1. Regulating the thread tension: For perfect stitching the tension of the upper and lower threads should be equal. The needle and bobbin threads will be locked at the centre of the thickness of the fabric.
Imperfect stitching occurs when one tension ( needle or bobbin) is stronger than the other as follows:
- when the upper tension is too tight, loops appear on the upper surface of the work.
- when the lower tension is too tight, loops appear in the lower surface is the work.
- when both threads are too loose, floating stitches are the result.
- when upper and lower threads are too tight, the fabric will become wrinkled. The thread will then break easily.
To regulate the tension
- when the upper thread is too tight, loosen the tension disc.
- when the upper thread is too loose, tighten the tension disc.
- when the under thread is too tight, lift out the bobbin case and loosen the screw if the tension spring leaf outside the bobbin case with screw driver.
2. Skipped stitches: This may be caused by:
- a bent or blunt needle.
- a needle of incorrect length.
- an improperly set needle.
- a needle not suitable to size of thread.
3. Puckers in fabric: This may be caused by:
- a blunt needle.
- a very right tension.
4. Breaking of machine needle: This may be caused by:
- improper setting of needle.
- pulling fabric without raising needle.
- sewing over a pin on fabric.
- sewing over many layers of fabric.
5. Constant breaking of thread: This may be caused by:
- bobbin thread different from the upper thread.
- tension of the thread too tight.
- use of poor quality thread.
- incorrect threading of machine.
- uneven winding of the bobbin.
- bobbin thread too full.