A pre-cutter assembly includes at least one knife rotatable about a knife rotation axis between a retracted position and a deployed position, and an associated engagement arm rotatable about an arm rotation axis between a latch position securing the knife in the deployed position, and a release position allowing the knife to move into the retracted position. A magnet may be positioned for engagement with the engagement arm when the engagement arm is disposed in the latch position. The magnet is operable to apply a magnetic force to the engagement arm when engaged with the engagement arm to hold the engagement arm in the latch position thereby securing the knife in the deployed position. A cam shaft having a cam lobe may be rotated to selectively move the engagement arm between the release position and the latch position.