During operation, first observe the stitch formation:
· If the upper thread floats on the fabric surface and forms loops, turn the upper thread tension knob clockwise to increase pressure.
· If the lower thread appears as a straight line exposed on the surface, adjust the lower thread tension by fine-tuning the bobbin case screw.
For elastic fabrics, it is recommended to increase the differential feed ratio by 10%–15% to compensate for stretch deformation.
During adjustment, follow the principle of “micro adjustment and step-by-step testing.” Each rotation of the tension knob should be controlled within 15°, and a 5 cm test seam should be sewn on scrap material from the same batch to verify the result.
It is also important to note that for every 1 mm increase in fabric thickness, the upper thread tension should be increased by approximately 0.3–0.5 N. A tension tester can be used to calibrate the values and record them in an equipment parameter reference chart for future consistency.