We're getting very close to getting Bertha in her new home and ready for action. Thanks to the generous help AGAIN from my friend Matt Green, the first section of the pier has been cut and welded into place. The design of the pier is a bit unusual in that it is very tall and cannot be anchored into the ground. The observatory floor is actually what would be the fourth floor of the house, and given that the walls are 12' tall, we had to build another level up from the third floor to be able to see out of the dome. Given that the scope is then 11' or so off the floor, a multi-segment pier was needed. The drawing below illustrates how the sections are tied together:
The pier is divided into three pieces. The top two pieces are from Pier-Tech. This is the Pier-Tech 2 / Pier-Tech 1 Telescope Pier Combo. The top section telescopes 20", while maintaining polar alignment. The section section is the Pier Tech 1 component, which is stationary. The maximum length of the Pier Tech 1 is 48", so we were 5'-6" short. Various material choices were considered, but I decided on 1/4" steel from Nivert Metal Supply. I ordered the steel on a Monday afternoon and they delivered it cut and ready to go on Thursday, with a 40' truck. The bottom portion of the pier is 8" x 8" x 1/4" steel tubing. To distribute the weight across the observatory floor, a 4' x 4' x 1/4" steel plate was welded to the bottom of the pier. I then drilled holes every 12" - 16" to secure the plate to the floor.
Pier-Tech 2 Telescopic Pier
Pier-Tech 1 Sub Pier
This is how the pieces will look all together:
To construct the steel portion of the pier, we first had to cut off about 4" as I had not accounted for a gap of 2" between each section of the pier. My assumption was that the pieces would be bolted together, but the actual design suggests a 2" gap to allow for leveling and adjustments. Fortunately cutting through steel is not a problem for Matt, who brought his grinder and expertise.
Matt Shortening the Pier
We carried the 130lb steel tube down from the attic and outside to the driveway. We setup a portable work bench and Matt made it look easy. He cut through all four sides of the tube and then ground the edges smooth with a slight bevel to help hold the weld. We then carried the steel back up stairs and after catching our breath and hoping we wouldn't need to call 911, decided that was all we needed to do for one day.
On Thursday, Matt came back with his welding gear, and we began the adventure of welding the pier to the steel plate.
Matt Ready to Weld
Matt was able to borrow a friend's portable MIG welder that simply plugs into a 110 outlet. Knowing that the process would kick off a bunch of smoke, I closed the door to the observatory and opened up the shutter on the dome. This gave us a great chimney effect and pulled the smoke right out of the room.
Matt Welding the Pier
We had three problems to solve before we could weld the pier. First, all of the components from Pier-Tech are aluminum, and while there are some ways to weld steel to aluminum, those were not options for us. We solved this problem by getting a 12" x 12" x 1/4" steel plate to weld to the top of the steel tube and then we would sandwich it with bolts to the aluminum plate of the Pier-Tech 1. Matt was able to drill the holes using a magnetic drill to make the holes for the bolts. He also had the forethought to make a hole in the center of the plate so I could add sand later if needed.
Second, we had to align the pier to North, or actually on the North Celestial Pole. To do this, I taped a laser level to my camera tripod and locked in all movement of the tripod except for vertical adjustment. I then aimed the laser at Polaris, and then tilted the tripod down through the hole in the observatory floor above the pier, marking the line on the lower floor where the steel plate is located. I then double-checked the alignment by placing a compass that was adjusted for the 12 degree offset between North and the Celestial North Pole. The laser line was right over the mark on the compass, so I knew I was certainly close enough to make any other adjustments with the wedge once the scope was mounted.
The third problem was to make sure the pier was plumb, as any tilt would be exaggerated over the 12' length.
The Finished Product
Using a 4' level, I held it against two sides while Matt tacked down the pier. Of course I screwed that part up, so Matt had to cut one of the welds and do it again. Fortunately he found enough patience to tolerate my goof and didn't weld my feet to the floor. We then lifted the steel tube and the plate onto a couple 2" x 4"s to keep the heat from the welding process off the floor. Matt expertly welded the pier to the plate and now it's ready to go.
I did a few tests of pier stability by placing a glass measuring cup half-filled with water on the top plate of the pier. I walked around on the ground floor of the observatory, and also on the steel plate. I saw a good deal of movement in the water, so I decided to go ahead and add the sand to the inside of the steel pier. I added about 3.5 bags of sand, and it is much more stable. The vibrations seem to settle down almost instantly now, which should prove very helpful when the rest of the pier and the scope are mounted.