Re: ATM polishing help needed

[hermit <hermit@outofoptions.com>]

Common mistake.  1/3 stroke means 1/6 overhang in each direction, or 1/3
diameter total travel.

So, for a 6 inch mirror, you would move the work piece 2 inches total.  It would
overhang 1 inch on each side, or 1/6 of the diameter.

If you go too long, you turn the edge severly.  Now would be a good time to do a
Ronchi test and see if the lines are straight in the middle where  it is
polished.  If they are strongly bowed, you used too long of a stroke and will
have to go back to fine grinding.  If the lines are straight or just weakly
curved in the middle, put the mirror on bottom and polish that way.  It will
work the edge more.

Ken



Quoting Old Salt Fish <oldsaltfish@hotmail.com>:

>
> Greetings to all,
>     I keep polishing for more than 2 weeks and still can't finished it.
> Even the surface is clarity already, but the edge is still dim if put a lamp
> after it, many micrometers pinholes, the center is clear but many larger
> pinholes(about 0.1 mm each). very depression!
> the picture can be found at here
> http://amateur.lamost.org/bootes/bbs/attachment.php?s=&postid=150042
>
> Do you have any good suggestion? many thanks!
> BTW:I am using Fe2O3 and beeswax, 1/3 diameter W stroke and elliptical
> stroke, the mirror is 250mm in diameter,F/4
>
>
>
> Best Regards,
> Old Salt Fish
>
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Hermit
Holed up in Youngstown, Ohio