Request advice re positioning pier onto base

[peter brown]

I have decided tonight, to purchase a Sirius 3.5m observatory for all the obvious reasons. Iam planning dig a great hole in our orchard after chopping down a cherry tree. At the top of this pier foundation it will narrow to a vertical cylinder to the proposed height of the observatory deck. I plan to make a dummy pier base plate , attach my anchor bolts to it, then push it into the wet concrete. After the concrete sets, I will unbolt the dummy and remove it, leaving the protruding threaded ends ready to accept the pier after all the rest of the beautiful thing is constructed.
I will be mounting an meade ultra wedge onto the pier.
Question: Do I have to orient the pier in relation to the true poles of the earth or can I manage to get polar alignment by manipulating the wedge. Once the bolts are set in concrete I had better have got it right!
I have ordered the observatory, arranged with a buider to construct the deck but need some advice about constructing the foundations and orientation of the pier to hold up meade ultra wedge and lx200gps 10" scope.

Would welcome advice

Peter B:help::help::help:

[JimmyH155]

One piece of advice regarding the concrete. When you calculate how much to put into the base plate, use the same amount as us Engineers do to secure pumps onto base plates. Use a minimum of 5 times as much concrete as the whole scope weighs (ie if it weighs say 50 kg, then use concrete 5 x 50 = 250 kg of concrete, or roughly 0.25 cubic metres (thats a cube of 630mm x630mm x 630mm. If the pier is quite high, though, I would add more, because overturning moment would increase the higher the centre of gravity is. You dont want it wobbling just as you are taking that winning photo:D

[BOBBY]

I am in the process of doing the same thing. I have the dome and have just completed the decking. For the foundation I dug a hole about 650mm sqaure and about 750mm deep. I used a old Oxy/Acet bottle that I gas axed the top off and welded to the top, a mounting plate about 400mm diameter. This is concreted in the ground and rises about 500mm above ground level with the plate being flush with the top of the deck. I am using a Bintel pier thats already machined to suit the LX200 wedge its also marked with the position its to be orinintated (South) I lined it up using a compass and bolted it to the mounting plate (18mm shoulder bolts).Any discrepencies in the level, direction etc can be made on the super wedge (I hope) Anyway this weekend I am erecting the dome, wedge and scope so I will let you know how I get on

[JimmyH155]

You didn't really gas axe the top off an oxy bottle:scared: did you??? Many people have done similar things and are no longer here to tell the tale:eyepop:

[leon]

Bobby you are kidding, surly

leon

[Ian Robinson]

would want to have been very well purged with compressed air and vented to ambient pressure....

A thick walled steel tube of the right height , and maybe 200mm OD , would be my choice.

[Lee]

The density of concrete is around 2.3g/cc, so 250kg of concrete takes up much less volume than 0.25 cubic metres - more like 0.1 cubic metres.....

[JimmyH155]

OK Lee, yes, I know. I've never been known to skimp on stuff like that. The more mass the better, so pretend its SG is 1:D

[bluescope]

I've seen guys use plumb lines at local noon to get true polar alignment when setting up piers. Here's a link ...... hope it helps !

http://www.shelterinstitute.com/tips/truesouth.htm

Summary:

1) Calculate Solar Noon - NOAA has a nifty web site that calculates this for you:
http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html

2) Hang a plumb bob in the sun (a little before the time of solar noon).
3) Precisely at solar noon, trace the shadow the plumb bob string casts on a horizontal surface - this is the line of true north/south!

:thumbsup:

p.s. Just found a solar noon calculator that gives you a calendar for the whole year ..... handy to print out !

http://www.spot-on-sundials.co.uk/calculator.html

[JimmyH155]

So instead of needing an accurate compass, you need an accurate watch:D;)

[bluescope]

Well you should only need to do it once !

:thumbsup:

[rally]

You don't say how high the dome and deck is to be from the ground.
How high ?
The higher it is the larger and deeper your foundation should be.

I recall reading about people who are subject to freezing earth (which you may be ?) and the effect that this has on moving the entire structures.
The solution is to ensure that the foundation is below the ground level that can get frozen.
Of course the type of ground you are digging into is relevant here also, eg soft water laden earth Vs rock etc etc makes a difference.

At the end of the day your pier is only as good as the weakest link - that also depends on the diameter and wall thickness of your pier (and material !).
Since you are going to lots of trouble to create a good imaging platform, dont skimp on the last $100 on the pier material - it is what makes all the difference.
What diameter and wall thickness did you have in mind ?

Cheers

Rally

[BOBBY]

Hi Peter
Got the dome errected at the weekend, apart from a couple of cock ups (not reading the instructions) it was a doddle. The scope is installed just require a good night to get everything sorted. I would mention that I have the home model thats only 2.3mts and with the 12" there is stacks of room, you mention the 3.5mts unless you plan to put somthing bigger than a 10" it will be an overkill, spend your money on a decent CCD .
In regards to the pier you could swing a Mack Truck of it, I think some guys go a little OTT in regards to concrete densitys, ree bar diameter etc
Anyway have fun a will attempt to post some pictures later on.

[peter brown]

I am glad that your observatory has gone up so well.
Did you use a pier from meade. I bought one, it is 1 m. high and has a small arrow on it. I am now waiting for my ultrawedge that I am getting via a devious route from the US as the agents in Aus have orders waiting from before Christmas. I did order the 3.5m obs. on my wifes advice as she wants me to be set up properly for my retirement and not wish I had got a bigger setup.
Does the little arrow have to face polar south?
How much lateral movement does the wedge have, to allow for less than acurate polar alignment of the pier.
My wife has also brought in a professional builder to erect the platform and pier on concrete poles and takeover installation of the observatory when it finally arrives....
I am only a lowly GP in the bush...gotta step back and let the others have some fun with my toys as well:whistle:

Did you have to move the pier forward so that the declination axis of the scope on its arms would be in the middle of the observatory?
I have lots to think about but would value any tips from your recent experience

cheers peter b

[Hagar]

Hi Peter. Take a look at the drawing on the attached page it shows a telescope similar to your LX200 mounted in a dome and would indicate you need to mount the scope pivots in the center of the observatory. This actually makes sense as you need to be able to follow the opening in the roof.

You could give Peter Ward at www.atscope.com.au (http://www.atscope.com.au) a call he sells them and would know of the mounting reqiuirements. You could also Personal Message him on this forum.

Observatory layout.... http://www.atscope.com.au/sirius.html

Good luck with it and if you need a hand just call.

[JohnG]

Hi Peter

Here is a link to the complete construction of a 2.3m Sirius Obsersvatory, from 1st sod to completion.

Doug (Hagar) has seen it and can comment on it to you in person.

http://www.pbase.com/takman2/new_observatory

Cheers

JohnG

[Hagar]

G'Day again Peter, Just having a poke around on the net. It appears you may well not need to mount the pier off center as the way the scope and the wedge are configured the center of pivot may well be around the center of the pier. Check out the following link.

http://www.richobservatory.com/Site/Equipment.html

It may pay to wait until you have the wedge and set it up on the tripod and make some measurements.

[astro_nutt]

Hi Peter
Congrats to you on building the Observatory...
I read somewhere of using 3/8th" bolts with the threads covered in gladwrap and the shafts welded to a steel framework before attaching this to a wooden baseplate and setting in wet concrete..worked like a charm..
Cheers!