A semi-automatic split needle bar sewing machine (10) includes a sewing machine (12) which is driven by a motor (26) that drives a left needle (22) and a right neddle (23). A presser foot (24) is operated by presser lift actuator (30). The needles (22) and (23) can activate in unison or independently by use of fall out actuators (41) and (43), respectively. A control chassis (50) includes a microprocessor controller (51) that is programmable through an input panel (44). An edge detector (40) detects the edge of the material to provide feedback for the microprocessor controller(51). The microprocessor controller (51) is operable to sew a decorative pattern with mitered corners by sensing the pivot point of the mitered corner and automatically disangaging one of the needles (22) or (23). The microprocessor controller (51) then continues single needle sewing around the apex of the mitered corner by counting a predetermined number of stitches and varying the length of the stitches such that the needle is in the correct position when the single needle sewing again arrives at the pivot point on the other side of the mitered corner. In this manner, it is not necessary for the operator to manually adjust the length of the stitches around the apex of the mitered corner.