A client asked me to inspect 2 more Fries 15-perf pull-across 3×65 IMAX-format movements. At first, this looked like it would be a simple project as I rebuilt a similar movement to these recently. However, no simple repair is ever as simple as it seems, and during my initial examination of the first of these movements, I noticed that the flywheel was wobbling when I spun it by hand.
The gears that time the pull-down claw and registration pins were not wobbling, so I thought I could just make an intermediate spacer that threaded onto the drive shaft, which would give me a flat surface to dowel pin and screw the flywheel to the pull-down drive gear. I made this precision lapped spacer, thinking that the two flat surfaces would hold everything flat to the gear, threaded it onto the pull-down drive shaft, mounted the flywheel to test my theory, and wouldn’t you know it, everything still wobbled.
After a little bit of head scratching and analysis, I discovered that the threaded section that holds the flywheel in place is an insert that is dowel pinned onto the pull-down drive shaft. This threaded section is not square to the main drive shaft, and that is what was causing the wobble.
After going through 4 or 5 different versions of spacers, I finally had to abandon using the threaded portion of the shaft as the pilot for the flywheel, and instead made two new spacers, polished to be flat on both faces. One spacer was simply a retaining ring to hold the pull-down gear on its bearing assembly. The other spacer fits over that retaining ring so that one of the flat surfaces fits flush against the main pull-down gear, and the other flat surface fits flush against the back of the flywheel.
Four screws were added to the assembly so that they went through the flywheel, through the hollow spacer, and threaded into the pull-down gear. That seems to have now taken the wobble out of the flywheel. The flywheel acts as the coupling between the camera body and the movement, so everything had to be figured out backwards from the original keyway positions. Everything still has to come apart to be balanced before final reassembly.
