Re: (ATM) PIER QUESTION

Steve Strickland (lensnut@tpoint.net)
Sat, 26 Aug 1995 02:18:28 -0500

>Help! I'm building an observatory in my back pasture and I need some advise.
>My problem started with the pier that holds my C8. Following the design in my
>scope manual, I buried a six foot x 4" diameter schedule 80 pipe three foot
>into the ground. About 350 lbs of concrete was poured around the pier and
>inside the pipe. On top of the pipe I welded a flange that holds my
>fabricated
>wedge. This wedge consists of a piece of 8" long x 2 1/2" diameter pipe cut
>and re-welded at about 45 degrees (my latitude). On top of this I put a 1/4"
>aluminum disk that has the appropriate bolt hole pattern matching my scope
>base. Once assembled, I immediately noticed a horrible vibration problem. In
>looking back at the design, the scope is placed off the pier axis quite some
>distance, thereby creating a long lever arm. The next night I chucked the
>custom wedge and bolted a Celestron wedge on top of the pier. This wedge
>reduces the lever arm problem greatly. The vibration was somewhat less, but
>is
>worse than the field tripod, wedge, scope combo! The vibration is bad enought
>that it is hard to focus the scope. What gives? BTW I was using a 18 mm
>eyepiece, barlow, and using Jupiter as the target. My goal of the pier is to
>allow long exposure photography. My thoughts at this point are 1) put three
>guy wires on the pier at 120 degree intervals, thereby placing the pier under
>tension, 2) pour more concrete around pier, 3) yanking the damn thing out of
>the ground with a very large tractor and start over with a better design.
>Please let me know what your thoughts are.
>
>Thanks in Advance
>
>Norm Anheier (nc_anheier@pnl.gov)

Sounds like maybe a slab foundation to me, or built on rock?

Vibration from the observatory floor must be isolated. Slabs will not work. Neither will building on rock. There are solutions, but you may need to post more detailed information. The pier itself will not vibrate, no matter the degree of cantilevering, without an external source of energy. You moving around is the most likely source of that energy. How is it getting transmitted to the pier? Let me know, I'll be happy to share my experience.

Steve Strickland Lensnut@tpoint.net