Hull, who worked on the project with Mark Kutney, an architectural conservator for Facilities Management, said historical astronomy expert Fred Orthlieb, the retired Isaiah V. Williamson Professor of Civil and Mechanical Engineering at Swarthmore College, studied the dome and the rollers and made a recommendation.
“He told us the rollers, which were pretty much original to 1884, were going bad,” Hull said. “They have these little cylinder ball bearings inside of them and over time they were getting bent out of round. Basically, the only way to fix it was to replace those rollers.”
Jimmy Davidson, the observatory’s instrument and laboratory technologist, led the project. He and Hull worked with Peter Dow, a machinist for the astronomy department who builds instruments from plans drawn up by the faculty and graduate students and maintains and repairs mechanical problems with the department’s telescopes. Dow and Davidson took training to operate a hydraulic lift, as well as harness and safety training, to work on the outside of the dome.
“The original rollers were basically just large roller bearings, but the rollers inside were worn down to the point that they were twisting and jamming,” Dow said. “Our goal was to keep as much of the original design as possible, while also bringing the moving components up to modern standards and making it easier to work on in the future.
“The rollers themselves, originally an odd 3 1/16 inches in diameter, were replaced with standard 2½-inch yoke rollers with modern bearings so that any subsequent replacements should be easy to source,” Dow said.
The original custom-built rollers were designed to fit very precisely in their steel track.
“They were made to such a close fit with the tracks that when the tracks were painted, the paint thickness was enough to cause the rollers to rub against the top painted surface of the track,” Dow said.
The Department of Astronomy kept the existing tracks but modified them with a stainless-steel track on which the bearings roll.