Telescope Pier

[Ian]

I'm thinking about putting a pier in my garden, has anyone got any experience of building one?

[Rocket Pooch]

No, but I tell you what I do have, a 1" round 3" high carboard tube.  I was thinking of filling this up with cement and making a piller.  All we would then have todo is bolt a plate on top for the mount.  I'll help, esspecially if its in your garden because it will be a safe prototype for me

[Rick]

Hmmm... This stands a chance of becoming technical...

Didn't Greg have something to say (on the Magical London Astro Tour last summer) about the lump of concrete in the back garden of Steavenson's old house? Something about it going down fifteen feet?

I'm fairly sure, if you want the pier to be (a) stable, and (b) fairly isolated from vibration caused by people walking around, then you do need it to have fairly deep foundations, and you need a floor around it that's not well coupled to those foundations.

Try searching the ATM mailing list archives.

[Ian]

Actually I should hope that it does get technical, should've posted in the right forum. Must learn about these newfangled things one day

My trouble is that I can find very little science in peoples approaches to piers. If the pier is to support a large SCT or RC scope, fair enough, but the engineer in my head is telling me that building a pier set in more that 1 cubic metre of concrete is probably overengineered. Particularly as I found a site last night describing a pier made out of a 100mm square wooden fence post. Since I am not prepared to bury a metre of concrete in my back garden, I think I go as minimal as I think I can get away with and see how it goes. The problem that I now face is, how minimal can I get away with?

[Rick]

I have a pier mount for my Newtonian, and it sits on specially levelled paving slabs in my back garden. Or rather, it used to. The general unsteadiness of the soil round Orpington means that I should really lift and re-level the slabs....

What's the rule-of-thumb on foundations? Something like they should go down one third the height of the structure they're supporting? One quarter?

[Rick]

As an aside: The pillars that form the Otford Solar System model are set in a lump of concrete 600x600mm square, and 400mm deep. Each pillar is 1.3m high and 450mm in diameter. The 600x600mm base is a standard square paving slab.

[Ian]

well the foundations for my conservatory are 0.5 metre deep. But it is difficult to apply these sorts of rules of thumb since the requirements on a pier are rather different to a building.

How heavy is that solar system model?

[Rick]

Take a look:





[ This Message was edited by: Rick on 2004-02-05 15:25 ]

[Whitters]

The thing about a conservatory is that it may be only .5m down, but it has a large wide footprint.  Therefore local variations in the soil are unlikely to be noticed, the conservatory is also tied into the building in some way and therefore has further stability.
With a pier you will be walking round it to observing and such, compacting the ground. Also if your garden is anything like mine, on London clay, the ground gets saturated in the winter and dries and cracks in the summer. Small items like a fence post require a foundation deep and wide enough to prevent them from being moved arround by the small scale movements of the ground.
Finaly the advantage of a pier is that you can perfect your polar allignment, the last thing you want is insufficient foundations for your pier being moved by local ground movements and throwing out your allignment.


[ This Message was edited by: Whitters on 2004-02-05 19:25 ]

[Whitters]

Maurice Gavin's observatory
http://home.freeuk.com/m.gavin/mydome.htm

Quite a technical discussio on the subject of home observatories.
http://www.homedome.com/athome.pdf

[Rick]

Those links look good. I've only skimmed the second one though. It's quite long...

The Otford Solar System pillars weigh in at about a quarter of a ton each.

[Ian]

now that PDF makes interesting reading.

I think I'll probably go with my current idea of using five lengths of 90mm fence bolted together and probably bury it about a metre underground. My telescope is not the heaviest, wood provides a high level of damping to vibration. I'm not expecting it to last decades, but a few years would be nice.

[Whitters]

sounds like a sensible option

[Rick]

The spec for the Otford Solar System model said  it should stand a chance of lasting a thousand years....