Employees were reinstalling the frame of a mechanical guard onto a raw sugar mixer. A chain fall was used to position the frame so it's weight was resting on the lower pedestal. The chain block was then unhooked, and an employee used a hammer to position the frame so the top bolt holes would be aligned. The bottom of the frame slipped off the pedestal and the frame fell two feet down onto the employee's right arm causing fractures to the radius and ulna.