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Pier Question

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#1 James Ball

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Posted 11 July 2020 - 07:57 AM

I image from my deck which is about 5 feet above the ground.  When I built the deck I left an opening in the floor for a pier, currently I have a 4x4 treated post there just stuck in the ground as a test setup.  It works good for the iEXOS100 mount and ETX90 and even the 150MCT I use, but it isn't tall enough to comfortably use the AT102ED as near zenith I have to almost lie on the deck to be eye level with the eyepiece.  I am trying to decide if I want a longer post set in concrete or a steel post bolted to the top of a concrete foundation.

 

Here is my current setup, the wood post would just be taller.

 

iEXOS100 And ETX2

 

I am looking at this as a steel post

 

https://www.lowes.co...Post/1000205861

 

I could remove the jack part and put on some type of solid adapter for the mount.

 

I just wonder which would damp vibrations better, the solid wood or the hollow steel?

 

To keep the wood straight I have a box that wedges between the post and the opening in the deck that fits snugly and can be lifted up during imaging to isolate the post from the deck.  If using the steel post, should it be filled with sand to help reduce vibrations?



#2 Couder

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Posted 11 July 2020 - 08:35 AM

The jack posts are only 3" OD. In my opinion, you would be better off to remove the wood post and put in a taller one. Now that you have the hole dug, I'd probably 1) dig it deeper and/or 2) concrete it in.



#3 James Ball

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Posted 11 July 2020 - 09:32 AM

The jack posts are only 3" OD. In my opinion, you would be better off to remove the wood post and put in a taller one. Now that you have the hole dug, I'd probably 1) dig it deeper and/or 2) concrete it in.

I definitely plan on putting concrete there.  I was leaning towards the wood post but wanted another opinion, thanks for responding.  Another advantage I see with the wood is I can buy it 10ft long and adjust to any length I need and if it does happen to bend over time I can correct that by taking a half inch or so off the top to level it up again.

 

I think the steel would have a tendency to "ring" while the wood should dampen that out quickly.



#4 *skyguy*

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Posted 11 July 2020 - 11:20 AM

Twenty years ago, I built a 13' pier using concrete 16"x16"x16" chimney blocks for my garage-top observatory. The pier was left hollow ... no concrete fill ... and it cost me $75 for materials. This pier has far exceeded my performance expectations for strength and stability.

 

OrbitJet Observatory:

 

https://www.flickr.c...57644177074161/

 

I would suggest you build your 8' pier using 8"x8"x8" concrete blocks:

 

https://www.lowes.co...-7-5-in/3368592

 

The cost would be about $14 for the blocks and adding in the cost for a couple bags of mortar. You could fill it with concrete of leave it hollow. It's an easy DIY project and there are plenty of "block laying" tutorials on YouTube.

 

Here's a CN topic on "wooden pier vs concrete"

 

https://www.cloudyni...er-vs-concrete/

 

... and one on concrete block pier construction:

 

https://www.cloudyni...l= block pier*

 

I have posts in both topics.

 

Good Luck with your pier build .....

 


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#5 James Ball

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Posted 11 July 2020 - 12:45 PM

Twenty years ago, I built a 13' pier using concrete 16"x16"x16" chimney blocks for my garage-top observatory. The pier was left hollow ... no concrete fill ... and it cost me $75 for materials. This pier has far exceeded my performance expectations for strength and stability.

 

OrbitJet Observatory:

 

https://www.flickr.c...57644177074161/

 

I would suggest you build your 8' pier using 8"x8"x8" concrete blocks:

 

https://www.lowes.co...-7-5-in/3368592

 

The cost would be about $14 for the blocks and adding in the cost for a couple bags of mortar. You could fill it with concrete of leave it hollow. It's an easy DIY project and there are plenty of "block laying" tutorials on YouTube.

 

Here's a CN topic on "wooden pier vs concrete"

 

https://www.cloudyni...er-vs-concrete/

 

... and one on concrete block pier construction:

 

https://www.cloudyni...l= block pier*

 

I have posts in both topics.

 

Good Luck with your pier build .....

That is a very nice observatory!  I have had something like that in my head for when I am able to build a garage later on.  For that size the concrete would definitely be better than the cost of a steel pipe that long.

 

If I go much larger than 6" now I will have to get under the deck and make the opening larger.  The opening now is roughly 7"x7".  I guess a 6"x6" post would work.  The total weight of mount and scopes is barely 25 pounds so shouldn't need the large 4 square bolted posts pier.  Also I take the mount in each night and am only doing some planetary imaging.  Just the upgrade from 4" to 6" post set in concrete would be a vast improvement I think.  Plus if I ever sell the house or build the roll off on a garage I just need a chainsaw to remove the post in the deck.




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