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[ATM] Make a small mirror first
Justin,
You'll make a 6" followed by a 10" much faster and with less total effort
than starting with a 10". This is the voice of experience....
You are going to make lots of mistakes. It is particularly easy to dig a
hole in the center of your mirror when figuring. The only way to fix it is
to remove the huge amount of glass outside of that hole. On a 10" this
will take a long time. If you do the 6" first, you'll make that mistake
and learn from it quickly and avoid it on the 10".
Do a 6" mirror to get the hang of it, then move onto the 10" mirror. Plan
on building the 10" hardware in parallel with the mirror so you'll be able
to star test it - you'll want a halfway decent tube assembly and a good,
stable mount, since star testing is done at high power. While the 10" is
out being aluminized, go back and critically review the 6" and fix it.
Some day later you can build a scope around it.
=Matt
Original Message:
-----------------
From: Justin Morgan Justin.Morgan@watchmark.com
Date: Mon, 18 Oct 2004 21:13:01 -0700
To: gregj888@comcast.net, atm@atmlist.net
Subject: [ATM] RE: best book to learn mirror making?
Hi Greg,
Many thanks for the advice. Unfortunately it looks like the WWU mirror
grinding workshop was cancelled this year (too bad, I would have
attended in a heartbeat).
Everyone is saying that 12-16" is too big for a first mirror, so most
likely I'll start with a 10" mirror. I want to have a mirror that's at
least a little bigger than a C8. :-)
I'll stop by the Seattle Astronomical Society's ATM special interest
group at their next meeting. With their help I'm hoping that the
probability of success will be high(er) given that I'm working on a
large-ish mirror.
Thanks again for the help.
Clear skies,
Justin Morgan
> -----Original Message-----
> From: Greg Jones [mailto:gregj888@comcast.net]
> Sent: Saturday, October 16, 2004 11:17 AM
> To: atm@atmlist.net
> Cc: Justin Morgan
> Subject: Re: best book to learn mirror making?
>
> Justin.
>
> There is an active ATM community in the Pacific NW and a couple of
clubs
> in
> Seattle. A great ATM workshop is held at WWU most years that is worth
> going
> to. Check on the local clubs. They will have hands on help and a
library
> so you can look at several of the books.
>
> As stated earlier, you will get a 16" mirror done much sooner if you
make
> a
> smaller one first. IMHO and 8" f/6 is a great first mirror if you
have a
> little bit of help available. Once done, you'll be able to judge
better
> your next project. We have had 10" and 12" first mirrors successfully
> finished in Portland through our ATM SIG, but there was a lot of
> experienced help and hand holding (one went to the local pro for final
> figuring). If you get in with a club that may be an option.
>
> Mirror making is mostly process: motions, movement, beveling,
cleanliness,
> contact et. al. Very little math, or visible "science." So rather
than
> calculus, it's more like working on a car, sewing or wood working.
That
> is
> to say it takes practice as much or more than studying. The little
thing
> are what get you and when you screw up, the glass breaks. The small
> mirror
> get the chips and dings instead of the large one. We've all been
there,
> so
> nothing specific to you or anyone else.
>
> I have most of the books mentioned. I started with Thompson and like
it
> and
> Howard about as well as any for a first timer.
>
> I have the original ATM 3 book set, chemical stains and all, would not
be
> my
> first choice. The incantations are tough and where do you get
eye-of-newt
> these days...:-). I like the set, but we have better materials
available
> and many suggestions are offered that don't stand up to scrutiny.
Still,
> there are techniques to produce lots of optics/projects an ATM night
be
> interested in. Has anyone tried smelting Al in their back yards?
>
> As a point of reference, I found I had ground through to some bubbles
in a
> 6" f/10 last Sunday. On a small machine and with not much time, it
has
> been
> ground out, will be polished by tomorrow night and figured by next
week
> end.
> I've been working on a 20" f/3.5 for several years... granted with a
lot
> of
> time off. My large machine is under powered, but the 20 mirror took
about
> 110 hours of polishing where a 6" would take 4-6... A 16" f/4 or f/5
is a
> serious project and you'll need the 8" as a finder anyway:-).
>
>
> Greg Jones
> http://home.comcast.net/~dac20/dac_001.htm
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