Re: [APML]: ATM question

[Wil Milan <wmilan@airdigital.com>]

Jim Fedina wrote:

> The tube is probably the thing I would like to know from everyone.
> What have you used for tubes? I can't think of anything that I have seen
> that could be used. I know you can probably buy a tube from a supply
> house, but I figure that might be more expensive than something that is
> used for an entirely different purpose.

I've used aluminum irrigation tubing, available in .064" and .084" wall
thicknesses. The thinner tubing works well up to 8" diameter tubes, for
larger tubes I'd go with the .084". The cost for irrigation tubing is very
low; I recently bought an 8" x 60" tube for $24 brand new and cut to exact
length. It's mild aluminum and very easy to machine.

Irrigation tubing is available from agricultural supply centers which
specialize in irrigation equipment. If you can't find such a place in your
area try Rain For Rent in Chandler, Arizona; that's where I get mine.

The other place you might shop for aluminum tubing is a scrap metal dealer
where you can buy it by the pound. Unless you have a lot of money you do
*not* want to buy new structural aluminum tubing from a regular metal
dealer; it'll certainly be good tubing but new structural aluminum is very
expensive.

> Also, roughly how much would the primary mirror for an 8inch cost?

Figure $250 - $300, give or take for quality, material, and other factors.
That's for a ready-to-install mirror.

> Is there two prices, one for the mirror ready to install and one for
> grounding it down yourself?

Absolutely. A plain glass blank ready to grind is *much* cheaper than a
finished mirror ready to install, the difference being the price of the
labor and the cost of aluminizing the mirror.

> I assume the ready to install would be more
> expensive but easier on a newbie.

Right on the money on both counts. Grinding mirrors is interesting and
rewarding to some (not me), but it requires tools and skills which have
nothing to do with any other aspects of telescope-making. You certainly do
not have to make your own mirrors in order to make your own telescope; the
two are really quite separate and distinct interests and skills.

Wil M.
--
"When I consider your heavens, the work of your fingers,
the moon and the stars which You have set in place,
what is Man that you are mindful of him,
or the son of Man that you care for him?"  -- Psalm 8