Building an observatory pier

I'm also planning an observatory here in rural Raheny!

I'm actually thinking of something like this

My problem ir that I plan to mount my 12.5inch newtoinian on an equatorial mount and I'm gonna need a lot of space so it can swing 360 degrees. One of my long term objectives is to make this fully automated and internet accessible. Thats a few years down the road and I may well relocate it to a less light polluted area.

I'll post info as it progresses.

Clear skies,

Dave.[/url]

To Dave L, Thanks for that info. I'm thinking something similar might be appropiate for me and I don't have to go to a metalworks to get it done since I'll do it myself and lower the costs.

To Dave G, Will U be at the meeting on Tuesday evening? If so we'll have a chat.

Spaceboy

Spaceboy,
Nice one if you can do the metal work yourself, i just wouldn't do the welding myself, since I need it to be good. :lol:

Heres a pic of the mount i use, I put the ETX70 on it for scale.

www.irishastronomy.org/user_resources/fi...254-Pillar+ETX70.jpg

I left the protruding bars underneath and will cut them off when I have the dome built.
Some of the bolts are slightly rusted, these I'll change over the next few months.

When it comes to filling the pier with something, sand is a reasonably good material. However, if dampness gets into it (which it could very well do) then the effective of the sand decreases alot. Basically, sand consists of alot of small round particles. The fact that they are round means that they don't compact too well. However, if you wet the sand, the viscosity of the water tends to fill up the void spaces between the grains and stick the grains together. Wet sand in a pier is not desirable as it will resonate vibration much easier bacause the vibration travels across from one grain to another through the water. You end up with a semi-sold internal portion to your pier.
If you are concerned about dampness hitting the sand, you might decide to select a material with larger particles, all of similar size. Therefore, coarse dry sand or small single-sized stone might make a better choice.
When selecting a small-sized stone to use make sure it is of roughly all the same size aggregate. Beach or river gravel would be much better than normal crushed stone as it is rounded due to the action of the water. Rounded particles don't compact too well (think of marbels) which is why river or beach gravel is never used (or at least SHOULD never be used) for constructing something on. The fact that they can't compact means that they have room to move around a bit. This is what you want in a pier as the movement of the particles actually disapates the energy thus reducing vibration.
A point will come of course when too large an aggregate size will mean that vibration will go up due to insufficient material in the pier to take vibration. However, my gut instinct tells me that this wouldn't happen until you were using something very large stone. Therefore, when selecting a material to fill the pier, I don't think people need to restrict themselves to only sand.
(end of geology lecture! )
Clear skies,

Nice mount for the ETX Dave!

Michael,
Going on what you say above, maybe something like sharp sand (for patios) would be a good choice as it compacts well.
By adding this sand or any material, you're reducing the resonant frequency of the pillar, which can be but isn' t always the best thing to do, so I've heard ?!?