Abstract: At 8:05 a.m. on December 4, 2021, an employee was working as a tool maker at a large aerospace parts manufacturing plant machine shop area. A coworker in the maintenance department asked the employee to design and create an aluminum bracket for a roller machine which would hold the bearings. The employee was using a Sharp Model VH3 Vertical & Horizontal Milling Machine to bore a hole in the aluminum. Before attempting to drill the hole, the employee was attaching the 11-inch by 8-inch by 1-inch piece of aluminum to a clamp. The employee had his hand on the clamp, approximately 9 inches from the bit. When the bit broke through the stock, the metal slipped from the clamp and slid up the bit striking the employee's left arm. The employee had failed to tighten the holding clamp sufficiently and failed to correctly adjust the speed selector, which was set high at 1,350 revolultions per mimute (RPM). The speed should have been set no higher than 1,100 RPM for that bit and material. The employee fractured his left arm and was treated by local Fire Department Paramedics onsite. The employee was transported to a medical center by a coworker (Supervisor), where he was admitted for further treatment.