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pier base option

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#1 mcolbert

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Posted 12 July 2019 - 02:42 AM

most threads on different fora describe steel piers (or wood etc) atop a concrete base.  So I wonder which would reduce vibrations better, the steel pier on a concrete base or a steel pier bolted to a square yard of steel, say about 6-8 inches thick?

 

Thanks

 

Michael



#2 Neptune

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Posted 12 July 2019 - 06:41 AM

I have always had great success with a hole dug about 3 to 4 ft down (depends on frost line) and about 16" diameter and the same concrete above ground is about 12" diameter extending up to your desired height. All one solid piece. 'J' or 'L' bolts sticking out the top. Dampening time from a sold rap to the top section results in about a 1/2 sec dampening time.



#3 mcolbert

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Posted 12 July 2019 - 06:03 PM

Neptune thanks, I have read many threads where people have described their 'adventures' :). in building observatories, piers and bases.  I was wondering more if there would be similar benefits in dampening time if a metal base were to be used and the vibrations travelled horizontally rather than vertically.



#4 izar187

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Posted 14 July 2019 - 01:47 PM

most threads on different fora describe steel piers (or wood etc) atop a concrete base.  So I wonder which would reduce vibrations better, the steel pier on a concrete base or a steel pier bolted to a square yard of steel, say about 6-8 inches thick?

 

Thanks

 

Michael

The 6" base plate will weight over 2000 lbs. The 8" will be almost 3000lbs. 

Even if you have one laying around, and you might, : ) that is one heck of a heat sink sitting under the scope.

Do not know... but suspect steal pier on steal base plate might transmit many vibrations from the base plate into the pier.


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#5 mcolbert

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Posted 14 July 2019 - 05:56 PM

The 6" base plate will weight over 2000 lbs. The 8" will be almost 3000lbs. 

Even if you have one laying around, and you might, : ) that is one heck of a heat sink sitting under the scope.

Do not know... but suspect steal pier on steal base plate might transmit many vibrations from the base plate into the pier.

Izar187 thanks, those are a couple of important points as well! There seems too to be the problem of rust using steel, so I was considering aluminium - that would be slightly lighter.  Whilst it can corrode it seems to be protective to the metal as well.

 

The retention of heat from the day and cool down time should be considered as well - maybe it will take significantly longer for the slab to cool down, especially in summer when we get to 110 degrees +. :). I had planned on there being a timber floor above the slab, but that wouldn't keep the temperature down that much I suppose.  Again more calculations needed.

 

Re the vibrations from plate to pier I will now have to look at testing for vibrations (duration and frequency) from passing vehicles.

 

More food for thought, thanks!


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#6 izar187

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Posted 14 July 2019 - 08:57 PM

Aluminum plate... the cost will be frightening!

Any base plate that large will sweat when it's cold and the air is hot. Aluminum too.

Under a timber floor it will corrode. Even aluminum, and some more so than others, depending on grade/type.

If paired with a steel pier, then there will be electrolysis with the aluminum. If only a little.

Aluminum pier to larger aluminum base plate equals even more cost.

 

I dunno, but I would strongly suggest pouring reenforced concrete, and anchoring the steel pier into that.

All kinds of industrial pier applications have done the figuring on this, for decades.

Even where modest size steel base plates are used, those are bolted onto reenforced concrete.

 

If you need a slab for a base, due to ground conditions or something...

then investigate having a concrete contractor pour you a reenforced concrete slab...

with anchor bolts included right where you need them for the pier.

 

Any experienced concrete contractor will know all kinds of stuff about what goes in for what application.

And after a little planning, likely have the thing finished in a fraction of the time of a hobbyist. 


Edited by izar187, 14 July 2019 - 09:02 PM.


#7 mcolbert

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Posted 15 July 2019 - 02:32 AM

Izar187 thanks for the response, after thinking it over I wonder if this configuration would be acceptable?

 

one piece 90 cms long x 30 cms wide and 10 cms thick (35.5 inches x 11.8 inches x 4 inches)

 

two pieces each 30 cms square (say 12 inches)

 

place in a cross configuration with the N/S blocks attached and secured to the cross beam.

 

placed under decking - allowing air circulation

 

material still to be aluminium

 

possible advantages; lighter, stability for mount/OTA maintained, vibrations still reduced, minimise vibrations from external sources(?), less of a heat sink and being lighter the base could be moved indoors during summer days with 100+ temperatures therefore addressing the sweat problem(?), 

 

 

I know I am going against hard won conventional wisdom here, I'm simply exploring possibilities given other factors such as portability and ease of making several such set ups for different OTAs.

 

Thanks.;)


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