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The Ultimate
Accessory
The Construction of Dunham
Hill Observatory
Mike Lewis - January 2005
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All pictures copyright Mike Lewis
As amateur
astronomers, most folks think we are nuts trudging out in the cold or
bug
ridden night to set-up our scopes. We do this out of our love for the
night
skies. At some point, I think we all dream of a permanent place to
pursue our
passion. With this in mind, I started on a project that
led to what I call “the ultimate accessory”,
a home observatory.
I live in a rural area of Mid-Michigan with skies
that average 5.0-5.2. Not the best, and I also have a light dome from a fairly
large city 30 miles to the east. But, with the addition of a dedicated building,
my observing time has increased 25-30%. However, I would caution
you that this was not an easy project! I spent 2 years in the planning stage
and 2 years of construction. As a matter of fact, I think it will be a work
in progress tweaking and improving.
What ya start with...
One thing I must say
at the outset-check your local and state regulations! This may save
some
heartache down the road. In my situation, without any neighborhood or
association
constraints, any outbuilding under 200 sq/ft did not require a permit
or
inspection, except for the electrical. My decision was to
construct a
12’ x 16’ roll-off structure. (192 sq/ft). I researched
just about all there is to find on the web concerning
home-built observatories and since I am doing all the work myself, this
was the
best fit for me. I also must add that I have worked in the construction
industry 25+ years. I have just under
1.5 acres to work with and picked a spot 125’ from my house. This is
not a
decision to take lightly! Location is
important for obvious reasons. The building consists of a 12’ x 10’
observing
area with a 12’ x 6’ warm-room/lab. The roof of the former rolls over
the lower
roof of the lab.
I decided to go with a permanent pier, so this was
the
beginning. The pier is offset N/S one
foot north and centered E/W on the proposed observing room floor. It is
an 8”
reinforced concrete structure with the bottom “belled-out “ to 20”.
This
enabled me to excavate a smaller area. I made a bolt pattern to
accommodate the
mount I was going to use, bought a “sonotube”™ and mixed the concrete
by
hand. The bolts for the mount are 2’
long embedded in the concrete. The pier itself is reinforced with a
cage of
rebar running the full height and tied to L shaped bars extending into
the
base. It is important to take some time
with this, make sure the form is plumb! When all is said and done, you
will
appreciate this step when polar aligning.
You'd think he'd help...
With the pier
completed, I laid-out the actual structure and pounded stakes at the
corners.
The building was oriented N/S along the long axis. For construction
purposes, I
then off-set the corner stakes 2 feet
in both
directions. There are two schools of thought concerning the floor of
your building,
a wood, deck-like structure or a concrete slab. I opted for a slab. The
wood
type floor is easier to build and a slight bit cheaper but I decided
that
concrete would support the walls well and have considerably less
vibration. I dug out all the topsoil from the building
footprint, anywhere from 6” to 14” in my case, and ordered sand from a
local
contractor. The sand was placed in the hole and compacted. I did this
all by
hand, if you have access to a backhoe, it would be a lot easier. The
floor slab
area was then formed up with 2x4’s and leveled to grade. I also dug an
8” wide
x 12” deep “rat wall” along the exterior of the slab.
At this time, before the concrete pour, I
installed 2 conduits from the base of the pier to the inside of the lab
for cables
from the lab to the scope.
The slab figured out
to be about 2 cu/yds of concrete so a call to a local concrete supply
firm was
made, I did not want to mix that much by hand! The supplier indicated
there was
a 3 cu/yd minimum for delivery, oh well. (ended up fixing some sidewalk
out
front with the extra.) The mud was poured and struck off, I went with a
light
broom finish. After the concrete had hardened a bit, it was covered
with
plastic and kept wet for 5 days to insure proper curing.
The building itself
is traditional 2x4 stud walls, 16” on
center. I went with 6’ high walls and a peaked roof for the observing
area and
a “shed type” roof for the lab. The main roof slides off on 12 hard
rubber
casters ( 6 per side/3” diameter ) inside aluminum tracks over the lab
roof and
supported by 4x4’s place in concrete, 4’ below ground. The tracks and
wheels
can be purchased online, a google search turns up a myriad of suppliers
with
items to meet your individual needs. I found a local supplier, Grainger
™ who can also provide these items
nationally. If I were to do this over, I
would pay the extra and use “inverted” V tracks and a larger diameter
grooved
wheel. The roof over the lab is regular shingles and the larger one is
metal. I
went this route to minimize the weight of the one that has to move, its
pretty
heavy, but doable by hand. The roof of the lab area is 2” shorter to
allow the
movement of the larger one. At some point I may install a roof removal
system.
All that was left for the basic structure was siding. I chose a regular
wood
siding in 4’x8’ sheets. Vinyl would be another option. The siding was
painted
to match my house. Well, fall 2003, the inside of the lab was not done,
but I
enjoyed a winter of observing out of the wind in my unfinished
observatory.
The next year was
the fun part of the construction! I dug a trench from the house to the
observatory to bury the electrical and phone cables. It is important to
separate these two wires, the power supply may adversely affect data
transfer,
(wireless is another option). I was lucky in the fact that the previous
owner
had had a hot tub and an unused breaker box was already located in the
breeze-way. I ran 10-3 underground (direct bury) wire from the box to
another
one in the observatory. Installing the wire in a conduit is another way
to go.
I then ran direct bury phone cable in a separate trench. In hindsight,
I should
have planned better, cat-5 or wireless would have been a better
solution. I
purchased two books on wiring and accessed the national wiring code
online to
help with the actual wiring of the building. I then asked the help of a
friend
who is in the electrical business to take a look at my work. He
indicated a few
mistakes and we made the corrections, the electrical inspection went
well and I
only had to make one minor change. One point, be sure and ground the
system at
the building and be generous with plugs!
Now, the only thing
left was to finish the interior of the lab. I insulated the walls and
ceiling
of only the lab and used 3/16” wood paneling. I built a desk and put up some
light fixtures. A 3’ electric baseboard heater keeps it toasty. I have
one
access door on the south side of the building and an interior door
between the
two rooms. I also have a window between the two. <>
Now the bottom line-
how much did it cost and does it work! My total investment is at
$2300.00. I
was trying to keep the cost around two grand, so, I’m close to
projected. Also,
keep in mind I did ALL the work myself.
OK, does it work? Absolutely!!!
It’s not perfect by any means and I will continue to tweak. Was it a
ton of
work? You bet! But, once you personalize
with desk, shelves, storage, lighting, music and all the other stuff we
haul
around, it is a joy to use!
My observatory now houses a Meade LX50 7”
Maksutov-Cassegrain with a Borg 76mm ED riding on top. I also have an
8”
Homemade DOB and a 120mm achromat. On any given night, I can be at the
eyepiece
in 10 minutes max!! The scopes are all at or close to ambient
temperature so a
1 hr sky tour on a work night or a short notice session is a breeze. If you are contemplating any type of
permanent observing structure, go for it! You will not regret it. My
observatory truly is the “Ultimate Accessory”.
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