Two workmen were on a scissor-lift work platform elevated approximately 20 feet above grade. They were using a portable, electric, magnetic base drill to drill a hole in the bottom flange of a bridge's steel beam. As the hole was being drilled, the rotating drill bit suddenly jammed in the hole, the base broke loose from its magnet's hold on the underside of the steel beam, and the entire drill body rotated uncontrollably about the stuck drill bit. The uncontrolled, rotating drill body flailed its power cord wildly about. The flailing cord repeatedly struck and injured one of the workmen trapped on the elevated work platform.
Neal A. Growney & Assoc., LLC, was asked to investigate this accident and address the dangerous hazards of a magnetic drill rotating uncontrollably about its jammed drill bit. In order to demonstrate such dangerous and hazardous motion, NAGALLC improvised a test rig setup that provided the capability for simulating an operator's feeding, and the jamming of, a drill bit up in the underside of a steel beam. The test rig essentially consisted of a horizontal steel beam with an automotive clutch affixed to it. The magnetic base drill was mounted on the rig in an upside down position. The clutch's pressure plate was fixed to the steel beam. The clutch disc was mounted on a cut-down automotive transmission's front input shaft, whose pilot end was mounted in the drill's chuck. The drill and the clutch were arranged to be operated independently and remotely, each with a long lever so as to eliminate exposing an operator to any dangerous hazard when the drill jammed. The clutch and the drill's feed lever could both be operated independently to load and unload the drill as well as to simulate an operator's drilling a hole upward into the bottom of a steel beam. The clutch could also be applied to stop the drill bit's rotation, thereby simulating the jamming of the drill bit in the steel beam.