← Back: Sewing Machine Anatomy
A neat seam doesn’t just depend on the fabric or thread.
It depends on the settings.
Three parameters directly influence the result:
- stitch length
- tension
- stitch type (straight, zigzag…)
Stitch Length
The stitch length is the distance between two consecutive needle penetrations.
It is measured in millimeters (mm).
Stitch Too Short
- The fabric is perforated too frequently.
- The seam becomes rigid.
- The fabric may pucker.
- It is difficult to unpick.
On thin fabric, it can even weaken the fibers.
Stitch Too Long
- Basting-like appearance.
- Less strong.
- Can be useful temporarily.
A permanent seam that is too long lacks strength.
Reference Lengths
For classic fabric (cotton, poplin):
- 2.5 mm → standard
- 3 mm → visible seam
- 3.5 mm → more aesthetic topstitching
- 5 mm → basting stitch
These values are guidelines, not absolute rules.
Above all, don’t hesitate to test before you start.
The length depends on:
- fabric thickness
- fiber density
- seam function (assembly, topstitching, basting)
For thick fabric, slightly increase the length.
For very thin fabric, you can reduce it.
Tension
Tension adjusts the force applied to the upper thread.
A balanced stitch means the knot forms in the middle of the fabric’s thickness.
Why adjust tension?
Tension is adjusted when:
- loops appear underneath,
- loops appear on top,
- the stitch is uneven,
- the thread breaks.
Simple Principle
- Loops underneath → upper tension too loose.
- Loops on top → upper tension too tight.
Adjust gradually.
Always test on a scrap piece.
“Ideal” Values
There is no universal value.
The middle position (often around 4) is a starting point.
The setting depends on:
- the fabric,
- the thread,
- the needle.
The Zigzag Stitch
Two parameters:
- width (lateral spread)
- length (distance between stitches)
What is the zigzag stitch used for?
- Maintaining elasticity.
- Finishing an edge.
- Attaching elastic.
- Reinforcing a seam.
Common setting for finishing edges
- Width: 3-5 mm
- Length: 1.5-2.5 mm
Common setting for attaching elastic
- Width adapted to the elastic’s width.
- Medium length (2–3 mm).
Also…
The choice of stitch influences:
- strength,
- flexibility,
- aesthetics.
A straight stitch is strong but not stretchable.
A zigzag provides flexibility.
For jersey, a zigzag or a stretch stitch is often essential.
Key Takeaways
Before blaming the fabric or the machine:
- Check the stitch length.
- Check the tension.
- Test on a scrap piece.
Good settings prevent 80% of problems.
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The Needle Plate and Markings
