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Concrete Pier Preparation and Construction

Gina

By Gina
in DIY Observatories

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Gina

Gina

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Been doing a "Fred Dibnah" - well it seems like it to me - heavy engineering! Been drilling and reaming the metalwork for my pier-head mount fitting. Mostly done except for the 4 holes in the bottom plate for the threaded rods that will be embedded in the concrete and the bolt for the azimuth polar alignment. I need to sort out the direction of north first - rather more accurately than my present guess.

Here are a couple of photos of current state-of-play :-

1) The two circular mild steel plates - 250mm diam x 10mm thick and the aluminium spacer plate the forms the pier adapter in conjunction with the 30mm hole in the top steel plate.

2) & 3) the top plates showing the shape to take the mount.

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Gina

Gina

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Thanks Malcolm and Michael :D All this seems to be such hard work - better be worth it ;) Pretty sure it will :o Much bigger stuff than I'm used to! Making up circuits and small scale mechanical stuff, writing software etc. is more my line. Plus dressmaking, knitting, cardcraft and suchlike.... Photography, water colour painting... ooh all sorts :o

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Digz

Digz

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Looks great! Nice work.

Remember to take into account magnetic deviation for your compass bearing.

It was 5 degrees west for me! Quite a bit when you think about it.

Keep up the good work!

Michael

That's a good point to remember, also mark north on your pier base without any of this metal hanging around otherwise you might get a false reading.

Btw looking good ;) I'm just in the process of designing my own pier and adapter it's great fun.

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Gina

Gina

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I already have a lot of iron in the pier and foundations as reinforcement and to attach the top fitting (threaded rods) so I'm proposing to take a piece of string from the pier towards the north then using compass, move until the pier is due south (allowing for the magnetic deviation). Then hammer a peg into the ground and tie the string to it. Finally, when I have the pier built I can take the string across the top and mark north on it.

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Gina

Gina

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Or use a Sun shadow at noon (well 1pm BST), potentially more accurate than using a compass, or use Polaris at night (not as easy!).
Good idea ;) More accurate and easier than a compass I think. I did think of using Polaris but thought that would be pretty difficult. I like the shadow at 1pm BST idea - thank you :o
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Digz

Digz

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Or use a Sun shadow at noon (well 1pm BST), potentially more accurate than using a compass, or use Polaris at night (not as easy!).

Now that could be a diamond idea, especially as you have threaded rods protruding out of the pier base?

I would suggest taking several 'readings' using one of your threaded rods to accurately find North.

Have a read of this:

How to Find True North Without a Compass - wikiHow

HTH

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Gina

Gina

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Thanks folks :o Guess what - following the suggestion of using the sun, it clouded over ;) Not to worry, hopefully we'll see the sun around lunchtime a few times before I want to put in the azimuth peg. No need until the pier's finished, although if I get the north fix I can finish the pier top fitting and paint it. A few days for the paint to harden before putting pressure on it would be a good idea.

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Gina

Gina

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There are web sites and/or posts showing how to calculate the size of iron pipes for piers but apparently nothing for concrete. Of course, I realise it would depend on the quality of the concrete. I'm just wondering if my concrete pier will be stiff enough. It's come out a bit taller than I first thought but I could raise the base and shorten the cylindrical top section. It's currently designed to be about 3-4 inches below grass level on average.

Here are the current designed dimensions (diagram not to scale) - anyone have any thoughts on this, please?

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Gina

Gina

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Been to Jewsons today and checked prices for a bulk bag of all-in-one ballast plus 7 bags of cement and they quoted £103 delivered. £41 ballast, just under £4 for cement and £10 delivery all ex VAT. That compares with the prices I found before of Wickes £92.52 and B&Q £73.90. Other firms I've checked are dearer. Now going back to B&Q website to check - best so far.

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Pug

Pug

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I don't know much about astronomy but I do know about concreting! 6 bags of cement to 1 ton (or approx 800kg) will give you the optimum mix of 5:1, if you mix it too strong there is a danger of it cracking.

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Gina

Gina

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Been back to B&Q website. I don't know how I found I could get 1 bulk ballast + 7 cement for £73 ish. Just tried and it looks like those items are not available to buy from the main B&Q site. When I go to their bulk deliveries site I can buy there (sort of) but minimum order is £100 and delivery is £20 up to £250. So even if the minimum order didn't apply, the delivery charge puts their price above Wickes. I guess when I checked B&Q prices before I didn't try to go all the way to the checkout page. So Wickes win ATM.

There are other things I shall want to complete my obsy, like conduit pipe to the house and materials for the roof and sides, so I think I'll sort those out before ordering and then they can all come in one delivery. I can't afford it this week anyway.

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Gina

Gina

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I don't know much about astronomy but I do know about concreting! 6 bags of cement to 1 ton (or approx 800kg) will give you the optimum mix of 5:1, if you mix it too strong there is a danger of it cracking.
Ah right, thank you :eek: I was going for 4:1 but I'll take your advice.
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malc-c

malc-c

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I don't know much about astronomy but I do know about concreting! 6 bags of cement to 1 ton (or approx 800kg) will give you the optimum mix of 5:1, if you mix it too strong there is a danger of it cracking.

Yup, 5:1 was the ratio I was using (still have 4 bags of cement left over for the next phase..) I found that 15 spade fulls of ballast and three of cement in the mixer just fitted into the B&Q barrow that I purchased Friday night :eek:

Seems OK so far

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Gina

Gina

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Got the bolts, nuts and washers for my pier top unit. Here's a photo of it assembled and mount attached. Still needs holes drilled for the pier rods and the plates painted.

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Gina

Gina

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That looks like it should be pretty stiff.
I think so.
I was just thinking how fast things have moved on from the first discussions on the Cumulus forum!
Yes, I think I've made some reasonable progress :eek:
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