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Astrodude (sorry - I don't know your real name), Regarding choice of 457 mm dia former, there wasn't a lot of science; it was a gut feel thing, but I did know that I wanted to allow for a decent size scope in the future, and also that the stiffness of steel pipe varies as the fourth power of diameter. I figured that I might end up using some pipe maybe 10 inches or so in diameter. In fact the scrap that I got was 11" pipe (1/4" wall thickness) and the final result is very good in terms of stiffness. If I kick the pier, the high frequency vibration settles down in under 1 second, and I can't detect any low frequency vibration.
The other consideration with concrete pier diameter is that you don't want the bolts too close to the edge. Let me know if you'd like any other details of the cage or pier.
Cheers,
Chris
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