sonotube / Observatory pier design

Sounds good Al, two plates separated by leveling bolts seem to be the preferred option for alot of people but I've seen it mentioned recently that vibrations can resonate between the plates and into the scope. Not sure but maybe a slotted arrangement on the top plate that bolts tight to the pier when level may work. At the planning stage of a home for my setup at the moment myself so lots of ideas spinning around in the head. Hope the neighbours new addition won't be to intrusive.

Cheers
Reggy

Hi Albert,

I've been doing a lot of home work on pier design I recommend you have a look here first.

carlobeirnes wrote: Hi Albert,

I've been doing a lot of home work on pier design I recommend you have a look here first.

Thanks Carl,

I've read good things about the AE piers in the past. But I think that cost will dictate that I go with a concrete pier rather than a steel pier.

Mind you I wasn't planning on pouring a tonne of concrete into the hole! I'd thought that about half that, with wider base, about a meter down with rebar would suffice.

The videos also provide food for thought about connecting the pier to the wedge. I was going for the 'rats nest' approach to attach the wedge as it seems designed to be screwed from the bottom, though using more bolts and only leaving room for a very flat rat

I've been chatting to some people with a bit more experience in building and engineering than me and their suggestions pretty much match what people here have said in various threads.

For a concrete pier:
. Go down at least as far as the pier will be above ground.
. There should be a very solid base. The AE videos above mention a cubic meter, but by going down 4feet and using rebar not as much may be required.
. Wavin pipe (the water main kind) is expensive. Surplus lengths of 'storm drain' grade pipe would be good enough for this and is cheaper, and easier to find as off cuts.
. Ideally get roadstone to deliver the concrete. However since it is in a tube and a relatively small amount, an acceptable consistency could be achieved by mixing yourself. There are ongoing arguments about the optimal mix of sand, concrete and gravel

For a steel pier:
. similar guidelines for the base as mentioned above. Build the steel pier about 1m tall, then create the base to the correct height for the observatory.
. it will be more expensive (I'm sketching up something to get a quote on)
. about a 7inch diameter steel pipe will be needed. 10mm diameter. 18inch base plate.

For the connection to the scope:
. connect a 12inch square, 10mm thick steel plate to the top of the pier. Either welded to the steel one or with bolts sunk into the concrete one.
. connect an identical plate to the wedge bolted however the wedge needs to be bolted.
. bolt the two plates together using at least 4 1/2inch bolts. Keeping the plates as close together as possible.

I think the cost will end up being my main deciding factor so it will be interesting to see what sort of cost the steel pier would be.
Many of you have been through this process before, any other gems of advice or anything I'm thinking thats got glaring mistakes?

Thanks!
Al

Hi,

For the building foundations itself Wavin seems an expensive overkill. Sonotube is just cardboard that peels off when you are finished. Maybe there is a different name for it in Europe.

For the mount I used a concrete base. In February we bolted on a steel weld pipe to the base. I have been using it for the last few weeks and it appears very steady.

See: Variable Star Nights for images of the work (click under 'Building my Backyard Observatory').

John

Having built two observatories, these are my thoughts on piers etc

Forget about a concrete pier. Too may problems associated with them:
1. Ensuring adequate compaction during construction
2. Getting the height correct, especially in a rooll-off roof
3. How do you remove it afterwards if you have to?
It sounds simple and cheap, but it's not a good idea IMHO.

I recommend a steel pier, but forget about those you see advertised on astro shops - waaaaaaaaayyy overpriced.
A local fabrication shop can make a better one for a lot less.

My steel pier is: 200mm x 200mm box section x 12mm thick.
The flat plates on top and bottom are 350mm x 350mm x 12mm thick and are welded to the box section.
Box section are cheaper than circular.

My foundation is 600mm x 600mm square x 600mm deep concrete.
Make sure you dig down to solid ground and surround the excavation with damp proof membrane (DPM) before pouring the concrete.
Remember, you don't need a scud missile launch platform...just a foundation.
This takes my Paramount ME, 16" SCT and TEC140, with no problems.

To put the foundation dimnensions into perspective, the standard house foundation is 900mm wide x 300mm deep.
The load of a telescope, mount and pier is absolute peanuts in comparison.

If you are pouring a concrete slab all around it, make sure you leave a gap of few inches between the floor and the foundation.
This will help to reduce vibrations from travelling into the pier.
If you wish to avoid the use of reinforcement in the slab, you can get fibre-reinforced concrete delivered.
This will cost an extra approx. 30-40euro (depending on quantity of concrete) for the addition of the fibres but is much easier to lay than having to fix steel.

In terms of piers, I suggest the use of a double-pier system for a roll-=off-roof observatory:
1 short pier bolted on top of a much higher pier.
Why?
At this stage you have X size telescope.
However, in the future, you may want to upgrade.
If you have a roll-off-roof, how do you fit the bigger scope/mount if the pier is too high?
This is particularly a problem with concrete piers where cutting a piece off a concrete pier if very difficult.
By having a double-pier system, you can always remove off the stubby little pier to allow for the upgrading to a bigger scope/mount in the future.

You are more than welcome to pop down here and take a few photos if you wish.