     Bob Davis
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