Greetings and Salutations...

On Tue, 4 Nov 2003 18:24:39 +0000 (UTC), domain
(qedude) wrote:

I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten

good suggestions in the other posts to this question.
How "low" is the vibration you are seeing and how close
is the highway?
It may be that the only way to fix this problem is to
decouple the telescope from the ground movement. For example,
you could pull the support shaft loose, & cast a large weight of
concrete around it (say...300 lbs). Be sure to put four lifting
rings on the upper surface of the concrete block, near the
corners. Then...build a heavy frame mounted on the original
pad. Make it a few inches larger than the block on the
shaft...say..maybe 3-5" per side. USe some heavy springs to
support the block base for the telescope inside the frame, so
it is free-floating. If necessary, you can get some cheap
Lawn Tractor inner tubes from Northern Tool, or some other
place, and, put them between the block and the frame, to
add some additional damping. It is best that they only
be inflated to a couple of PSI, though.
If your problem is low frequency vibrations from
the highway, this should do it. Oh...it occurs to me
it should be pretty easy to see if this is the problem,
though, as it should vary depending on traffic...
Regards
Dave Mundt