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Wooden Pier ?

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#1 Berny

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Posted 23 February 2021 - 10:05 AM

Has anybody ever thought of, or experimented with using wood to construct a pier?  Lots of pro's and cons, I know.  But would it be practical?



#2 bridgman

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Posted 23 February 2021 - 10:15 AM

It has been done quite a few times and seems to work well. The primary application seems to be "semi-permanent" where someone wants a pier but isn't sure the location will be close enough to permanent to justify putting something in that has to be taken out with a jack-hammer or excavator.


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#3 ram812

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Posted 23 February 2021 - 10:43 AM

Good morning! You may want to check out CN's "Observitory" forum and look up "Pier Engineering" and other various threads about pier building. Awesome minds contribute there and as noted, several folks have done just what you're looking into. Good luck!
Ralph
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#4 michael8554

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Posted 23 February 2021 - 11:57 AM

5 years ago I made mine from four 4"x4" posts glued and screwed together to make an 8" x 8" post

 

I checked the end-grains and offset them to limit any movement due to damp.

 

The end in the ground was painted with bitumen to waterproof it.

 

The end rests on a brick, and the hole is filled with pea shingle.

 

Happily guiding at 1280mm FL.


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#5 macdonjh

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Posted 23 February 2021 - 05:45 PM

Good morning! You may want to check out CN's "Observitory" forum and look up "Pier Engineering" and other various threads about pier building. Awesome minds contribute there and as noted, several folks have done just what you're looking into. Good luck!
Ralph

In addition, there is a thread specific to wood piers in the Observatory forum as well.  speedster and others from the "pier engineering" forum participated there as well.  As bridgman and michael8554 say, several have done it successfully.

 

The reason I didn't was my concern a wood pier wouldn't be stable enough to hold polar alignment for years at a time.  I'm sure michael8554 gets no less than several weeks of good photography before he feels the need to adjust he polar alignment.  I just wanted to do what I could to be able to forget all about that for years at a time.  I didn't consider tweaking polar alignment for nearly five years after I built my concrete pier.  Of course, when I replaced my mount I had no choice. smile.gif


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#6 ram812

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Posted 23 February 2021 - 06:28 PM

Yes, indeed! I read pretty much that thread start to finish, and every other pier related material and came to the conclusion a concrete filled tube was the only solution for me, I thought polar alignment stability was also the #1 reason for not choosing wood. That being said, what about a 10" diameter seasoned, solid white oak post 8 or 10' deep? I have a few laying around and am exploring a backyard extra pier for my Alt.-Az. quicky set up?😁. Just a thought...
CS, Ralph 😉

#7 macdonjh

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Posted 23 February 2021 - 10:42 PM

Yes, indeed! I read pretty much that thread start to finish, and every other pier related material and came to the conclusion a concrete filled tube was the only solution for me, I thought polar alignment stability was also the #1 reason for not choosing wood. That being said, what about a 10" diameter seasoned, solid white oak post 8 or 10' deep? I have a few laying around and am exploring a backyard extra pier for my Alt.-Az. quicky set up?. Just a thought...
CS, Ralph

Eight feet deep may be overkill- it depends on your soil conditions.  However, if you can go that deep without a lot of extra effort, there is no harm in it.  I had actually planned to go down nine feet with my pier.  When I used the auger I found three feet of sand, three feet of clay, then sand again.  When I hit that second layer of sand I quit drilling.  So my pier is approximately seven feet below grade, forty-two inches above grade.  As I said, polar alignment was stable for five years, then I changed mounts.  Clock started over in October 2019.

 

The seasoned oak will definitely be more stable than treated wood will initially be.  It will move, though, as it gets wet and subsequently dries out and wets again.  I have no idea if it will move enough to make you want to tweak polar alignment.  I'm not trying to discourage anyone from building a wood pier, only providing my thoughts about why I used concrete.


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#8 Brent Campbell

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Posted 26 February 2021 - 11:21 PM

Several weeks without having to teeek polar alignment is still much better than the mount on a tripod.  Wood would also dampen vibrations.  I would have no issues with a wood pier.


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#9 ram812

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Posted 26 February 2021 - 11:35 PM

After looking of frost depth and other extremes I more than likely only have to go about 40" down. And with about 30" or so above ground I may give it a go. Sounds easy enough to me, and I hate kicking tripod legs anyway🤬.
CS, Ralph

#10 speedster

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Posted 27 February 2021 - 02:46 AM

It depends on what you are doing and what your expectations are.  A post in the ground beats a tripod for rigidity and set up time but a tripod is all it beats.  Good solution for something temporary and you might find it does everything you expect.  On the other hand, it takes little more effort or money to do something with less movement.  No one-size-fits-all. 



#11 michael8554

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Posted 27 February 2021 - 05:22 AM

According to the PHD2 developers, perfect PA is not necessary if you're guiding, 5arcmins or less is good enough.

 

All but the most expensive mounts will have Dec Backlash, so a small amount of Dec Drift due to PA error allows One-Direction Dec Guiding.

 

So I haven't worried that my wood pier PA may be varying, PHD2 seems to cope.



#12 alphatripleplus

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Posted 28 February 2021 - 09:17 AM

I've not tried one, but I think it is worth the experiment if you are curious about how well it would work.



#13 kathyastro

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Posted 28 February 2021 - 09:51 AM

I have used a plywood pier for several years, with good success.  It holds its alignment well, and damps out vibrations in ~1/4 sec.



#14 Berny

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Posted 28 February 2021 - 11:46 AM

When I posted this, I envisioned a pier that is constructed like a wine barrel with many individual staves, bolted to a concrete slab. I doubt that it would move significantly due to changing environmental conditions when used in an observatory. It could be a piece of art.  


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