A knife carriage for face-to-face weaving machines has a supporting surface with interchangeable, adjustable sliding parts which direct the knife carriage in relation to a guiding section. A cutting instrument separates top and bottom fabrics from each other. The instrument has attachment(s) for a drive cord from a drive mechanism for the knife carriage. The sliding parts and the attachment(s) for the drive cord on the supporting surface have a device, which when tightened, makes the attachment line of the device coincide respectively with the contact line of the sliding parts with the supporting surface, and surface the contact surface of the attachment(s) with the supporting surface. The length of the supporting surface is smaller than the distance between the extremities of the sliding parts protruding in relation to the supporting surface in longitudinal direction of the knife carriage. The width of the supporting surface is smaller than the distance between the sides of the sliding parts protruding in relation to the supporting surface in transverse direction of the knife carriage.