An employee and a coworker were operating a saw with dual palm buttons. The employee was on the left side holding a 2 x 4 wooden board to be cut toward the back stop on the machine. The coworker was on the right side and actuated the palm buttons while the employee's left thumb was in the point of operation. When the blade came up, it amputated approximately 1/4" of the employee's left thumb tip. The saw was unguarded at the time.