Rutherfurd Observatory: Repairing an Iconic Dome
In 2017, Columbia University’s Dr. Jana Grcevich, then Outreach Coordinator for Columbia’s Astronomy & Astrophysics Department invited me to examine the venerable but aging copper clad wooden dome atop historic Pupin Hall. [1] At that time the dome was already 90 years old and getting cantankerous. Dr. Grcevich explained that the dome was prone to “sticking” in four locations. Sticking meant that it would not rotate past these spots without some additional human muscle power … three or four husky students would grab the dome and with ‘the old college try’, would push it past those spots. To facilitate this, there were indicators of blue painter’s tape near those spots, with labeling indicating “Gun it”, i.e. to increase the speed of the two-speed motor to gain more momentum to overcome those sticky spots. This was not a good situation, and it was indicative of many decades of neglect of the relatively simple mechanism. By 2019, the situation was becoming untenable, and I was invited to come and examine the dome to make a proposal for repairs.
For this trip, I enlisted a colleague, Dr. Frederick Orthlieb, retired Emeritus Professor of Mechanical Engineering at Swarthmore College, who has extensive experience repairing these old domes.
The dome was installed when Pupin Hall was built in 1927, making it the same age as Amateur Astronomers Association, Inc., and it will celebrate its 100th anniversary when we celebrate ours. It was designed by the firm of Towner and Sellew Associates, chiefly by partner and engineer Roland W. Sellew. Sellew also designed the mount and column for the 31.4 cm refractor to go in it, which Columbia purchased from the Alvan Clark & Sons Corporation, with a lens by C. A. Robert Lundin. [2]
The issues we uncovered were typical of Sellew-designed domes and fortunately none were fatal flaws. The design of the dome incorporates 4-inch railroad rails formed into a 28-foot diameter circle that the dome rolls on. There are 16 large roller wheels made of cast iron and predictably they were worn by as much as ½-inch of their diameter after nearly a century of operation. This in turn lowered the entire dome until it was dragging on the outside of the masonry support cylinder. A further complication was that a series of eight hold-down brackets, meant to keep the dome from lifting off in a storm, were seized from corrosion and lack of maintenance, so that they would catch on misalignments of the rail joints. This combination of factors caused Columbia to overtighten the tension on the cable that rotates the dome. It lays in an angle-iron ‘tray’ around the circumference of the dome’s interior, attached to its support structure. This overtightening deformed the cable tray, which ironically had the reverse effect of lowering the cable’s “purchase” or grab of the tray. Compounding all was the lack of lubrication throughout the dome’s moving parts … wheels; pulley sheaves; gears and the drive mechanism.
Other issues included a worn drive cable ready to snap and the safety hazard of the drive mechanism being dangerously exposed to the astronomers, public outreach visitors and students.
A proposal was then made to repair the dome to operable condition and to inspect and lubricate the dome’s shutter, too. However, the money was not available at the time and the project languished. Then Covid-19 hit, and the campus shut down until 2022. When the campus opened, the department endeavored to use its observatory, but it all came to a head when, in the late Spring of that year, the motor gave out and the dome was completely inoperable. Columbia attempted to disengage the drive from the motor so the dome could be moved, with a lot of difficulty, by hand power. But clearly something had to be done and the University requested a new quote. A contract was let out and work began for the repairs, now to include a completely new drive motor and gearing, with a safety cover, and a new cable and cable tray. Work commenced March 20, 2023 and was completed by the end of May.
Work done included removing the steel skirt in front of the roller wheels, and then grinding the roller face of each wheel flat. This was done in situ. The wheels were lubricated and then the dome was painstakingly raised up in two flights of ¼”, using 64 ¼ inch steel shims x (2), so that the dome was raised fully ½ inch. The hold down brackets were lubricated so they could swing freely and not jam at the rail joints. The joints themselves were realigned to remove edges that could catch the hold down ‘fingers’ and at that point, the dome could roll freely. A new cable tray was fabricated and installed with stronger joints and a new motor and gearbox were designed and installed along with a brand-new cable.
Columbia’s own electrical shop provided a new hookup including a safety cutoff switch next to the control box for the motor. Power is via 208 V for the motor and 110 V for the hand paddle switch which was moved over to the telescope pier for easier access during use. At the end of May, the motor was powered up and tested and the dome rolled beautifully and quietly. Gone were the creaks, groans and bangs associated with the old, decrepit system. Additionally, all the interior red lights were repaired, and 110-volt wall receptacles were installed for powering the computers and peripherals.
This fall, Columbia will continue its free in-person lecture series, and traditionally they have had public viewing in the Rutherfurd Observatory dome after the lectures. Now that the dome is fully functional again, perhaps we can look forward to reinstitution of that wonderful experience!
