Re: [ATM] Adjusting FL During Fine Grinding

["Bob May" <rmay@nethere.com>]

Sounds like you need to put the mirror on the bottom and do some
grinding to bring the ROC back out.  I'll note that when you get
to the 220 grit, the spherometer should be reading the same thing
all over the surface.
I'll note that I've also put up the two formulas that basically
generate that chart - the chart is just the outupt from a
spreadsheet program.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: Bill Wheaton <junkwheaton@gmail.com>
To: ATM list <atm@atmlist.net>
Sent: Saturday, May 17, 2008 9:32 AM
Subject: [ATM] Adjusting FL During Fine Grinding


> I'm about to start my fine grinding on my 12.5 inch.  But I
ground more than
> I intended and the FL is now at 62.75" (as measured with a
wetted mirror in
> the sun a few minutes ago).
>
> That's f/5.0, and my target is f5.5 or 68.75". and that roughly
jives with
> the measurements I've made with my 6" ring sphereometer.
 0.0320 at edge to
> 0.350 at center ).  I've gotta say that Bob May's sagitta
> chart<http://bobmay.astronomy.net/misc/sagchart.htm>has been so
handy
> for me to bracket my measurements.
>
> So, to get it to my target FL, should I continue with the metal
tools and
> try to flatten it out more, or is that something that will get
longer (or
> shorter) when I start to fine grind?  I have read that it will
actually tend
> to get shorter with MOT, so I was thinking that I would start
the new tile
> tool with TOT until I reach my desired FL and the tiles are
mostly in
> contact.
>
> Does that sound logical?
>
> Hopefully this will be the last of my newbie questions for a
while.  I had
> forgotten how far apart "book learning" and "hands-on" can
really be.
> Thanks,
> Bill
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>

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