Originally Posted by Bob_riggs  Hello Ken,
I install telescope piers for a living, and may be able to offer some insights. As you are in Florida, I'm guessing frost line is not a factor and 4' of buried depth is just fine, especially in sandy soil. I would suggest you consider using a 12" diameter pier foundation only up to 10" diameter fork mounted OTA's. You can downsize with GEM's due to the better balance. Bigger is truly better in this instance. An 18" Sonotube (or equivalent) costs roughly $8/9 per foot, uses little more concrete, but yields so much more stability.
The subject of steel reinforced concrete piers versus steel piers has pros and cons. Unquestionably, the concrete pier is subject to virtually zero vibration and flexture, and is much less expensive. On the other hand, if one is to move, that concrete hard to take with you, and it's nasty to remove. A steel pier is more portable in this sense, and gives somewhat greater ease of polar alignment.
If you chose to go with a concrete pier, you could bring your greater diameter up to grade/ground level, and pour a smaller diameter up to finished height.
There are good steel piers available for well under $1,000, and of course you can pay more for more features. If you'll PM me, I'll offer specifics. As to size, I mounted a 14" RCX400 on an 8" steel pier this last fall, supported on a 18" Sonotube column to floor height, under which was a 3 x 3 x 3 steel reinforced concrete block. It's "rock-solid".
I agree with your later post to install your pier(s) and build your obs around them, having determined the minimum working space needed. If your scopes are presently tripod mounted, you can arrange them in closest proximity to one another and see what's needed. Larger scopes require more clearance than smaller. Too much room is far better than too little. More concrete is better than not enough.
Hope this helps. Best wishes with your project.
Clear Dark Skies!
Bob |
02-20-2007, 04:53 AM
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