An employee was readjusting a sensor that controls tool pick up and tool changes. While he tried to check the position of the sensor, a coworker operated the Onsrud machine. The hood and airlines were not reattached. The back bush would not operate without the airline, so the injured employee attempted to hold up the back brush with his hand. The machine's platen dropped to pick up a tool; when it ascended, it caught the employee's thumb between the two platens, severely lacerating and fracturing it.