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[ATM] Re: 40" mirror
Yup Ken, everything you mention is correct but us scope makers have these
urges to try other things and I suspect Jerry is wanting to explore and
learn the processes needed to create a large scope, even making the blank!
I'm quite interested to see how it all goes.
Keep us posted, Jerry.
Mike Conron
Ken Hunter writes:
> Jerry...
>
> Before you indulge your illness (aperture fever),
> please take a moment to analyze what you are getting
> into IF YOU SUCCEED. Mounting a 40 inch piece of glass
> is going to be a Herculean task (even if you make the
> cell out of plywood and AstroTurf), the cost of
> aluminizing a 40 inch mirror is bound to be well over
> $1500.00 plus shipping, and the number of places that
> can do this work is fewer than you might imagine so
> you likely won't get an ATM discount. Hell... Just the
> cost of a 20 foot stepladder these days is outrageous
> and you're gonna need 2 to put it together. (I know
> you already have them from your business) ;0)
>
> You mentioned earlier a figure for THE weight of the
> glass. I don't remember what you figured it to be but,
> it seemed awful low at the time. I think my 26.5 inch
> X 1-5/8 inch blank weighs more than you quoted for
> your proposed 40 inch disk.
>
> I'm not trying to inhibit or discourage you in any
> way, just suggesting that you consider the
> possibilities of what you are in for once you have a
> 40 inch blank. I was offered a 1 meter cast blank (at
> no cost) by Lynn Hepburn shortly before he passed away
> and wanted it to work out but after figuring out the
> amount of work and finances needed to put it into
> service, I declined the offer and took the glass I cut
> the 26.5 inch blank out of instead.
>
> Good luck! For one man it's a lifetime committment.
>
> Ken Hunter
>
> ps...
>
> Today I received a quote for a 2 foot square of clear
> plate glass 3/8 inch thick to be used for a
> Schmidt-Cass corrector. Over $100.00 plus tax, plus
> shipping and this did NOT include any kind of
> guarantee that the glass was annealed to a usable
> amount of stress or usable for ANY purpose. I cannot
> even order the glass and refuse it if the stress test
> is not good. Spend your money, take your chances. I'm
> hoping to find someone with the glass in stock that
> will let me test it on the rack before I purchase it.
>
> Wish me luck!
>
>
>
>
> --- "Jerry B. Hillman" <JBHillman@ev1.net> wrote:
>
>> Hello everyone,
>>
>> Since I am going to invest a good deal of money and
>> a considerable amount of
>> time in the venture of melting the glass and casting
>> a 40" mirror, I would
>> like to hear anyones input about very large mirrors.
>> I am interested in hearing about F ratios compared
>> to useability and
>> difficulty in manufacture. I don't want to invest a
>> lot of time making an
>> F2 only to find out that uncorrectable coma is the
>> inevitable result.
>> Don't misunderstand me. I have no idea if an F2
>> would have uncorrectable
>> coma. I just pulled an example out of my hat to
>> help explain what I need.
>> The first piece of glass I am going to cast is for
>> the secondary. I need to
>> know what the F ratio of the telescope is going to
>> be before I take that
>> step so that the glass will be large enough. I know
>> that starting with the
>> secondary is sort of putting the cart before the
>> horse, but casting and
>> annealing the secondary will tell me if my methods
>> are feasible for a larger
>> mirror.
>> Clear skies, Jerry
>>
>> _______________________________________________
>> ATM mailing list http://www.atmlist.net/
>>
>
>
>
>
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Mike Conron
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