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Pack sand?

Started by NebSteve, 10/04/2010 07:47AM
Posted 10/04/2010 07:47AM | Edited 10/04/2010 07:48AM Opening Post
Hi All,
For a pier, I use an old steam pipe with huge flanges bolted to a concrete foundation burried deep under the floor of my dome and isolated from it. I've gone to great lengths to reduce any vibration on the scope.

The pipe had been filled with sand, but this didn't damped vibration very quickly. If you slap the side of an empty pipe (and who doesn't from time to time) you get a nice musical note like a bell ringing. That's certainly not what you need for a mount for a telescope. Without sand the ring or echo would go on till it was undetectable at about six seconds. With the pipe filled with sand it dampened out after two seconds. I'm trying to beat that.

The sand was a mix of course sand off the ground with fine sand form the nearby Home Depot. I've decided to try a mix of sand, vermiculite and shredded rubber. First I must get all the sand out of the pipe.

Did you know using a Shop-Vac to remove sand causes a really exciting static electric buildup?! Wow... There's still about two feet of sand in the pipe, but I'll get there.

Anyway I will keep you all posted on the unofficial vibration dampening properties of the new mix.
Thanks,
Steve
8)
Posted 10/04/2010 10:17AM #1
HI Steve,
I have heard that adding oil to the sand helps, but I have not tried it myself.
Also, I do know they use foam in truck frames to lessen vibration. It might also be a good idea, you know the spray in type that expands. But if you were not satisfied it would be tough to remove.
I have also heard of concrete being used, certainly would add mass. grin

[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 10/05/2010 11:08AM #2
Steve Hollenbach said:
...... If you slap the side of an empty pipe (and who doesn't from time to time) you get a nice musical note like a bell ringing. That's certainly not what you need for a mount for a telescope.....

Why not?
When using your mount do you hit the pier hard enough to make it ring?
Does the wind blow hard enough to make pier ring and sing?
I know there are people who go to great lengths to make their piers stop ringing, but why? Of course any metallic cylinder will have a resonant frequency, but does this ever affect the stability of a pier? Has anyone ever had an image ruined by a resonating pier?
At the risk of saying the emperor has no clothes, I will answer "No".
If you want to make a stable pier, the most important things are the diameter of the pier, the presence of gussets, and a solid connection to an immovable mass in the ground.
It sure seems like getting into a tither about a pier ringing when you hit it with a hammer is a solution in search of a problem.
Of course any man should be free to choose his goals, I just think that you're tilting at windmills with this one.

dan