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Concrete Pier Preparation and Construction


Gina
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You could always contact your council and tell them you need one of their composters, think ours cost about 15 quid.....you won't have any size issues with that :)

Have fun playing with the EQ6, it's beautifully clear here, so i'm off to set up....hope it holds clear for you to play....

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Have you looked at aircon ducting at all? That appears to come in a range of diameters from 100mm to 300mm. Filled with concrete it could probably be left in situ. A builders merchant might be able to get a single length at a reasonable price.

I found today that the electricity pylon at the end of our drive is going to be replaced in a couple of weeks because Western Power have decided it's "damaged". I'm half-tempted to get them to leave the old one behind as a potential pier. It has a stonking great 11kV 3-phase transformer on the top, so it must be fairly robust.

James

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I have looked at air ducting but only found 125mm so far. I'll do a Google search. Good thinking. :)

Is it a wooden pole? Plenty strong enough but would it be free from movement, I wonder.

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I have looked at air ducting but only found 125mm so far. I'll do a Google search. Good thinking. :)

Hiya...I went for the air-duct option with "re-bar" concrete reinforcement in the centre...

Some pictures here showing how it all worked out...

Cheers

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I will probably be using something like this and fill with concrete:

http://cgi.ebay.co.uk/110mm-x-3mtr-Underground-Plastic-Drainage-Pipe-/300488863432?pt=UK_DIY_Materials_Plumbing_MJ&hash=item45f6882ec8

The pier shouldn't be too wide in diameter, especially with Newtonian telescopes, otherwise the mirror end of the scope might touch the pier when viewing objects straight up.

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I didn't think 4" or even 6 or 7 would be strong enough. But OTOH, 4" square concrete fence posts are pretty strong and rigid if concreted in. I agree that the pier doesn't want to be too wide. How wide is yours, Chris? Your setup looks great :)

Incidentally, Chris, I see you're only a few miles from me - I live near Upottery.

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I agree that the pier doesn't want to be too wide. How wide is yours, Chris? Your setup looks great :)

Incidentally, Chris, I see you're only a few miles from me - I live near Upottery.

Thanks :eek:

I posted the pier dimensions, parts and costs in this SGL post.

If you wanted to take a look at my completed pier before you commit your time, efforts and money, I'd happily welcome visitors...just send me a PM.

Good luck!

Cheers.

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I didn't think 4" or even 6 or 7 would be strong enough. But OTOH, 4" square concrete fence posts are pretty strong and rigid if concreted in..........

Here is an obsy build that uses this kind of pier:

http://stargazerslounge.com/diy-observatories/103639-wetherview-diy-obsy-build-begins.html

Might be worth asking Wayne how stable / rigid that pier is....

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Thanks for all your replies :) Good food for thought. I was thinking in terms of around 12" diameter but now downsized my ideas to something like 5-6". I'm currently setting up my 130mm Newt on the EQ6 mount on tripod near the obs site. Looks like clear skies tonight so getting quite excited :D

Thank you for your offer Chris - I'll bear it in mind :D

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Setting up the mount is taking a bit longer than anticipated but I am learning things and finalising plans for the pier etc.

Two circular 250mm diameter by 10mm thick steel plates are on order.

4 M14 x 1m galvanised threaded rod

M14 nuts and washers

1 bag cement + 4 bags ballast - chap at Jewsons thought this would do me.

3m of rebar plus assorted scrap iron

Misc lumps of concrete block and stone

Hole now 36" x 30" x 30" deep which I think will do :D

Tripod height is 29" ATM and plenty high enough - critical part is getting at EP of polarscope. Probably 2ft would suffice for height of bottom of mount - I can lie or sit on the ground to polar align since it should only need doing once. I should not need to get to the bottom of the scope when looking vertically up once it's all set up on the mount as the latter will position the scope roughly (if not exactly). The steel plates will want to be something like 8" apart I guess (must measure the length of the mount fixing bolt). So the pier need only be 14" or so above floor level, making it something like 20" above the top of the block.

I'm thinking of making the pier around 6-8" diameter. Now I have a cardboard mailing tube 7" ID and about 7.5" OD and 3m long that plumbing pipes were delivered in, and I'm thinking of cutting off a section of that to mould the pier. A 7" diameter concrete pier with 4 M14 threaded rods as rebar and to take the bottom plate, I think would be fine. Then I think some lengths of M12 threaded rod near the edge of the 10" plates to connect them together.

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Hang on!! What the Jewson's man gave you was the RATIO of cement to ballast ie about 1:4 or 1:5 will be OK.

Use this: On-Site concrete calculator.

to calculate what you need - I've appended a rough calculation which is probably a little "over". You need to ADD the sharp sand and aggregate figures if you are using bagged ballast. Plus you can deduct some for the stone you will be using as "filler".

post-17157-133877597467_thumb.jpg

Edited by Bizibilder
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Well, I thought it didn't seem enough but I told him the size of the hole I was filling and that I was building a pier on top. Anyway, I'll start filling the hole and see how it goes, I can go and get more if needed. I shall be using plenty of rubble and lumps of stone and concrete in the hole and some smaller stuff in the pier. Or maybe I should use just ballast and cement for the pier. I'm not a builder.

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When you do the pier itself (as opposed to the block), make sure you have enough concrete left to do it in one go, otherwise you will get a weakness across the pier where the join is. The block isnt so important as most of its job is just to add weight and stability. Again, I would only put the rubble in the block as you could get a weakness in the pier...

Cheers

Edited by citaylor
typo
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I should have said - when you come to do this, unless you have several strong men (and women!!) around to do the job it is well worth hiring a concrete mixer. Concrete is HEAVY and you would soon tire of mixing it. It really should be mixed and poured in one go and it does not "bond" very well if you make lots of small amounts.

If you are in any way "not quite as fit as you should be!" then a mixer is almost essential - a damaged back is not much fun - so I've been told.

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It's alright - we have one :D Yes, that sure would be a lot to mix by hand!!

Thank you for confirming that I shouldn't use rubble in the pier, Chris :) And, yes, I realised the top part of the block and the pier wants pouring in one go. I'll do the bottom half or so of the block and see how much it uses. Then make sure I have more than enough to finish the job.

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The mix he used was a bit dry by the looks of it. One thing I don't get is everyone bangs on about having 1cu mtr foundations, then solid piers but then support the weight of the mount and scope on three relatively thin bolts !

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Its all to do with "amplification" - the tiniest movement or vibration at the pier base will be much bigger at the telescope. It also has a damping effect - large masses are better damped than small ones - so any vibration dissipates much more rapidly. The bolts people use - usually 12-16mm are at the "light" end of the system - I would be much more concerned by the relativly flimsy attachment of dovetails to mounts and the thin walls of most scope tubes.

Edited by Bizibilder
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I think I might widen out the pier at the bottom to reduce the stress where it's greatest. I have yet to work out how I shall support things while the concrete sets but we have plenty of bits of wood so shouldn't be a problem. I don't like having a sharp change of angle just where the stress is greatest. A conic section pier, smaller at the top and bigger at the bottom with a curved transition to horizontal would be my thoughts of an ideal structure. Or even a wider angle conic section going out to the edge of the block.

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Been hammering iron pipes and things into the bottom and sides of the hole. Two one inch galvanised water pipes and two pieces of rebar hammered into the bottom and extending most of the way up the pier. The four M14 threaded rods will overlap these and continue the reinforcement up the pier. I've bent the bottom end of the threaded rods to prevent them possibly pulling out

Edited by Gina
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