EMPLOYEE WAS CHANGING A TRIPLE ROLL MAGNET BEARING. ROLLER WAS LIFTED OUT OF PLACE & PARTIALLY BLOCKED TO FACILITATE WORK. ROLLER SHIFTED CATCHING EE'S RT. RING FINGER BETWEEN THE ROLLER & MACHINE FRAME. EE SUFFERED 1/2""LACERATION TO RT. RING FINGERTIP RESULTING IN 4 STITCHES. EE WAS WEARING GLOVES.