Abstract: Blade support unit, for receiving a replaceable blade, includes a blade receiving slot defined by a rigid base member and a second flexible member, the members having blade engaging surfaces and being maintained with fixed separation equal to the blade thickness along a first edge of the slot. A clamping member passes through extensions of the members beyond the slot boundaries, and an elongated tightening lever engages the clamping member so that force applied to the lever is transferred through the clamping member to clamp the blade between the two members.