Re: [ATM] ritchey cretians

["Khail Rosenberg" <mikhail.rosenberg@rosenbergtelescopes.com>]

Hi Bob,

I have an ambition to never use machines to make my mirrors, but i think
something for this size, i really will have no choice... I think i will make
a few machines, will help if i want to make something bigger and better..

And i have read about the diamond pads, you are right, even though grit can
be relatively cheap, with such a large mirror i feel i will spend more on
grit than the actual glass itself..

Any advice on machines to actually lift and put it on stands? I do
understand the concern of dropping the mirror, it will make a lot, a looooot
of work really out the window...

Any advice on griding or polishing, and then testing both primary and
secondary will be greatly appreciated.

I believe my course of action will be as follows:

1. Make the 48" glass x 4"
2. make the machines to grind the bad boy... any suggestions on HP for the
motor? 20, should be ok?
3. get three flats made for testing all 48" x .75", i chose this because it
can be made for a pretty darn good price, any comments on the thickness
being too thin?? .75 is ok?
4. ASK ATMLIST.NET where to go from there.. after I already have a ground
out mirror and one thats already polished to a sphear.. where to go from
there??

..... any good step by step plans on the entire process I will be happy to
donate many goodies to a convention, person, school etc...

Thanks,
Mikhail

On 1/18/08, Bob May <rmay@nethere.com> wrote:
>
> Your goals are not that of some little size!  a four foot mirror
> isn't something to just whip together in a few weeks but rather a
> real project of some size.  Nothing you are going to do is going
> to be the same as with a smaller mirror except the sound of the
> mirrors being ground.  You're going to be wanting machines to
> grind and polish the blank just as a start and then machines to
> lift and position the glass on the testing stand.  Don't even
> think of doing any of that work by hand as you'll drop the glass
> at the first opportunity and that will mean a fair bit of money
> out the window.  Even hogging out the glass in the beginning will
> be a fairly major project!  Diamond tooling is the wya to go
> there as you'll be spending that much on grit without any
> trouble, even if you get sandblasting grit for the first few
> grits.
> As to speed, sit down and see what you really need for a primary
> and go from there.  There is generally no need to go to something
> really fast as the performance of a really fast system won't be
> that good and the surfaces will definitely need hand work after
> you're mostly done to perfect the shapes needed.
> Good luck with the project!  Up at Mt. Laguna the large scope is
> a 48" Cassegrain camera and when I was last up there, their
> project was looking at galaxies for novas and supernovas in order
> to gain a better understanding of them.
> Bob May
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