Click on images for full size...
This pier was the third attempt at a stable platform for visual and photographic
observing inside Stone Haven Observatory. The rather massive, rectangular base
you see is 3'W x 2'D x 1'H and weighs ~300lbs. It was fitted with 4 bolts epoxied
into holes formed while the cement was curing.
The first attempt at a pier was a 6" diameter 1/8" walled steel pipe, filled
with sand, that was bolted to the base. Heavy accoustic rubber and washers were
installed between the pier and base to reduce oscillations. The wedge that appears
on the current pier was attached to the top. The vibrations of this pier were
horrific at best, even after filling the pipe with sand and fashioning some
"flying gussets" of rope from the wedge to the base. These gussets reduced,
but did not eliminate low frequency oscillations on the order of 1-20 Hz that
would last for at least 10 seconds.
The second attempt was with sonotube of 8" diameter, to be filled with concrete.
In an attempt to pre-second guess myself, I placed a sheet of heavy plastic
between the sonotube and the original base, just in case something went wrong.
Heavy construction "straps" were used to attach the concrete pier, via the bolts
onto the base. After filling the form, 2 pieces of rebar were installed through
the sonotube to provide a platform for a shelf of some sort for ep's etc. After
the concrete cured, the rebar shelf supports had sagged over night. While attempting
to bend and straighten them, the whole shebang came loose from the base, bending
the straps and rendering the new pier useless. Thank goodness the scope wasn't
on it!
This final attempt is basically the same as the second attempt, with the exception
that it works! I had to bite the bullet, and attach the whole kit and kaboodle
to the bolts on the base. I used a 12" diameter sonotub and more straps to accomplish
this part. I suppose I could have continued this size up to the wedge, but decided
to change to an 8" tube, 12" off the ground. I offset the upper portion toward
the South side of the observatory, in order to move the ep side of the scope
away from the North wall a bit. The upper portion has 2 pieces of 1/2" rebar
criss-crossed, extending up to within 3" of the top. The straps at the bottom
are secured with heavy nuts, lockwashers and a flat washer. At the top is a
hole with a bolt epoxied in place in the same manner as the base bolts. This
is called the "Epoxy-tie" system by the manufacturers. The bolt then passes
through a hole in the center of the wedge, giving adjustability in Azimuth for
polar alignment.
Front view. The logo and runes were written by my daughter, Robin. You can just see one of the straps that holds it down sticking out on the lower right.