More concrete pier questions.....

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Hi all

Just in the process of planning a very simple concrete pier. I was thinking of basically bunging a single brake disc directly onto the top of a concrete tube (probably formed using some of that spiral air duct pipe) and connecting them with some thick threaded bars.

I’ve done a bit of research and have established that I need to use thick threads/bolts between the disk and top of the concrete tube to maintain stability, and also keep the gap as small as possible between the disc and the concrete for the same reason.

I will dig a reasonable base hole and re-enforce the concrete with rebar.

Now I’m not a great DIY guy so I have three (probably dumb) questions....

1 – I have read that the larger the diameter of the concrete pier the more stable it will be. I have a brake disk ready to use which is approximately 250mm diameter so was thinking of getting a 250mm diameter pipe to form the pier. However, I’ve noticed that a lot of people used thinner pipes than the pier tops/brake disks, is there a reason for this ? Might 250mm be too wide and risk collision between the telescope and pier ? I’m planning on using a skywatcher 200PDS on the pier to start with.

2 -  I have read a little bit about the ideal pier height but remain a little confused ! Lower is more stable, higher gives better visibility (really ?). I like the idea of lower is more stable (it might also help block a streetlight out for me) but does higher really give better views ?

I think I am settling for approximately 1m height. I intend to use this pier predominantly for imaging (currently with Newtonian reflectors) so would value any opinions on ideal height for this purpose.

2 – I’ve read that people recommend making a concrete pier in one pour but I am struggling to get my head around how you can pour concrete into a tube and not have it just run out of the bottom ?

I was thinking of making a frame for the hole, putting the rebar in place and then pouring the base first, then pouring the tube later on. However, everyone seems to recommend one pour so how is that done ? Do you do the base first and then pour the tube a little later but before the base has fully gone off ?

Thanks in advance for your advice.    

[Carbon Brush]

Hi. my two pennorth....

1/ Pier diameter. Put your scope on the mount you intend to use, on a tripod.
Tilt to the zenith and measure the distance from tripod centre to scope tube.
That will give you an idea of what restrictions a fat pier or big brake disc will give.

2/ Pier height. Is the pier outside? Will a shed follow?
The higher the pier, the nearer you can view to the horizon over nearby hedges, shrubs,etc. Assuming you are bothered about a low angle view.
But you are more exposed to wind, street lights, etc.
Taken to an extreme, you then need a step ladder to use the scope.
My pier is in a shed. Maximum pier height was dictated by the mount, topped by a level 10" newt OTA and roof still sliding.
That was the biggest (fattest) scope I could forsee getting.

3/ My pier was made in one pour. I got everything ready. The man with the cement mixer mixed and barrowed.
That left me free to check heights, levelling, etc.

Hope this helps, David.
 

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3 hours ago, Carbon Brush said:

Hi. my two pennorth....

1/ Pier diameter. Put your scope on the mount you intend to use, on a tripod.
Tilt to the zenith and measure the distance from tripod centre to scope tube.
That will give you an idea of what restrictions a fat pier or big brake disc will give.

2/ Pier height. Is the pier outside? Will a shed follow?
The higher the pier, the nearer you can view to the horizon over nearby hedges, shrubs,etc. Assuming you are bothered about a low angle view.
But you are more exposed to wind, street lights, etc.
Taken to an extreme, you then need a step ladder to use the scope.
My pier is in a shed. Maximum pier height was dictated by the mount, topped by a level 10" newt OTA and roof still sliding.
That was the biggest (fattest) scope I could forsee getting.

3/ My pier was made in one pour. I got everything ready. The man with the cement mixer mixed and barrowed.
That left me free to check heights, levelling, etc.

Hope this helps, David.
 

Thanks for your input David

1 - I've just done this, it measures 190mm from tripod centre to the tube so I am guessing this means a 250mm pier diameter will be OK then ?

2 - The pier will be outside, I have no room for an obs build around it unfortunately but will base myself in a nearby shed and run wires over to there. I’m lucky that I already have an excellent uninterrupted view to the horizon looking east (out to sea) but unfortunately the southern view has some nearby LED streetlights wrecking things and I was actually thinking of raising my garden fence by a few inches to shield the telescope from any stray light, so a low southern angle is a non starter 8(. I live on a bit of a hill and the garden gets quite windy but the pier location will be quite close to a fence and the house itself that should shield it from the prevailing westerly/north westerly winds.

3 – I’m still scratching my head a little with this, so when you fill the pipe how does the concrete not just push out of the bottom of the tube and spill out everywhere ? Or does that just not happen ? I thought doing it in 2 separate pours with the rebar in place to hold it together would be easier but that seems to go against general advice.  My mate has a cement mixer and will be helping me too so I hope it will all go smoothly !

 

 

[Cosmic Geoff]

Just an off-the cuff suggestion, but given that you are not proposing to build an observatory around it, would not a fixed tripod, or one of  these:

https://www.firstlightoptics.com/sky-watcher-mount-accessories/skywatcher-pillar-mount-support-for-heq5-eq6-series-mounts.html

or similar (these things are available in various heights) do the job just as well and be a lot less work?   And not be a problem if you move house?

I think those guys mean you cast the pier in one piece with the foundation, or how would you shift it?

I made a permanent wooden tripod to install in my garden and mount a lightweight telescope. It just sits on three wooden stakes.

[Carbon Brush]

If you are outside, and you do not anticipate exceeding EQ5/6 weight limits, then there is a good argument for putting the SW pillar on a concrete slab.

You can buy bigger/better steel pillars with larger price tags.

A 10" or thereabouts concrete pillar wil lnot ring like a steel pillar and if you get fed up of stargazing, you can put a car on it!

This comes back to foundation & pillar pouring.
In practice you getting a barrow full of concrete, then there is a pause while more is mixed.
From what I remember (about 11 years back) a combination the pauses in pour, and having decent ballast, meant that the pipe did not empty.
Concrete was tipped into the foundation and when we got to the top, I bedded the steel tube onto the wet concrete and arranged the 'keep vertical' bits of wood.
I don't remember any issues with the steel tube emptying.

Hope this helps, David.

 

 

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3 hours ago, Cosmic Geoff said:

Just an off-the cuff suggestion, but given that you are not proposing to build an observatory around it, would not a fixed tripod, or one of  these:

https://www.firstlightoptics.com/sky-watcher-mount-accessories/skywatcher-pillar-mount-support-for-heq5-eq6-series-mounts.html

or similar (these things are available in various heights) do the job just as well and be a lot less work?   And not be a problem if you move house?

I think those guys mean you cast the pier in one piece with the foundation, or how would you shift it?

I made a permanent wooden tripod to install in my garden and mount a lightweight telescope. It just sits on three wooden stakes.

Thanks that is interesting. I'm on a very tight budget so looking at the concrete pier as the cheapest (and perhaps sturdiest ?) option, also I hope to upgrade to an NEQ6 or similar at some point soonish and thought the brake disk option is a nice cheap way to accommodate that change.  

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2 hours ago, Carbon Brush said:

This comes back to foundation & pillar pouring.

In practice you getting a barrow full of concrete, then there is a pause while more is mixed.
From what I remember (about 11 years back) a combination the pauses in pour, and having decent ballast, meant that the pipe did not empty.
Concrete was tipped into the foundation and when we got to the top, I bedded the steel tube onto the wet concrete and arranged the 'keep vertical' bits of wood.
I don't remember any issues with the steel tube emptying.

Hope this helps, David.

 

 

That puts my mind at rest ! Thanks.?