Re: [APML]: pier construction

["Bob Freeze" <rfreeze@usit.net>]

I poured an 8" (yes, undersized) concrete pier "as one" with a 3ft
deep by 3ft diameter base for my 12".  The pier has ZERO ring and is
SOLID.  The only vibrations I experience are from the forks - this
only if I twap the 'scope.  These vibrations disappear in 3 to 4
seconds.

I placed all-thread into the top of the sonotube/concrete to match the
superwedge bolt pattern with washers resting in the top of the
concrete.  A plywood template was used for this.

The only thing I don't like about the 8" diameter is that I had to
bolt a piece of steel on the side for the azimuth adjuster.

All in all it works perfectly.


Bob

-----Original Message-----
From: Robert Reeves <rreeves@connecti.com>
To: astro-photo@nightsky.com <astro-photo@nightsky.com>
Date: Thursday, February 12, 1998 12:03 AM
Subject: Re: [APML]: pier construction


>
>At 07:05 AM 2/11/98 -0800, you wrote:
>>
>>You could use a sono tube. Fill it with concrete. Pour it as one
with
>>your slab, and when you get ready to make a larger one slide the
>>tube(8") over the top of the smaller one, bolting it down with the
bolts
>>you didn't forget to put in the slab when you poured it. I suspect
they
>>are using the bolts (in the picture) to level the tube. Why not just
>>pour the 8" ?
>>--
>>Greg Mueller
>>Amateur Astronomer, Machinist, Filmnut
>
>Perhaps not such a good idea.  A solid concrete pier will ring like a
bell
>if vibrations are introduced.  A rule of thumb is have a pier of
equal
>diameter to the aperture of the instrument going atop it.  A steel
pipe is
>good and even better when filled with coarse loose sand.  The sand
damps any
>vibrations.  The pier should be anchored in the ground separately
from the
>observatory building or footsteps, moving the dome, etc., will make
the
>image jiggle.  I have an 8-inch sand filled pipe under my Schmidt
camera.
>It is anchored to a concrete block cast separately from the building
slab.
>It has worked great since 1986.
>
>Robert Reeves                Home page
http://www.connecti.com/~rreeves
>520 Rittiman Rd.             Email     rreeves@connecti.com
>San Antonio, Texas  78209    Phone     210-828-9036
>                             Location 29.484N  98.440W  200 meters
>
>