Abstract: A first stop member (74) is connected to and extends upwardly, perpendicular to a longitudinal frame member (72). A second stop member (80) is connected to and projects upwardly and perpendicular to a base member (82). The base member (82) is supported by and is guided along the frame member (72) by a longitudinal rib (84) on the frame member (72) and a longitudinal recess (86) formed in the bottom of the base member (82). The stop members (74, 80) include shaft receiving openings (78, 120). A forward portion of a rotary shaft (12) projects forwardly through the opening (78) in the forward stop member (74) and then projects forwardly through a guide passageway in a guide member (52) having a forward end surface (53). A rear portion of the shaft (12) projects through opening (120) in the rear stop member (80). The shaft (12) includes an abutment (46) that is positioned between the two stop members (74, 80). The cutting tip member (14) is pivotally connected to the forward end of the shaft (12).