Re: Steel Pier recommendations


ROBERT WYNNE
 

Can this resonance be baffled by adding strapped turnbuckles? -Best, Robert

On 05/26/2021 2:54 PM Don W <westergren@...> wrote:
 
 
Ringing (like a bell) is never a problem - it is a high frequency / low amplitude motion that never is seen by the scope.  Ringing is started with a bang, which you will be VERY unlikely to do.  You don't hit your pier with a hammer do you?

Stiffness of a pier is very important if you are visual observing and want to manually focus on Jupiter - just touching the focus knob can move the object and set up fundamental oscillations (primarily of a cantilevered pier - mounted on concrete).  A tripod or AstroPhysics portable pier with a wide doesn't have this problem.  But a metal pier bolted or inserted into concrete is a spring ready to wave back and forth.  Putting anything inside a tube (sand or concrete) is a disaster waiting to happen - adding mass to the spring and causing a very long oscillation lasting for seconds.

If the pier is used only for imaging, these concerns for oscillation are much less a problem, since only wind is likely to affect the bending of a tubular pier.  For these type piers, the difference in stiffness between aluminum and steel is 3:1.  The modulus of aluminum is 1/3 that of steel, meaning the aluminum is far worse.

Don

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