A cutting mechanism for a dunnage conversion machine that selectively cuts dunnage sheet stock drawable through the cutting mechanism, the cutting mechanism comprising: a frame supporting opposed blades for cutting the sheet stock; the opposed blades including a driven blade having a driven cutting edge and a secondary blade having a secondary cutting edge each supported relative to the frame and defining a path therebetween along which the sheet stock to be cut may be passed, the driven blade being supported relative to the frame for linear translation towards the secondary blade to cut the sheet stock; a blade guard coupled between the frame and the driven blade, the blade guard configured to be commonly movable with the driven blade between an engaged position of the blade guard where the blade guard is commonly movable with the driven blade and a disengaged position of the blade guard where the driven blade translates independently of the blade guard; and a slot and key arrangement (140, 150) for guiding movement of the blade guard and the driven blade relative to one another, one of the blade guard and the driven blade including the key (144, 154) of the arrangement, and the other of the blade guard and the driven blade including the slot (142, 152) of the arrangement, where the slot is shaped to maintain common movement of the blade guard and the driven blade until the blade guard is in the disengaged position, and thereafter to allow movement of the driven blade independent from the blade guard; such that the blade guard restricts cutting of the sheet stock and restricts independent movement of the driven blade separate from the blade guard until the blade guard is moved to the disengaged position, the blade guard projecting beyond the driven cutting edge of the driven blade and restricting movement of the driven cutting edge beyond an outer periphery of the blade guard until the driven cutting edge is within a predetermined distance from the secondary cutting edge of the secondary blade. a frame supporting opposed blades for cutting the sheet stock; the opposed blades including a driven blade having a driven cutting edge and a secondary blade having a secondary cutting edge each supported relative to the frame and defining a path therebetween along which the sheet stock to be cut may be passed, the driven blade being supported relative to the frame for linear translation towards the secondary blade to cut the sheet stock; a blade guard coupled between the frame and the driven blade, the blade guard configured to be commonly movable with the driven blade between an engaged position of the blade guard where the blade guard is commonly movable with the driven blade and a disengaged position of the blade guard where the driven blade translates independently of the blade guard; and a slot and key arrangement (140, 150) for guiding movement of the blade guard and the driven blade relative to one another, one of the blade guard and the driven blade including the key (144, 154) of the arrangement, and the other of the blade guard and the driven blade including the slot (142, 152) of the arrangement, where the slot is shaped to maintain common movement of the blade guard and the driven blade until the blade guard is in the disengaged position, and thereafter to allow movement of the driven blade independent from the blade guard; such that the blade guard restricts cutting of the sheet stock and restricts independent movement of the driven blade separate from the blade guard until the blade guard is moved to the disengaged position, the blade guard projecting beyond the driven cutting edge of the driven blade and restricting movement of the driven cutting edge beyond an outer periphery of the blade guard until the driven cutting edge is within a predetermined distance from the secondary cutting edge of the secondary blade.