From: "Frank Q" 
To: "Kenneth L. Hunter" , 
Reply-To: "Frank Q" 


Hi All

Given the following:

Spherometer diam = 3.5", this gives radius r = 1.75" Radius of
Curv (8" F/8; FL = 64") R = 128"

Use our old friend s = r^2 / 2R ...... gives:   s = (1.75)^2 / 2x128 = 0.01196"

What could be simpler ??

Cheers
Frank Q



----- Original Message -----
From: "Kenneth L. Hunter" 
To: 
Sent: Thursday, July 24, 2003 2:08 PM Subject: Re: ATM Mirror Grinder pictures


>
> An easier way to do this would be to download my spherometer spreadsheet
from:
>
> http://groups.yahoo.com/group/atm_free/files/Sphero/
>
> Get the Sphero.zip file, unzip it, and from there it's easy!
>
> Ken Hunter
>
>
>
> "Dwight K. Elvey" wrote:
>
> > Hi
> >  I don't think your calculations are correct? For an
> > 8" F8, my calculations say that a 3.5" diameter spherometer
> > should read a little shy of .012". Here is my calculations:
> >
> >  8" f8 has a focal length of 8" * 8 = 64". This
> > is a ROC of 2 * 64" = 128"
> >
> > Using right triangles and 3.5" I get the equation:
> >
> > (128 - x)^2 + (3.5/2)^2 = 128^2
> >
> > This expands to:
> >
> > x^2 - 256*x + 3.0625 = 0
> >
> > I used one one of the net quadratic equation calculators to
> > get:
> >
> >  x = 0.01196
> >
> > See:
> >
> > http://www.math.com/students/calculators/source/quadratic.htm
> >
> > or use:
> >
> >  x= ( -b +- sqroot(b^2-4ac) ) / 2a
> >
> >  on your own calculator.
> >
> > Later
> > Dwight
> >
> > >From: "James P Crombie" 
> > >
> > >The .006" was with the 3.5" spherometer, if you
calculate it out it
> > >translate to about .048" across the 8" of the
mirror.  So I have
another
> > >.002" to go for an f8
> > >
> > >Frank Q wrote:
> > >
> > >>Hi All
> > >>
> > >>An excellent effort.
> > >>
> > >>I have a question -- My recollections of grinding an
8" f/5 is that
> > >>I could excavate much more than 0.006" in a few hours - does
> > >>anybody else find this or is my memory rapidly failing?
> > >>
> > >>(I used 80 grit and a full sized plate glass tool)
> > >>
> > >>Cheers
> > >>Frank Q
> > >>
> > >>----- Original Message -----
> > >>From: "James P Crombie" 
> > >>To: "Atm List" 
> > >>Sent: Wednesday, July 23, 2003 3:38 PM
> > >>Subject: ATM Mirror Grinder pictures
> > >>
> > >>
> > >>
> > >>
> > >>>Hello all
> > >>>I did another couple of hours with the mirror
grinding machine and
got
> > >>>the sagita to .006"(this is with a 3.5"
spherometer not overall ) or
a
> > >>>ROC of  166" .   I thought I would start with
something easy like an
8"/f8
> > >>>
> > >>>http://www.jamescrombie.com/temp/closeupmirror1.jpg
> > >>>http://www.jamescrombie.com/temp/wideview1.jpg
> > >>>http://www.jamescrombie.com/temp/mirrorgrinder1.avi  
 (note 1.7mg)
> > >>>http://www.jamescrombie.com/temp/mirrorgrinder2.gif  
  (same as
above
> > >>>but will open in browser window)
> > >>>
> > >>>--
> >
>>>-------------------------------------------------------------------------
-
> > >>>
> > >>>James P Crombie
> > >>>
> > >>>Summerside      Machinist
> > >>>Prince Edward Island      Amateur Astronomer
> > >>>Canada      3D Designer
> > >>>
> > >>>E-mail      jpcrombie{at}pei.eastlink.ca
> > >>>Astronomy webpage      http://www.jamescrombie.com
> > >>>Rhinoceros 3D webpage      http://www.jamescrombie.com/rhino/
> > >>>Mirror Grinder page          http://www.jamescrombie.com/pics/
> >
>>>-------------------------------------------------------------------------
-
> > >>>
> > >>>
> > >>>
> > >>>
> > >>
> > >>
> > >>
> > >>
> > >
> > >--
> >
>--------------------------------------------------------------------------
> > >
> > >James P Crombie
> > >
> > >Summerside                  Machinist
> > >Prince Edward Island        Amateur Astronomer
> > >Canada                      3D Designer
> > >
> > >E-mail                      jpcrombie{at}pei.eastlink.ca
> > >Astronomy webpage           http://www.jamescrombie.com
> > >Rhinoceros 3D webpage       http://www.jamescrombie.com/rhino/
> > >Mirror Grinder page          http://www.jamescrombie.com/pics/
> >
>--------------------------------------------------------------------------
> > >
> > >
> > >
> > >
>

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