Cycle type describes the way in which succeeding tool moves are performed when cutting a groove. Two Cycle Types use the center of the groove. The center is defined to be either the lowest point in the groove or, if the lowest point lies on a horizontal line, the center of that line.
Center Sequential
The first move is down the center of the groove. The next moves are toward one edge of the groove (to the left for OD groove). When the first half of the groove is cut, the tool returns to the center and moves toward the other edge (to the right for OD groove).
Center Alternate
The first move is down the center of the groove. The next move is to one side of the center (to the left side for OD groove), followed by a move on the other side. The cutting moves alternate—from one side of the center to the other—until the groove is complete.
Sequential
The first move is down one edge of the groove (the right edge for OD groove). The next moves are in the direction of the other edge (to the left for OD groove).