I wasn't sure how deep to dig the hole for the concrete pier footing. Conventional wisdom says to make sure it's below the frost line, but that's not an issue here in sunny California. One of my primary motivations for building the observatory was to eliminate the setup process, including the time-consuming polar alignment. My hope was that the pier would be stable enough to allow me to achieve a 'permanent' polar alignment, so I needed a stable footing. My plan when I started digging was to go 4' deep.
Post digger for the pier footing hole (click on image for larger version)
I soon discovered that digging a hole is hard! The soil in my backyard has a high clay content, and it's almost as hard as rock. Eventually I resorted to using water to soften it up. I'd pour some water in the hole, give it a few minutes to soak in, dig a few inches deeper, then repeat.
Using water to soften the hard soil (click on image for larger version)
By the time I got to three and a half feet deep, I was exhaused and decided to call it a day.
I ordered the steel pier from Dean Lewis at Midwest Optics. When I mentioned that I had gotten to 3.5 feet, he told me that was plenty deep, and I was eternally grateful! He did suggest that I widen it a bit to give the pier more stability.
I think that's deep enough... (click on image for larger version)
Added a couple of inches of gravel to help drainage (click on image for larger version)
Form to hold tube in place and make it easy to adjust (click on image for larger version)
Mixing concrete (click on image for larger version)
Footing with J-bolts in place and checked for level (click on image for larger version)