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Gina

Concrete Pier Preparation and Construction

159 posts in this topic

Got a couple of large plastic plant pots which I've cut the bottoms out of. These will fit below my 7" ID cardboard tube to widen the pier base out to about a foot diameter. That should increase the strength at the point of greatest leverage.

Hoping to start pouring concrete tomorrow. Bought some more ingredients today - realised (was told) I didn't have enough.

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The steel plates for the mount have arrived so one step nearer :) OTOH the very chilly easterly wind has got up more and black clouds are gathering with spits of rain in the air so concreting is postponed for now.

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Having measured up my mount I have come up with a simplified design for the pier adapter.

Apart from the top steel plate (250mm diam x 10mm thick), I plan to use a 5mm aluminium plate with a 65mm diameter hole as shown in the diagram attached. The steel plate will have a hole cut to take the boss of the mount. Then the mount can be attached with a 12mm bolt, washer and spacer. The top steel plate I propose to connect to the bottom steel plate with 4 12mm bolts (or threaded rod) around the edge to allow space to get to the mount attachment bolt. The lower steel plate attaches to 4 14mm threaded rods embedded in the concrete pier.

post-25795-133877599448_thumb.png

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Here's the design of the whole pier top section. M14 threaded rod in the concrete attached to steel plate. M12 bolts or threaded rod to the top steel plate then aluminium plate to provide base for mount as described above.

Anyone see anything wrong with this design? Or any suggestions for changes? Saves a lot of money on a manufactured pier adapter.

post-25795-133877599558_thumb.png

Edited by Gina

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Looks good to me... I'll be using your design when it comes to doing mine... as you say, cheaper than having a custom one made up out of steel etc.

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Thanks Malcolm :) Got the steel plates and now have the aluminium plate on order. It's 200mm square by 5mm thick. I'll have to trim off the corners to stay within the 250mm diameter of the steel plate but that shouldn't present any problem.

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Not quite sure why you have put the Ali plate in? (Maybe I'm missing something!). Otherwise it seems a good design.

Edited by Bizibilder

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This was my effort. Made from mild steel I had lying around.

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This was my effort. Made from mild steel I had lying around.

Is that the one in your obsy?

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No, this is one I knocked up for my refractor. I mounted the EQ & tripod dock directly to the concrete pillar in my obsy. Adapters are OK if you want to remove the mount regularly but what you have to think if your pouring 1/2 a ton of concrete in to the ground and pier you don't really want to end up relying on only 3-4 M12 studs holding your mount and scope. Just doesn't seem worth all the effort put in to creating a stable pier if your going to introduce a weak link.

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A fine looking scope if ever I saw one :)

Didn't think the pier looked the same....

Edited by rawhead

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No, this is one I knocked up for my refractor. I mounted the EQ & tripod dock directly to the concrete pillar in my obsy. Adapters are OK if you want to remove the mount regularly but what you have to think if your pouring 1/2 a ton of concrete in to the ground and pier you don't really want to end up relying on only 3-4 M12 studs holding your mount and scope. Just doesn't seem worth all the effort put in to creating a stable pier if your going to introduce a weak link.

I think the relatively thin bolts / threaded rods do actually take away a bit of vibration. It's a bit like putting speakers and turntables on spikes.

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I could replace the M12 supports with M14 if I found any problem.

Not quite sure why you have put the Ali plate in? (Maybe I'm missing something!). Otherwise it seems a good design.
The ali plate is instead of making a 65mm diameter x 5mm hollow in the steel plate to accommodate that shaped "sticky-out" bit on the bottom of the mount. I haven't got a router, just a bench drill with various bits and a jig-saw. The mount sits on the outer part of the tripod top and the central spigot (30mm diameter and 15mm deep) stops horizontal movement. It would be less stable if it sat on the 65mm diameter piece rather than the 130mm diameter.

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Ok, I see now. (I have to admit to having a metal workshop and I forget how tricky a simple "hole making" exercise can be!).

May I make a suggestion - that you paint the Ali and steel all over to prevent any "different" metal to metal contact. If you don't corrosion will be a real problem especially in wet or damp conditions.

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Yes, I expect to do that - the steel plates are ordinary mild steel and want painting anyway. I don't like bare metal unless it's stainless steel or anodised ali (but you can't really call that bare). I'll probably use Hammerite.

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I could replace the M12 supports with M14 if I found any problem.

.

Don't get me wrong Gina you may never have a problem. If it is necessary to remove the mount after use then there is no real alternative. The point I was making is that in a permanent set up it's a weak link that can be avoided. I have seen some piers constructed on the internet with huge holes filled with truck loads of concrete, rebar etc and then they mount their 10" OTA EQ5 combo raised up on 3x 6" M12's :)

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The point I was making is that in a permanent set up it's a weak link that can be avoided. I have seen some piers constructed on the internet with huge holes filled with truck loads of concrete, rebar etc and then they mount their 10" OTA EQ5 combo raised up on 3x 6" M12's :)

The format of using threaded bar / bolts to support a plate / mount head seems to be the normal practice, irrespective of the pier being a metal tube with a base plate or concrete pipe buried in the ground. I can see your point, but what's the alternative ?

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I've sorted out what I'm using to support the concrete in the pier. Two plastic plant pots of different sizes so that the bottom of the smaller on fits the top of the larger one and the bottom of the small one just fits inside the 7" ID cardboard tube. Needless to say, I've cut the bottoms off the plant pots. This gives a base of a foot diameter where pier meets the block.

I haven't started pouring concrete but today I have been collecting all the bits at the work site. Cement mixer, dustbin full of water, cement and all-in-ballast, large stones and broken concrete to eek out the concrete in the bottom of the hole, some more reinforcement bits and wood for supports.

Note - Although the diagram shows a join at the pier base, there will not be one - I shall pour the top of the block and pier all in one go (the colour/pattern fill produced that line).

post-25795-133877599684_thumb.png

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Here's a bit clearer diagram of how the plant pots and cardboard tube fit together.

post-25795-133877599767_thumb.png

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The format of using threaded bar / bolts to support a plate / mount head seems to be the normal practice, irrespective of the pier being a metal tube with a base plate or concrete pipe buried in the ground. I can see your point, but what's the alternative ?

If you have no alternative but to remove your mount Astro Engineering AC389 The "Owl's Nest" Altazimuth Mounting Barrel for all Piers or a similar construction.

If you have a permanent set up you set the threads in to the concrete pier as you would anyway then drill a shallow hole in the center large enough to accept a 17mm bolt head. Get a steel plate (thickness depending on needs) drilled the center and 3 or 4 holes for the fixing studs. Fit the plate establish north and drill and tap a hole. Screw 3 nuts up a M6 bolt and the tighten in to the north hole in the plate for polar alignment. Remove the legs from your tripod and then tighten the mount/tripod to the plate using a regular M10 bolt with spring washer and fit flush to the pier. Any leveling needed can be done by sliding washers under the plate and once done tighten down solid. Doing it this way can mean a bit of fiddling to get PA and leveling correct but once done it shouldn't have to be done again.

I hope people get where I'm coming from as why make so such a great job of a pier only to end up relying on 3 or 4 12-14mm studs to do all the work :)

Edited by spaceboy

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I've seen that design incorporated into some DIY piers. I think the main reason people use the rod/concrete/bolts and top plate construction is costs and convenience. Most of us own a drill and can acquire the bolts etc from B&Q, but access to and experience of using welding equipment is another thing. One other factor is trying to find a small company willing to make the pier for a reasonable price, or here in the south just finding a small local engineering company is a challenge !

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You have probably though of it already ...

But watch the "joint" in your flower pot shuttering doesnt come apart when you pouring your concrete... you also want to avoid excessive loss of the "liquid" part of the mix through the joints.. duct tape may be your friend...

Peter...

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I had plans for fixing the joints together for stability but didn't think of liquid loss. Tape is a good idea - thanks for the tip :)

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