Construction work on the observatory started in January of 2013. We had a local contractor, Chatters Construction, do the work for us. They built our home, garage and studio that is located on the same property. We picked a location close enough to our main residence such that running electrical and internet connections was not prohibitive, but far enough away to keep stray light from the residence down to a minimum. Overall size of the building is 10’6″ x 13’6″. The pier is offset to allow room for a small desk on the north side. The dome is actually square on it’s bottom flange and the building was built to accommodate.
You can just make out our residence in the upper right corner. After marking comes digging!
Note the hole in the ground for the pier foundation. At the time this was a 3’x3’x3′ hole.
The walls are going up.The ground was mostly level. There is a slight downgrade from the back of the picture to the front. You can make out the 2′ diameter tube for the concrete pier sticking out of the ground.
You need power to run things and extension cord’s just don’t cut it. Here is the trench that ran the conduits for power and a separate one for internet.
Finishing up the concrete pier. Initially we embedded stainless steel bolts into the concrete. When the building design changed to a dome design the pier design changed completely and these bolts were actually cut off as they were not needed.
Foundation is done. Next the walls. This view is looking just about exactly due north.
The walls are up but the roof is not complete. It was at this stage that we stopped construction as the rollers for the roll of roof were not designed. We had not yet decided to go with a full dome design. Winter was setting in so we covered the building with a tarp to protect it from the elements.
Note the tarp covering the building. This shot was probably taken in the early spring. We had decided to go with a full dome design. This necessitated expanding the size of the pier foundation by a factor of two bringing the size to 5’x5’x3′. This increased the overall weight of the pier foundation 2x to around 12,000lbs. The work to increase the size of the pier foundation required my contractor to basically cut up the floor and dig out around the existing pier to add the additional concrete. I felt bad for these guys as they did this around March when it was very cold outside.
You can see that they needed a jackhammer to dig into the ground to make way for the expansion of the pier. This addition was quite necessary as the new pier would be 10′ high and could support up to 500lbs. A 12,000 lb base makes for a ratio of about 24:1 worse case if we had 500lbs on top. Currently we have around 300lbs for a 40:1 ratio.
With the building complete all that was necessary was to finish the pier and wait for the dome to arrive. Here is my truck and trailer loaded with the pier and the dome getting ready to head north to complete the construction.
The pier weighs in at just over 1000lbs. This is not something you try to move with 4 of your buddies and a case of beer. We hired a local crane to come in an hoist the pier over the walls and into place on the new concrete base.
Once down the next task was to bolt the pier down. There are 12 – 8″ x 1/2″ lag bolts that were used to bolt the base to the concrete and another 8 at the 2′ level up that bolted the tension plate to the raised internal concrete pier. This made for a total of 20 5/8″ x 6″ holes that needed to be drilled into the concrete. Luckily, Matt has a Hilti power screw hammer drill for just such a task. Helps to have the right tool for the job.
I timed it. He could literally drill a 6″ x 5/8″ hole in about 15 seconds. Needless to say this drill laughs at concrete. The bolts we used were of the expansion type that are driven into the hole with a tool. In addition to the compression anchor we put in concrete resin epoxy into each hole. By drilling the holes in place and using the epoxy/compression anchor we were able to locate all 20 holes perfectly. You could never do this by placing the bolts ahead of time into the concrete. When final polar alignment was done we found that the entire setup was within 1 degree of true north. As the pier was lowered by the crane we had a few pencil marks on the wood floor to help us guide things in but I figured we’d probably be only able to place the pier around +/- 5 degrees at best. I was floored when the mount was put in place and we did our initial alignment. Every now and then Murphy closes his eyes.
The next task was to put on the dome. The dome comes with 4 fiberglass skirts that basically takes the square sides of the building and makes a very large flange to conform a round 10′ base for the dome to attach to the building. The dome manufacturer specifies that the external dimensions of the building needed to be 10′ 7.5″ with a chamfer edge all of the way around. My contractor made the exterior dimension of the square header to this exact dimension +/- 1/8″. Imagine my surprise then when I placed the skirts around the building and this is how they lined up.
I’d waited close to 9 months to get delivery on this and needed to move forward so my son came to my rescue once again. We made some stainless steel flashings that went over the top of the seam and covered things up. These worked fine and allows us to complete the construction on time. The only thing I can summarize here is that I know for a fact that my fiberglass dome was manufactured in the dead of winter back in Maryland. I’m guessing this was done in an unheated shop and the molds were very cold and thus shrunk in size. This resulted in the final pieces being way out of size and thus in need of adjustment.
To properly build the dome, the manufacturer recommends that you pre-build the dome on the ground in order to drill all of the holes that are required to fasten everything together. This is absolutely necessary as it would be quite impossible to do this in place without a whole lot of scaffolding to hold things together. In addition, by pre-assembling inside you are not fighting the wind and the elements while you are trying to make precise fitting. I chose to pre-build the dome in the conference room of my son’s shop. Once again he saves the day.
On the pre-assembly I stuck mostly to the instructions. One deviation is I doubled the number of holes and bolts that go up the sides of the dome quarter panels. The dome itself comes in 4 pieces. These are bolted together in two halves. A common problem many people have with this particular dome is that over time the two halves sag in at the top narrowing the space of the shutter. This causes the shutter to then malfunction. To help give better support I doubled the number of bolts on the flanges that join the two halves. Also, on all of the joining flat surfaces I used self adhesive foam gasket material to help seal the joints. This proved to be quite crucial, however I still had some leaks to contend with after final construction was completed.
You can see all of the dome quarter panels are up. The shutter is temporarily being supported open by two wooden rods, one of which is visible at the top of the dome. The shutter has not yet been put in place.
Once the quarter panels were up in place we put the final pieces together and it was done. I needed to do quite a bit of calking on all of the seams. We still had a few leaks so I went back and got exterior flexible flashing which is basically tar based tape. I put this around all of the exterior seams both on the building and on the dome. I waited a day and then painted everything. That appears to have done the trick and now everything is nice and dry, even after some horrendous thunderstorms.
Here is the final building. Dome in place. Lightening protection secured. All of the internal wiring is complete and we are now ready to look at the heavens.