A circular cutting unit operable to partially cut a cable along a cutting plane that is perpendicular to a cable axis comprising: a drive disc rotatable about the cable axis; a pair of knife holders mounted to the drive disc, each of the knife holders configured to receive and retain a knife blade; an adjustment disc rotatable about the cable axis, the adjustment disc including a pair of adjusting elements that each engage one of the knife holders, wherein a relative change in an angle of the adjustment disc relative to the drive disc causes movement of the knife blades in the cutting plane toward or away from each other; and a primary drive assembly operable to rotate the drive disc and the adjustment disc at a cutting speed; an adjustment drive assembly coupled to the adjustment disc, wherein operation of the adjustment drive assembly modifies a rotation speed of the adjustment disc relative to the rotational cutting speed of the drive disc for an adjustment period to create a change in an angle of the adjustment disc relative to the drive disc to cause movement of the knife blades in the cutting plane toward or away from each other; wherein the primary drive assembly includes a drive pulley connected to the drive disc by a first pulley belt and an adjustment pulley connected to the adjustment disc by a second pulley belt, wherein the drive pulley and the adjustment pulley are rotationally coupled to a primary drive shaft rotated at a cutting speed by a primary drive motor, wherein the adjustment drive assembly is coupled to the adjustment pulley, wherein the adjustment drive assembly is operable to modify the rotational speed of the adjustment pulley, characterized in that the primary drive shaft includes a spiral groove, and the adjustment drive assembly includes a ball nut movable along the spiral groove. a drive disc rotatable about the cable axis; a pair of knife holders mounted to the drive disc, each of the knife holders configured to receive and retain a knife blade; an adjustment disc rotatable about the cable axis, the adjustment disc including a pair of adjusting elements that each engage one of the knife holders, wherein a relative change in an angle of the adjustment disc relative to the drive disc causes movement of the knife blades in the cutting plane toward or away from each other; and a primary drive assembly operable to rotate the drive disc and the adjustment disc at a cutting speed; an adjustment drive assembly coupled to the adjustment disc, wherein operation of the adjustment drive assembly modifies a rotation speed of the adjustment disc relative to the rotational cutting speed of the drive disc for an adjustment period to create a change in an angle of the adjustment disc relative to the drive disc to cause movement of the knife blades in the cutting plane toward or away from each other; wherein the primary drive assembly includes a drive pulley connected to the drive disc by a first pulley belt and an adjustment pulley connected to the adjustment disc by a second pulley belt, wherein the drive pulley and the adjustment pulley are rotationally coupled to a primary drive shaft rotated at a cutting speed by a primary drive motor, wherein the adjustment drive assembly is coupled to the adjustment pulley, wherein the adjustment drive assembly is operable to modify the rotational speed of the adjustment pulley, characterized in that the primary drive shaft includes a spiral groove, and the adjustment drive assembly includes a ball nut movable along the spiral groove.