Thanks all. You guys on CloudyNights are very helpful.
My only recommendation would be to not use those cheap washers and square nuts that come with the bolts. Get 1/2-13 stainless, which have much better threads and won't ever try to rust on. I'm sure you have already noticed that. I'd still stick a little grease or Vaseline in there, too. Re-bar in the concrete might also make sense.
That is the plan. I am getting 1/2" diameter 12" long SST L-bolts made at a price of CAD13.45 each (call it USD10) which seems a good price. And will use SST nuts. Good idea to put some thread lube in there.
Based upon personal experience may it is suggested that an 18" concrete pier is overkill for anything less than a 24" scope.
As to the bolts, even the lowest grade 1/2" bolts have a breaking strength of 10,000 pounds. Yes, as a professional engineer I assure you that they'll be adequate.
18" is pretty big. 0.96 tons. My buddy and I are building identical observatories, and he has an AP 1100GTO that will sit on a 10" pier. With a square base plate, his pier has holes on a 12" diameter. To get the bolts at least 2" from the edge of the concrete pier, that would be a 17" diameter. 18" is the next standard size up.
My pier for my Mach1GTO will be only 8". To keep things simple, both in-ground concrete piers will be the same, hence 18". Maybe I can get a bigger mount one day?!?!? My bolt pattern will support it.
10,000 pounds? So you are saying I should NOT put a 48" snipe on the end of my wrench to tighten the bolts?
Edited by t-ara-fan, 23 August 2019 - 12:38 PM.