Re: [ATM] ATM Digest, Vol 50, Issue 31

[<gregj888@comcast.net>]

Hi all

I'm traveling and will be back Thur.

Better email -  gregj@eclipse-t.com

Greg Jones
503.442.2928

-----Original Message-----

From:  atm-request@atmlist.net
Subj:  ATM Digest, Vol 50, Issue 31
Date:  Tue Feb 26, 2008 5:00 pm
Size:  3K
To:  atm@atmlist.net

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Today's Topics:

   1. Re: subdiameter lap controversies? (Scott Ewart)
   2. Re: draper (Dominic-Luc Webb)
   3. Help my 17.5 inch coulter mirror is astigmatic (Carl Vehmeyer)
   4. Re: Help my 17.5 inch coulter mirror is astigmatic
      (astroguy@nas.com)
   5. Re: subdiameter lap controversies? (Mike Lockwood)
   6. Re: Help my 17.5 inch coulter mirror is astigmatic (Carl Vehmeyer)
   7. Re: Help my 17.5 inch coulter mirror is astigmatic (kreig)
   8. Re: Help my 17.5 inch coulter mirror is astigmatic
      (Francis J. O'Reilly)
   9. Re: Help my 17.5 inch coulter mirror is astigmatic
      (Charles Broward)
  10. Re: Help my 17.5 inch coulter mirror is astigmatic
      (Jarvis Krumbein)
  11. Re: Help my 17.5 inch coulter mirror is astigmatic (kreig)
  12. Re: Cassegrain Secondary Magnification (Arjan te Marvelde)
  13. OH B*****KS (Neil Booker)
  14. Re: Cassegrain Secondary Magnification (Alfredo Rainho Neves)
  15. Re: OH B*****KS (Jarvis Krumbein)
  16. Re: Help my 17.5 inch coulter mirror is astigmatic (Carl Vehmeyer)
  17. Re: Cassegrain Secondary Magnification (Rod Brackenridge)
  18. Re: Help my 17.5 inch coulter mirror is astigmatic (Scott Ewart)
  19. Re: Help my 17.5 inch coulter mirror is astigmatic (Don R Surles)


----------------------------------------------------------------------

Message: 1
Date: Tue, 26 Feb 2008 00:30:19 -0500
From: "Scott Ewart" <scotte@frontiernet.net>
Subject: Re: [ATM] subdiameter lap controversies?
To: <atm@atmlist.net>
Message-ID: <00e201c87838$ad4d5fd0$07e81f70$@net>
Content-Type: text/plain;	charset="us-ascii"

Bob,
	I'm just trying to save him some time.  When I made my 12.4", I
never got very close to a sphere and never tried.  If I started to go in
that direction, I changed direction.  My goal was only a paraboloid.  When I
got a zone, I worked on fixing it.  I turned the edge more than once, then I
fixed it.  I think I went through 5 different sized tools along the way.  It
turned out the 10" worked best, at least for me.  And yes, I was overcorrect
a few times too.  Getting everything fixed all at once was the trick.  But I
did persist and my mirror does test at 1/20th wave.
	I suppose there are those with experience that may be able to easily
figure a smooth sphere, then quickly proceed to a smooth paraboloid.  I envy
those people, but I'll never make enough mirrors to reach the level of
control and consistency.  As the first-timer I was though, I doubt that I
could have made a decent sphere any quicker than a paraboloid, and I suspect
many ATMs are in the same category.  That's why I don't recommend spending
time chasing two goals.  I think experienced mirror makers may like to start
from a sphere because it's quicker for them, but that doesn't mean it's best
for everyone.

Scott Ewart


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Bob May
Sent: Sunday, February 24, 2008 9:08 AM
To: atm@atmlist.net
Subject: Re: [ATM] subdiameter lap controversies?

The problem is more that going from a hyperboloid down to a
paraboloid often just doesn't happen that way.  Often the outer
zzones go spherical, leaving a hole in the center.  Also you
often end up with a bit of rolled edge to go with that.  If you

--- message truncated ---


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