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Frank's Observatory Pier Here is the progress on my observatory pier. For starters, I only have the pier at this point. I will hopefully be building a deck and windbreak walls in spring, then possibly a roll-top roof towards the summer or fall. I am quite proud of this pier, as I did all the work myself. I do need to give credit to the folks on the MAPUG (Meade Advanced Products User Group) mailing list who gave me a lot of sound advice on preparing for this project. Well, here are the details on how I did this, and I hope others can find this information useful. |
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First thing I needed to do was dig a hole. A BIG hole. Fortunately, my father has a backhoe, and was able to dig this hole for me. The hole you see in this picture is 5.5' deep, 8' wide by 4' wide. This was much too large and deep, so I had to fill quite a bit. I took some VERY strong chicken wire and made a ring 3' in diameter and about 2' tall. I took (2) 4' long 12"diameter sonotubes (one very slightly smaller than the other) and bolted them together with about a 6" overlap. Then I took an old steel tv antenna (the 3 1" tubes in a triangle type) and cut about 7' of it to use for reinforcement (not sure if this was the best move because the tubes, although steel, were hollow). --Note 2 years later- no apparent problems, pier is solid as a rock, however it's indoors now (see observatory)... I wired this pseudo-rebar into the center of the sonotubes, set this contraption into the hole so that 4.5' was below ground and 3' was above ground. I chose 3' because eventually I want to put a raised wooden floor around it. I set the 3' chicken wire ring around the sonotube, then filled in with ground around the wire circle to the top (about 2 feet) so there was a 2' deep 3' diameter hole around the sonotube. I then cut two semi-large round holes near the bottom of the sonotube so the concrete would flow between the inside and outside of the tube. At the top of the hole, I created a tic-tac-toe pattern with 2x4's to hold the sonotube in place while pouring.
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This part I did during the daytime while my wife was with the two kids (I
forgot to mention, we have 2 VERY young babies and they take almost all of
our time). The actual pouring of the concrete was done at night, believe it or not after the kids were asleep. I took 300' of garden hose, and 300' of electrical extension cord, and a 150watt spotlight (just the kind you need when observing deep space :-) ) and ran it to my observation site on the top of the hill, setup, and got ready. Once I was certain the tube was level and stable, I started mixing concrete. I took some rocks (limestone and riverbed rocks mostly) that I gathered from the field, washed them and randomly mixed them in with the concrete for strength and so I didn't need so much concrete. I first poured the base, then the tube. Every so often I checked the tube to make sure it was still level. While pouring the tube, I tamped the concrete down about every three shovels full to make sure there were no air bubbles. Once I got to ground level, I didn't use filler rocks anymore, just concrete for fear I may create an air pocket with a rock against the tube. |
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When I reached the top, I filled it a little more than even with the top of the tube, then set the bolt rig I created. Here's a description of this thing: I took a piece of 3/4" plywood about 14"x14", traced the sonotube onto it, found the center, drilled a 1/2" hole in the center, then placed my wedge onto the 1/2" bolt, set it so due-north points to one of the corners, and traced the wedge pattern. I then drilled 3 more holes (don't remember the size) to place the 3 wedge base bolts. Once the holes were drilled properly, I took a 1/2" j-bolt and used a nut and two washers underneath, and a washer and a nut on the top of the plywood. I took 3 12" all-thread bars, bent the bottoms into a J and bolted them onto the plywood in the same fashion. I left enough thread above the pier so I could put nuts and a leveling plate in if I wanted to but enough clearance so it won't interfere with the OTA. I took this bolt rig, set it into the concrete, and this was so cool- because it was dark, but the full moon was out, I turned the spotlight off, and I used not only a compass to point to due-north, but also Polaris! I finished the concrete phase at exactly midnight on a full-moon night. Is this an omen? Probably. The very next day it rained and rained and rained. Fortunately, I covered and wrapped the pier with a tarp in the morning. |
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The following weekend I took away the tic-tac-toe grid and filled the hole with ground. Notice- I did not fill the hole to ground level for two reasons: 1) I can't afford that much concrete and 2) I read too many vibration-related stories with concrete all the way up. After about a month, I'll pulled the cardboard tube off the pier and started using it. Believe me when I say it was WELL worth doing. I can't tell you how many times I have kicked the tripod leg and ruined a picture. It's also fantastic for quick setup- I do a polar alignment once every month or so. It really rarely needs even that. All I have to do now is carry the OTA and accessories up the hill, drop it onto the wedge (I bought a second wedge to keep permanently mounted on the pier) and go. Now my wait is the 20-30 minute cooldown for the OTA! I have plans to build a roll-off roof observatory around it maybe next year. This will cost a little more than I had planned for this year because I want to do this right with a wood floor, roll-off roof, electricity, etc. Oh yeah, one other thing I did- I stuck two all-thread bolts out the side of the sonotube about a foot-and-a-half from the top and about 6 inches apart. At this point I have nothing to attach to them, but I do plan to make a small shelf out of tin or aluminum for eyepieces, etc. down the road.
By the way, the total cost of the project:
I've added a link here for anyone who is interested in reading the MAPUG newsfeed thread that I collected with the credits to the various members who helped me. Again, I thank these people. Without their help, I'm certain I would have done quite a few things wrong. |
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