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Metal or concrete ?


Teslar
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I think I'm settled on a metal pier but does anyone care to share their opinion of either metal or concrete with rebar for a pier.

Also any neat design or drawing of a metal pier would be handy as I may have access to off cuts and welding gear :)

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Well Tom I made myself a concrete pier which was encased buy a 8" brown water pipe, got the pipe from Noel but it doesn't cost much, 9 or 10 bags of ballast and a bag of cement, a half inch bolt concreted into the top then two 6mm steal plates seperated with 12 mm threaded bolts, then a bought altair Astro pier adapter fitted to the top plate, costs less than 130 pounds with the adapter which.cost 90 pounds,

It's at the height I want and is rock solid, a metal pier costs a lot more if bought from a shop.

If your interested you can see the build in robs obsy build, in the members equipment area or click on my Astro pages link in my signature.

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Before I built my pier, I read up about it on a lot of mainly American websites, MAPUG etc. Back then, about 13 years ago, the main consensus of opinion seemed to be to use a good strong steel pipe embedded in concrete and fill it with kiln dried sand and keep it dry and sealed in. The idea was that all structures vibrate, but the addition of the kiln dried sand on the inside of the pipe would dampen any vibrations very quickly. Apparently far quicker than they would dampen with a hollow pipe or solid concrete structure.


 


My pier was about 230mm in diameter with a 9mm thick wall, embedded in nearly a cubic metre of concrete and filled with kiln dried sand. I once got someone to give it a good wack with a hammer whilst I was looking through the eyepiece at about 300x and the image did vibrate very slightly but only for about half a second. So the above method worked well for me but there may be a new and different consensus of opinion on this subject now.


 


I know there are lots of good solid concrete piers around, but concrete can be a finicky material if not mixed perfectly to the right specification and could, in time, develop cracks and degrade in various ways.


 


You can see details of this here, though the site is now a bit dated...


http://homepage.ntlworld.com/peter.sullivan1

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I would say that concrete not mixed properly can degrade or flake, but mix it well with 9 parts ballast and 2 parts cement and a wet ish mix, tamp it down to remove air bubbles and it won't go anywhere, infact concrete gets stronger over time, modern concrete, cement mixes anyway.

It must last, the Romans were using it two thousand years ago on the builds and there still up.

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For me, I don't think I'd need a pier which was going to still be standing in 2000 years. If I ever did get one, I suspect it would be a steel one (made by Graham) which bolted down and could be removed. The extent of my imaging is just planetary and lunar and it doesn't matter if a passing truck caused any vibration (not that we have passing trucks). For me, the pier would simply allow a permanent set up inside an observatory, which is more important to me at present than an uber sturdy construction. If if the concrete in say Rob's pier rotted, it is all contained inside the plastic tubing, and has no where to go, so I don't think that will be a problem in Rob's lifetime.

 

I suspect it's all horses for courses.

 

JD
 

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For me, I don't think I'd need a pier which was going to still be standing in 2000 years.

 

JD

 

 

I broke out and disposed of the cubic metre of concrete and pier several years ago. It took some blood, sweat and tears and was the most back breaking work I've ever done! It took nearly two days and three successively bigger pneumatic road breakers to break up the concrete! It made the job harder since it was deep in a hole and the pier went most of the way down. Must have been a damn good 2000 year mix :D .

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Guest fondofchips

Steel pier as it is easier to change it if necessary, but all it needs is to be shorter with an adaptor that can be changed.


Which can be done with a concrete pier as well.


Have been thinking of using a hydraulic ram so raising & lowering doesn't involve spacers or adaptors, but then there is oil leaks & the inner ram can spin.


No one solution is perfect it seems.


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Guest fondofchips

I was thinking in terms of an old JCB hydraulic ram or similar & weld base & adaptor plates to it.


Just need to find the right length ram.


It does not have to be pretty, just functional.


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How about a Lorry air/manual bottle jack instead of the Ram.


 


Something like this


 


http://www.ebay.co.uk/itm/like/141127011670?hlpht=true&ops=true&viphx=1&lpid=95&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=95


 


Incorporating it and making sure there was little play might be a problem - just a thought !


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Guest fondofchips

I have a plan which involves 2 extensions to my pier as follows:-


4" & 8" high extensions which will connect to my EQ6 mount, then I can have 4", 8" & 12" raised height between them.


I'm trying to avoid the threaded bar method of adjusting the top plate.


Pier height has been my biggest problem, I am now waiting until the obsy is here before working out the pier height.


I cannot think of any other way to do it & I will have to cope with a reflector & a refractor so pier height has to be adjustable.


 


The hydraulic ram pier has one main problem that it would have tendency to twist in the opposite direction to the mounts movement, which might be a problem with AP.


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Is there any formula for working out the pier height or is it just what suits the scope and the user. I was thinking of having the center line of the scope aligned with the opening in the dome so that it has a clear view above the wall height if you get what I mean :)

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