Re: [ATM] Hello please help me

["Bob May" <bobmay@nethere.com>]

There are a lot of mechanical designs of a telescope on the web.
Most of them are of the Dobsonian design (google for San
Francisco Sidewalk Astronomers) and are probably the easiest
telescope to build.  The optics are Newtonian (parabolic primary
mirror and a flat mirror to bring the light out the side of the
scope) and that design works very well.
The thing here is that the parabolic primary is somewhat easy to
do with the only problem getting the surface properly shaped.
The testing of the mirror is, again easy to do and there is a
fair bit of stuff on the web for how to do the test from the
theroetical by Dave Harbour (I've got a copy of his treatsie on
the subject on my website) to practical by others.  The job isn't
impossible to do but can be fraught with problems for somebody
that doean't have anybody else around to correct some of the
sublte things that can go wrong.
Looking back through the archives of this list will show a number
of people that have worked their mirror through the list and have
answers for a fair number of the problems that have happened and
thier solutions.
Finally, I will say that you can do this as a lot of poeple have
already done it.  I do my grinding at home in my bathroom using a
lazy susan bearing under a big (30Kg) chunck of steel on top of
it and a piece of plywood on top of that to keep the glass from
hitting the hard steel.  I use the lazy susan in place of
rotating the glass just because it is easier for me to push the
block of steel around rather than moving the tool (or mirror)
aroujnd in it's clamps.  In addition, I get to sit down while
doing my grinding and polishing.  Also, a source of water is
readily available in the bathroom which is, as you will find,
quite desirable.  You don't want to have dry glass grit floating
about as large quantities of it tend to give you "miner's
disease" which is a hazard for opticians as it is for miners.  A
short exposure to glass dust won't hurt you but long extended
(years of exposure) will tend to give you the disease if you
don't control the glass dust.  Keeping it wet and flushing it
down the sink and keeping your grinding bench clean all help in
thiis plus the probability of getting a scratch on the mirror is
much lessened with a clean enviroment.
Good luck and find a piece of glass (even ordinary plate glass)
and sstart grinding!
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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