From: "Frank Q" 
To: "scottythefiddler" ,
        "ATM Group" 
Reply-To: "Frank Q" 


Hi All

Good one Scott ........

Making flats is no worse than making mirrors...

There are some aspects that make it a bit easier than mirrors:

* There's no hogging out
* You can start with 400 grit
    === Grinding is heaps faster
* But figuring is just as bad (good??) as a mirror

* If you just want an optical flat, you've finished!! you don't have to coat
it = no further expense.
Then you can use it to test other bits of window glass to see if they can
be pressed into service
without any figuring !!!

* In my part of the world, you're better off making one rather than buying
one !!!

Cheers

Frank Q



----- Original Message -----
From: "scottythefiddler" 
To: "ATM Group" 
Sent: Wednesday, March 05, 2003 3:24 PM Subject: Re: ATM Flats


>
> ----- Original Message -----
> From: "Bob Walker" 
> To: "ATM Group" 
> Sent: Tuesday, March 04, 2003 10:55 PM
> Subject: ATM Flats
>
>
> >
> > I'm baffled.  Is making flats really that hard?
>
> Hope your scope is baffled, too......  :O)
>
> Try it, you'll like it.  Just finished figuring two small diagonals today
> with some offlist advice from one of the list members.  I won't mention
his
> name so as to prevent him from being deluged with correspondence, but I
hope
> he will step forward, and take a well deserved bow.  It is a wonderful
> feeling to complete this stage of production, and I can barely express my
> gratitude for his help.
>
> I can't really say how hard it is to make a large flat, as mine are good
for
> about a 1.5" minor axis.  There are two of us making 3 flats using the ABC
> method.  My friends flat is the best of the bunch, at about 16th wave.  He
> finished it about 2 months ago, but we were unsure as to how good it
> actually was, until I was able to get the other flats in the same
> neighbourhood, .  What is most gratifying is that my ATM partner is nearly
> blind, and he did it with very little help.  Basicly, I have been his eyes
> when he needed help, reading fringes, etc.  He does have vision, but is
> extremely shortsighted.  When he puts his eye to the eyepiece, he can
focus
> for any shortcomings in his sight, and it is one of the few opportunities
> for him to see as most others do!
>
> I am working on an 8" test flat, which is a few waves from flat.  It is
> improving steadily, but slowly.  There are a few of us who are going to do
> some 8" paraboloidal mirrors soon, so I will test it and hopefully finish
it
> when someone gets a good sphere with a smooth surface.  My guess it that
it
> will be a little easier than making a same size paraboloid.   Somehow, it
> seems to be easier to concentrate the figuring action where it is needed.
> If the flat is a little convex, it is easy to work at the edge of the lap
to
> make the lap a little convex, to counteract the figure.  The same is true
> for the center of the lap with a concave flat.  Intuition seems to work
with
> a flat, but it may not get you far with a parabola.  Ask me again after
the
> flat is finished, and you might get a different response.
>
> We plan to do a fair number of flats for our own use.  The small ones were
> an experiment to see if we could do it, and the experiment has been
> successful so far, but we are not 'out of the woods yet', as we need to
cut
> the ellipses out of the 3-1/4" discs that we have.  The small flats are a
> fair bit of work.  We did them for the experience and the enjoyment,
rather
> than trying to save a few bucks.  Ultimately, we hope to save some money
> when we start building the larger scopes, such as a 14" binoscope.  Even
> then, the large diagonals won't be too large, likely around 3.5"
to 4" on
> the minor axis.
>
> Go for it,
> Scott Donaldson
>
>
>
>  I've seen a lot of
> > correspondence between ATM's looking for flats of various sizes, and
I've
> > seen what some of them cost.  Granted, it doesn't make much sense to
make
> > your own 1.8" diagonal when you can buy one for $15, but
what about the
> > larger ones?  Can figuring a 1/10 wave flat a few inches across be any
> > harder than figuring a 6"  (or 16" or 26"!) sphere
or paraboloid?
> Texereau
> > shows how to make a flat; doesn't look too tough.  Am I missing
somethig,
> or
> > is making flats just considered  Boring?
> >
> >  *  Best regards, Bob
> > *
> >          *           *   *
> >
> >             *         *
> >
> >
> >
>
>

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